MicroencapsulationSecond EditionDK3090_half-series-title.qxd 9/9/05 10:25 AM Page ADRUGS AND THE PHARMACEUTICAL SCIENCESExecutive EditorJames SwarbrickPharmaceuTech, Inc.Pinehurst, North CarolinaAdvisory BoardLarry L. AugsburgerUniversity of MarylandBaltimore, MarylandJennifer B. DressmanJohann Wolfgang Goethe UniversityFrankfurt, GermanyJeffrey A. HughesUniversity of Florida College of PharmacyGainesville, FloridaTrevor M. JonesThe Association of theBritish Pharmaceutical IndustryLondon, United KingdomVincent H. L. LeeUniversity of Southern CaliforniaLos Angeles, CaliforniaJerome P. SkellyAlexandria, VirginiaGeoffrey T. TuckerUniversity of SheffieldRoyal Hallamshire HospitalSheffield, United KingdomHarry G. BrittainCenter for Pharmaceutical PhysicsMilford, New JerseyAnthony J. HickeyUniversity of North Carolina School of PharmacyChapel Hill, North CarolinaAjaz HussainU.S. Food and Drug AdministrationFrederick, MarylandHans E. JungingerLeiden/Amsterdam Centerfor Drug ResearchLeiden, The NetherlandsStephen G. SchulmanUniversity of FloridaGainesville, FloridaElizabeth M. ToppUniversity of Kansas School of PharmacyLawrence, KansasPeter YorkUniversity of Bradford School of PharmacyBradford, United KingdomDK3090_half-series-title.qxd 9/9/05 10:25 AM Page BDRUGS AND THE PHARMACEUTICAL SCIENCESA Series of Textbooks and Monographs1. Pharmacokinetics, Milo Gibaldi and Donald Perrier2. Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control,Sidney H. Willig, Murray M. Tuckerman, and William S. Hitchings IV3. Microencapsulation, edited by J. R. Nixon4. Drug Metabolism: Chemical and Biochemical Aspects, Bernard Testa and Peter Jenner5. New Drugs: Discovery and Development, edited by Alan A. Rubin6. Sustained and Controlled Release Drug Delivery Systems, edited by Joseph R. Robinson7. Modern Pharmaceutics, edited by Gilbert S. Banker and Christopher T. Rhodes8. Prescription Drugs in Short Supply: Case Histories, Michael A. Schwartz9. Activated Charcoal: Antidotal and Other Medical Uses, David O. Cooney10. Concepts in Drug Metabolism (in two parts), edited by Peter Jenner and Bernard Testa11. Pharmaceutical Analysis: Modern Methods (in two parts), edited by James W. Munson12. Techniques of Solubilization of Drugs, edited by Samuel H. Yalkowsky13. Orphan Drugs, edited by Fred E. Karch14. Novel Drug Delivery Systems: Fundamentals, Developmental Concepts, BiomedicalAssessments, Yie W. Chien15. Pharmacokinetics: Second Edition, Revised and Expanded, Milo Gibaldi and Donald Perrier16. Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Second Edition, Revised and Expanded, Sidney H. Willig, Murray M. Tuckerman, and William S. Hitchings IV17. Formulation of Veterinary Dosage Forms, edited by Jack Blodinger18. Dermatological Formulations: Percutaneous Absorption, Brian W. Barry19. The Clinical Research Process in the Pharmaceutical Industry, edited by Gary M. Matoren20. Microencapsulation and Related Drug Processes, Patrick B. Deasy21. Drugs and Nutrients: The Interactive Effects, edited by Daphne A. Roe and T. Colin Campbell22. Biotechnology of Industrial Antibiotics, Erick J. Vandamme23. Pharmaceutical Process Validation, edited by Bernard T. Loftus and Robert A. Nash24. Anticancer and Interferon Agents: Synthesis and Properties, edited by Raphael M. Ottenbrite and George B. Butler25. Pharmaceutical Statistics: Practical and Clinical Applications, Sanford Bolton26. Drug Dynamics for Analytical, Clinical, and Biological Chemists, Benjamin J. Gudzinowicz, Burrows T. Younkin, Jr., and Michael J. Gudzinowicz27. Modern Analysis of Antibiotics, edited by Adjoran Aszalos28. Solubility and Related Properties, Kenneth C. James29. Controlled Drug Delivery: Fundamentals and Applications, Second Edition, Revised and Expanded, edited by Joseph R. Robinson and Vincent H. Lee30. New Drug Approval Process: Clinical and Regulatory Management,edited by Richard A. Guarino31. Transdermal Controlled Systemic Medications, edited by Yie W. Chien32. Drug Delivery Devices: Fundamentals and Applications, edited by Praveen TyleDK3090_half-series-title.qxd 9/9/05 10:25 AM Page C33. Pharmacokinetics: Regulatory Industrial Academic Perspectives,edited by Peter G. Welling and Francis L. S. Tse34. Clinical Drug Trials and Tribulations, edited by Allen E. Cato35. Transdermal Drug Delivery: Developmental Issues and Research Initiatives,edited by Jonathan Hadgraft and Richard H. Guy36. Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms,edited by James W. McGinity37. Pharmaceutical Pelletization Technology, edited by Isaac Ghebre-Sellassie38. Good Laboratory Practice Regulations, edited by Allen F. Hirsch39. Nasal Systemic Drug Delivery, Yie W. Chien, Kenneth S. E. Su, and Shyi-Feu Chang40. Modern Pharmaceutics: Second Edition, Revised and Expanded,edited by Gilbert S. Banker and Christopher T. Rhodes41. Specialized Drug Delivery Systems: Manufacturing and Production Technology,edited by Praveen Tyle42. Topical Drug Delivery Formulations, edited by David W. Osborne and Anton H. Amann43. Drug Stability: Principles and Practices, Jens T. Carstensen44. Pharmaceutical Statistics: Practical and Clinical Applications, Second Edition, Revised and Expanded, Sanford Bolton45. Biodegradable Polymers as Drug Delivery Systems, edited by Mark Chasin and Robert Langer46. Preclinical Drug Disposition: A Laboratory Handbook, Francis L. S. Tse and James J. Jaffe47. HPLC in the Pharmaceutical Industry, edited by Godwin W. Fong and Stanley K. Lam48. Pharmaceutical Bioequivalence, edited by Peter G. Welling, Francis L. S. Tse, and Shrikant V. Dinghe49. Pharmaceutical Dissolution Testing, Umesh V. Banakar50. Novel Drug Delivery Systems: Second Edition, Revised and Expanded, Yie W. Chien51. Managing the Clinical Drug Development Process, David M. Cocchetto and Ronald V. Nardi52. Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Third Edition, edited by Sidney H. Willig and James R. Stoker53. Prodrugs: Topical and Ocular Drug Delivery, edited by Kenneth B. Sloan54. Pharmaceutical Inhalation Aerosol Technology, edited by Anthony J. Hickey55. Radiopharmaceuticals: Chemistry and Pharmacology, edited by Adrian D. Nunn56. New Drug Approval Process: Second Edition, Revised and Expanded, edited by Richard A. Guarino57. Pharmaceutical Process Validation: Second Edition, Revised and Expanded, edited by Ira R. Berry and Robert A. Nash58. Ophthalmic Drug Delivery Systems, edited by Ashim K. Mitra59. Pharmaceutical Skin Penetration Enhancement, edited by Kenneth A. Walters and Jonathan Hadgraft60. Colonic Drug Absorption and Metabolism, edited by Peter R. Bieck61. Pharmaceutical Particulate Carriers: Therapeutic Applications, edited by Alain Rolland62. Drug Permeation Enhancement: Theory and Applications, edited by Dean S. Hsieh63. Glycopeptide Antibiotics, edited by Ramakrishnan Nagarajan64. Achieving Sterility in Medical and Pharmaceutical Products, Nigel A. Halls65. Multiparticulate Oral Drug Delivery, edited by Isaac Ghebre-SellassieDK3090_half-series-title.qxd 9/9/05 10:25 AM Page D66. Colloidal Drug Delivery Systems, edited by Jrg Kreuter67. Pharmacokinetics: Regulatory Industrial Academic Perspectives, Second Edition, edited by Peter G. Welling and Francis L. S. Tse68. Drug Stability: Principles and Practices, Second Edition, Revised and Expanded, Jens T. Carstensen69. Good Laboratory Practice Regulations: Second Edition, Revised and Expanded, edited by Sandy Weinberg70. Physical Characterization of Pharmaceutical Solids, edited by Harry G. Brittain71. Pharmaceutical Powder Compaction Technology, edited by Gran Alderborn and Christer Nystrm72. Modern Pharmaceutics: Third Edition, Revised and Expanded, edited by Gilbert S. Bankerand Christopher T. Rhodes73. Microencapsulation: Methods and Industrial Applications, edited by Simon Benita74. Oral Mucosal Drug Delivery, edited by Michael J. Rathbone75. Clinical Research in Pharmaceutical Development, edited by Barry Bleidt and Michael Montagne76. The Drug Development Process: Increasing Efficiency and Cost Effectiveness, edited by Peter G. Welling, Louis Lasagna, and Umesh V. Banakar77. Microparticulate Systems for the Delivery of Proteins and Vaccines, edited by Smadar Cohen and Howard Bernstein78. Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control, Fourth Edition, Revised and Expanded, Sidney H. Willig and James R. Stoker79. Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms: Second Edition, Revised and Expanded, edited by James W. McGinity80. Pharmaceutical Statistics: Practical and Clinical Applications, Third Edition, Sanford Bolton81. Handbook of Pharmaceutical Granulation Technology, edited by Dilip M. Parikh82. Biotechnology of Antibiotics: Second Edition, Revised and Expanded, edited by William R. Strohl83. Mechanisms of Transdermal Drug Delivery, edited by Russell O. Potts and Richard H. Guy84. Pharmaceutical Enzymes, edited by Albert Lauwers and Simon Scharp85. Development of Biopharmaceutical Parenteral Dosage Forms, edited by John A. Bontempo86. Pharmaceutical Project Management, edited by Tony Kennedy87. Drug Products for Clinical Trials: An International Guide to Formulation Production Quality Control, edited by Donald C. Monkhouse and Christopher T. Rhodes88. Development and Formulation of Veterinary Dosage Forms: Second Edition, Revised and Expanded, edited by Gregory E. Hardee and J. Desmond Baggot89. Receptor-Based Drug Design, edited by Paul Leff90. Automation and Validation of Information in Pharmaceutical Processing, edited by Joseph F. deSpautz91. Dermal Absorption and Toxicity Assessment, edited by Michael S. Roberts and Kenneth A. Walters92. Pharmaceutical Experimental Design, Gareth A. Lewis, Didier Mathieu, and Roger Phan-Tan-Luu93. Preparing for FDA Pre-Approval Inspections, edited by Martin D. Hynes III94. Pharmaceutical Excipients: Characterization by IR, Raman, and NMR Spectroscopy, David E. Bugay and W. Paul FindlayDK3090_half-series-title.qxd 9/9/05 10:25 AM Page E95. Polymorphism in Pharmaceutical Solids, edited by Harry G. Brittain96. Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products, edited by Louis Rey and Joan C. May97. Percutaneous Absorption: DrugsCosmeticsMechanismsMethodology, Third Edition,Revised and Expanded, edited by Robert L. Bronaugh and Howard I. Maibach98. Bioadhesive Drug Delivery Systems: Fundamentals, Novel Approaches, and Development,edited by Edith Mathiowitz, Donald E. Chickering III, and Claus-Michael Lehr99. Protein Formulation and Delivery, edited by Eugene J. McNally100. New Drug Approval Process: Third Edition, The Global Challenge, edited by Richard A. Guarino101. Peptide and Protein Drug Analysis, edited by Ronald E. Reid102. Transport Processes in Pharmaceutical Systems, edited by Gordon L. Amidon, Ping I. Lee,and Elizabeth M. Topp103. Excipient Toxicity and Safety, edited by Myra L. Weiner and Lois A. Kotkoskie104. The Clinical Audit in Pharmaceutical Development, edited by Michael R. Hamrell105. Pharmaceutical Emulsions and Suspensions, edited by Francoise Nielloud and Gilberte Marti-Mestres106. Oral Drug Absorption: Prediction and Assessment, edited by Jennifer B. Dressman and Hans Lennerns107. Drug Stability: Principles and Practices, Third Edition, Revised and Expanded, edited by Jens T. Carstensen and C. T. Rhodes108. Containment in the Pharmaceutical Industry, edited by James P. Wood109. Good Manufacturing Practices for Pharmaceuticals: A Plan for Total Quality Control from Manufacturer to Consumer, Fifth Edition, Revised and Expanded, Sidney H. Willig110. Advanced Pharmaceutical Solids, Jens T. Carstensen111. Endotoxins: Pyrogens, LAL Testing, and Depyrogenation, Second Edition, Revised and Expanded, Kevin L. Williams112. Pharmaceutical Process Engineering, Anthony J. Hickey and David Ganderton113. Pharmacogenomics, edited by Werner Kalow, Urs A. Meyer and Rachel F. Tyndale114. Handbook of Drug Screening, edited by Ramakrishna Seethala and Prabhavathi B. Fernandes115. Drug Targeting Technology: Physical Chemical Biological Methods, edited by Hans Schreier116. DrugDrug Interactions, edited by A. David Rodrigues117. Handbook of Pharmaceutical Analysis, edited by Lena Ohannesian and Anthony J. Streeter118. Pharmaceutical Process Scale-Up, edited by Michael Levin119. Dermatological and Transdermal Formulations, edited by Kenneth A. Walters120. Clinical Drug Trials and Tribulations: Second Edition, Revised and Expanded,edited by Allen Cato, Lynda Sutton, and Allen Cato III121. Modern Pharmaceutics: Fourth Edition, Revised and Expanded, edited by Gilbert S. Bankerand Christopher T. Rhodes122. Surfactants and Polymers in Drug Delivery, Martin Malmsten123. Transdermal Drug Delivery: Second Edition, Revised and Expanded, edited by Richard H. Guy and Jonathan Hadgraft124. Good Laboratory Practice Regulations: Second Edition, Revised and Expanded, edited by Sandy WeinbergDK3090_half-series-title.qxd 9/9/05 10:25 AM Page F125. Parenteral Quality Control: Sterility, Pyrogen, Particulate, and Package Integrity Testing:Third Edition, Revised and Expanded, Michael J. Akers, Daniel S. Larrimore,and Dana Morton Guazzo126. Modified-Release Drug Delivery Technology, edited by Michael J. Rathbone, Jonathan Hadgraft, and Michael S. Roberts127. Simulation for Designing Clinical Trials: A Pharmacokinetic-Pharmacodynamic ModelingPerspective, edited by Hui C. Kimko and Stephen B. Duffull128. Affinity Capillary Electrophoresis in Pharmaceutics and Biopharmaceutics, edited by Reinhard H. H. Neubert and Hans-Hermann Rttinger129. Pharmaceutical Process Validation: An International Third Edition, Revised and Expanded, edited by Robert A. Nash and Alfred H. Wachter130. Ophthalmic Drug Delivery Systems: Second Edition, Revised and Expanded, edited by Ashim K. Mitra131. Pharmaceutical Gene Delivery Systems, edited by Alain Rolland and Sean M. Sullivan132. Biomarkers in Clinical Drug Development, edited by John C. Bloom and Robert A. Dean133. Pharmaceutical Extrusion Technology, edited by Isaac Ghebre-Sellassie and Charles Martin134. Pharmaceutical Inhalation Aerosol Technology: Second Edition, Revised and Expanded,edited by Anthony J. Hickey135. Pharmaceutical Statistics: Practical and Clinical Applications, Fourth Edition, Sanford Bolton and Charles Bon136. Compliance Handbook for Pharmaceuticals, Medical Devices, and Biologics, edited by Carmen Medina137. Freeze-Drying/Lyophilization of Pharmaceutical and Biological Products: Second Edition,Revised and Expanded, edited by Louis Rey and Joan C. May138. Supercritical Fluid Technology for Drug Product Development, edited by Peter York, Uday B. Kompella, and Boris Y. Shekunov139. New Drug Approval Process: Fourth Edition, Accelerating Global Registrations,edited by Richard A. Guarino140. Microbial Contamination Control in Parenteral Manufacturing, edited by Kevin L. Williams141. New Drug Development: Regulatory Paradigms for Clinical Pharmacologyand Biopharmaceutics, edited by Chandrahas G. Sahajwalla142. Microbial Contamination Control in the Pharmaceutical Industry, edited by Luis Jimenez143. Generic Drug Product Development: Solid Oral Dosage Forms, edited by Leon Shargel and Izzy Kanfer144. Introduction to the Pharmaceutical Regulatory Process, edited by Ira R. Berry145. Drug Delivery to the Oral Cavity: Molecules to Market, edited by Tapash K. Ghosh and William R. Pfister146. Good Design Practices for GMP Pharmaceutical Facilities, edited by Andrew Signore and Terry Jacobs147. Drug Products for Clinical Trials, Second Edition, edited by Donald Monkhouse, CharlesCarney, and Jim Clark148. Polymeric Drug Delivery Systems, edited by Glen S. Kwon149. Injectable Dispersed Systems: Formulation, Processing, and Performance, edited by Diane J. Burgess150. Laboratory Auditing for Quality and Regulatory Compliance, Donald Singer, Raluca-Ioana Stefan, and Jacobus van Staden151. Active Pharmaceutical Ingredients: Development, Manufacturing, and Regulation, edited by Stanley NusimDK3090_half-series-title.qxd 9/9/05 10:25 AM Page G152. Preclinical Drug Development, edited by Mark C. Rogge and David R. Taft153. Pharmaceutical Stress Testing: Predicting Drug Degradation, edited by Steven W. Baertschi154. Handbook of Pharmaceutical Granulation Technology: Second Edition, edited by Dilip M. Parikh155. Percutaneous Absorption: DrugsCosmeticsMechanismsMethodology, Fourth Edition,edited by Robert L. Bronaugh and Howard I. Maibach156. Pharmacogenomics: Second Edition, edited by Werner Kalow, Urs A. Meyer and Rachel F. Tyndale157. Pharmaceutical Process Scale-Up, Second Edition, edited by Lawrence Block158. Microencapsulation: Methods and Industrial Applications, Second Edition, edited by Simon BenitaDK3090_half-series-title.qxd 9/9/05 10:25 AM Page HMicroencapsulationMethods and Industrial ApplicationsSecond Editionedited bySimon BenitaHebrew University of JerusalemIsraelNew York LondonDK3090_half-series-title.qxd 9/9/05 10:25 AM Page iPublished in 2006 byCRC PressTaylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742 2006 by Taylor & Francis Group, LLCCRC Press is an imprint of Taylor & Francis GroupNo claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1International Standard Book Number-10: 0-8247-2317-1 (Hardcover) International Standard Book Number-13: 978-0-8247-2317-0 (Hardcover) Library of Congress Card Number 2005052195This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted withpermission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publishreliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materialsor for the consequences of their use.No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, orother means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any informationstorage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com(http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. Fororganizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged.Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only foridentification and explanation without intent to infringe.Library of Congress Cataloging-in-Publication DataMicroencapsulation : methods and industrial applications / edited by Simon Benita. -- 2nd ed.p. cm. -- (Drugs and the pharmaceutical sciences ; v. 158)Includes bibliographical references and index.ISBN-13: 978-0-8247-2317-0 (alk. paper)ISBN-10: 0-8247-2317-1 (alk. paper)1. Microencapsulation. I. Benita, Simon, 1947- . II. Series.[DNLM: 1. Drug Compounding QV 778 M6258 2005]RS201.C3M27 2005615'.19--dc22 2005052195Visit the Taylor & Francis Web site at http://www.taylorandfrancis.comand the CRC Press Web site at http://www.crcpress.comTaylor & Francis Group is the Academic Division of Informa plc.DK3090_Discl.fm Page 1 Monday, September 12, 2005 10:36 AMPreface to the Second EditionPrior to writing of the preface for the second edition, I read the preface of the rstedition published a decade ago. The assumptions that research, development, andsales of drug delivery systems would intensify in the following years were fullyveried and even exceeded expectations. As far as particulate delivery systems areconcerned, the research and development has been moving from the micro- to thenano-size scale. There is no doubt that microparticulate controlled delivery systemsmainly for topical and oral administration have been successfully exploited by thecosmetic and pharmaceutical industry respectively. However, the pharmaceuticalindustry is facing an uncertain future in which high clinical development costscoupled with declining drug discovery success rates are decreasing the ow of newproducts in the R&D pipeline. Experts are now recommending that pharmaceuticalcompanies move from the blockbuster model to a more extensive product portfoliomodel that focuses on diseases with insufcient therapies mainly in specic popula-tions such as the aging population. Furthermore, investigators are attempting toreformulate and add new indications to existing blockbuster drugs to maintain a rea-sonable scientic and economic growth rate. I believe that scientists have achievedremarkable successes in the eld of oral delivery. There are practical solutions toimproving the oral bioavailability of poorly absorbed lipophilic and hydrophobicdrugs. Oral controlled microparticulate systems have succeeded in maintainingadequate and effective plasma levels over prolonged periods of time by controllingdrug release following oral administration. However, there are still signicant unmetmedical needs in target diseases such as cancer, autoimmune disorders, maculardegeneration and Alzheimers disease. Most of the active ingredients used to treatthese severe diseases can be administered only through the parenteral route. Indeed,molecular complexity associated with drugs and inaccessibility of most pharmaco-logical targets are major constraints and the main reasons behind the increased inter-est and expanding research on nanodelivery systems, which can carry drugs directlyto their site of action. Thus, drug targeting has evolved as the most desirable butelusive goal in the science of drug delivery. Drug targeting offers enormous advan-tages but is highly challenging and extremely complicated. A better understanding ofthe physiological barriers a drug needs to overcome should provide the pharmaceu-tical scientist with the information and tools needed to develop successful designs fordrug targeting delivery systems. Optimal pharmacological responses require bothspatial placement of the drug molecules and temporal control at the site of action.Many hurdles and drawbacks still need to be overcome through intensive effortsand concentrated interdisciplinary scientic collaboration to reach the desired goals.iiiThe second edition of Microencapsulation, Methods and Industrial Appli-cations comprises 11 expanded and revised chapters and 12 new chapters that reectthe evolution of this discipline in the past decade.It is my hope that this multi-authored second edition of Microencapsulation,Methods and Industrial Applications will assist and enrich the readers in under-standing the diverse types of particulate systems currently available or under develop-ment as well as highlight possible applications in the future.I am deeply grateful to Ms. Madelyn Segev, the secretary of the PharmaceuticsDepartment of the School of Pharmacy of The Hebrew University of Jerusalem whospared no effort to help me in bringing this project to fruition.To Einat, Yair and MaytalSimon Benitaiv Preface to the Second EditionPreface to the First EditionResearch, development, and sales of drug-delivery systems are increasing at a rapidpace throughout the world. This worldwide trend will intensify in the next decade ascuts in public health expenses demand lower costs and higher efcacy. To meet thisdemand, many efcient drugs currently in use will be reformulated within deliverysystems that can be value-added for optimal molecular activity. In addition to thehealth sector, the cosmetic, agricultural, chemical, and food industries operate inan open marketplace where free and aggressive competition demands novel coatingtechniques with enhanced effectiveness at the lowest possible cost. Currently, micro-encapsulation techniques are most widely used in the development and production ofimproved drug- and food-delivery systems. These techniques frequently result inproducts containing numerous variably coated particles. The exact number of particlesneeded to form a single administered dose varies as a function of the nal particle sizeand can lie in either the micro- or nanometer size range for micro- and nanoparticulatedelivery systems, respectively.The microparticulate delivery systems include mainly pellets, microcapsules,microspheres, lipospheres, emulsions, and multiple emulsions. The nanoparticulatedelivery systems include mainly lipid or polymeric nanoparticles (nanocapsulesand nanospheres), microemulsions, liposomes, and nonionic surfactant vesicles(niosomes).Generally, the microparticulate delivery systems are intended for oral and topi-cal use. Different types of coated particles can be obtained depending on the coatingprocess used. The particles can be embedded within a polymeric or proteinic matrixnetwork in either a solid aggregated state or a molecular dispersion, resulting in theformulation of microspheres. Alternatively, the particles can be coated by a solidiedpolymeric or proteinic envelop, leading to the formation of microcapsules. Theprole and kinetic pattern governing the release rate of the entrapped active substancefrom the dosage form depend on the nature and morphology of the coated particles,which need to be established irrespective of the manufacturing method used.Microencapsulation techniques are normally used to enhance material stabi-lity, reduce adverse or toxic effects, or extend material release for different applica-tions in various elds of manufacturing.Until now, the use of some interesting and promising therapeutic substanceshas been limited clinically because of their restrictive physico-chemical properties,which have required frequent administration. It is possible that these substancesmay become more widely used in a clinical setting if appropriate microencapsulationtechniques can be designed to overcome their intrinsic conveniences.vInvestigators and pharmacologists have been trying to develop delivery systemsthat allow the fate of a drug to be controlled and the optimal drug dosage to arriveat the site of action in the body by means of novel microparticulate dosage forms.During the past two decades, researchers have succeeded in part in controlling thedrug-absorption process to sustain adequate and effective plasma drug levels overa prolonged period of time by designing delayed- or controlled-release microparticu-late-delivery systems intended for either oral or parenteral administration.The ultimate objective of microparticulate-delivery systems is to control andextend the release of the active ingredient from the coated particle without attempt-ing to modify the normal biofate of the active molecules in the body after adminis-tration and absorption. The organ distribution and elimination of these moleculeswill not be modied and will depend only on their physicochemical properties. Onthe other hand, nanoparticulate-delivery systems are usually intended for oral, par-enteral, ocular, and topical use, with the ultimate objective being the alternation ofthe pharmacokinetic prole of the active molecule.In the past decade, ongoing efforts have been made to develop systems or drugcarrier capable of delivering the active molecules specically to the intended targetorgan, while increasing the therapeutic efcacy. This approach involves modifyingthe pharmacokinetic prole of various therapeutic classes of drugs through theirincorporation in colloidal nanoparticulate carriers in the submicron size range suchas liposomes and nanoparticles. These site-specic delivery systems allow an effectivedrug concentration to be maintained for a longer interval in the target tissue andresult in decreased side effects associated with lower plasma concentrations in theperipheral blood. Thus, the principle of drug targeting is to reduce the total amountof drug administered, while optimizing its activity. It should be mentioned that thescientic community was skeptical that such goals could be achieved, since hugeinvestments of funds and promising research studies have in many cases resultedin disappointing and nonlucrative results and have also been slow in yielding success-fully marketed therapeutic nanoparticulate dosage forms. With the recent approvalby health authorities of a few effective nanoparticulate products containing antifun-gal or cytotoxic drugs, interest in colloidal drug carriers has been renewed.A vast number of studies and review as well as several books have been devotedto the development, characterization, and potential applications of specic micro-particulate- and nanoparticulate-delivery systems. No encapsulation process devel-oped to date has been able to produce the full range of capsules desired bypotential capsule users. Few attempts have been made to present and discuss in asingle book the entire size range of particulate dosage forms covered in this book.The general theme and purpose here are to provide the reader with a current andgeneral overview of the existing micro- and nanoparticulate-delivery systems andto emphasize the various methods of preparation, characterization, evaluation,and potential applications in various areas such as medicine, pharmacy, cosmetol-ogy, and agriculture. The systematic approach used in presenting the various parti-culate systems should facilitate the comprehension of this increasingly complex eldand clarify the main considerations involved in designing, manufacturing, characteri-zing, and evaluating a specic particulate-delivery system for a given application orpurpose. Thus, the chapters, which have been contributed by leading authorities inthe eld, are arranged logically according to the methods of preparation, characteri-zation, and applications of the various particulate-delivery systems.The rst chapter is by C. Thies, a renowned scientist in the eld of microencap-sulation techniques. To provide an idea of which process is most appropriate for avi Preface to the First Editionspecic application, the general principles of several microencapsulation processesare summarized and reviewed. This chapter focuses primarily on processes that haveachieved signicantly commercial use. S. Magdassi and Y. Vinetsky present an inter-esting technique of oil-in-water emulsion microencapsulation by proteins followingadsorption of the protein molecules onto the oilwater interface. J. P. Benoit andDrs. H. Marchais, H. Rolland, and V. Vande Velde have contributed a chapter onadvances in the production technology of biodegradable microspheres. This chapterdeals mainly with the preparation and use of microspheres. The potential of thevarious technologies addressed is also discussed, with an emphasis on marketed pro-ducts or those products currently under clinical evaluation. A. Markus demonstratesin his chapter the importance of applying microencapsulation techniques in the designof controlled-release pesticide formulations to meet the multifaceted demands ofefcacy, suitability to mode of application, and minimal damage to the environment.The nanoparticulate-delivery systems are introduced by a chapter, authored bymyself, B. Magenheim, and P. Wehrle, that explains factorial design in the develop-ment of nanoparticulate systems. This chapter illustrates the application of the experi-mental design technique not only for optimization but also for elucidation of themechanistic aspects of nanoparticle formation by spontaneous emulsication.The second part of the book, which focuses on the evaluation and characteriza-tion of the various particulate-delivery systems, starts with an important chapter onmicrospheres morphology by J. P. Benoit and C. Thies. The chapter helps to clarifydenitions and differences, which are very often confused. In addition, the chapterillustrates how morphology can be characterized by using different techniques.C. Washington provides his valuable expertise in the presentation of the variouskinetic models used to characterize drug-release proles from ensembles or popula-tion of microparticulate-delivery systems. It is worth noting that the release mechan-ism of a drug from multiparticulate systems such as microcapsules or microspherescannot be identied by a study of global release proles, since it has been shown thatoverall or cumulative release proles form ensembles of microcapsules are entirelydifferent from those of single microcapsules. The discrepancy arises from the hetero-geneous distribution of the parameters determining release behavior in individualmicrocapsules, which is beyond the scope of the present chapter. The followingchapter, by P. Couvreur, G. Couarraze, J. -P. Devissaguet, and F. Puisieux, presentsa very detailed explanation of the preparation and characterization of nanoparticles.The authors rst clearly dene the morphology of nanocapsules and nanospheres,providing the background, information, and guidelines for choosing the appropriatemethods for a given drug to be encapsulated.K. Westesen and B. Siekmann have contributed an important chapter onbiodegradable colloidal drugcarrier systems based on solid lipids. These new colloi-dal carriers different from the other well-known and widely investigated lipidic col-loidal carriers, including liposomes, lipoproteins, and lipid or submicron oil-in-wateremulsions by exhibiting a solid physical state as opposed to the liquid or liquid crys-talline state of the above-mentioned and well-known lipidic colloidal carriers. Theauthors present different methods of preparation and point out the advantages of thenovel dosage forms such as biodegradability, biocompatibility, ease of manufacture,lack of drug leakage, and sustained drug release. Despite three decades of intensiveresearch on liposomes as drug-delivery systems, the number of systems that haveundergone clinical trials and become products on the market is quite modest. Eventhough there have been few successes with liposomes, the need for drug-delivery sys-tems is as acute as ever, and the potential that liposomes hold, although somewhatPreface to the First Edition viitarnished, has not been substantially diminished according to R. Margalit andN. Yerushalmi. An interesting and original approach is presented in their chapter onthe pharmaceutical aspects of liposomes. Propositions are presented on how at leastsome of the hurdles in research and development can be overcome and in furtheringthe substantial strides that have been made in advancing liposomes fromthe laboratoryto the clinic. An ingenious solution on how the drawbacks of liposomes in vivo can beovercome is presented by D. Lasic in the chapter on stealth liposomes. He explains howthe stability of liposomes in liposomicidal environments of biological systems presenteda great challenge, which was only recently solved by coupling polyethylene glycol to thelipid molecules. An example of the potential of niosomes (a colloidal vesicular systemprepared from nonionic surfactants) for the topical application of estradiol is contri-buted by D. A. van Hal and J. A. Bouwstra, and H. E. Junginger. Niosomes have beenshown to increase the penetration of a drug through human stratum corneum by afactor of 50 as compared with estradiol saturated in phosphate buffer solution, makingthis colloidal carrier promising for the transdermal delivery of drugs.In the third part of the book, the potential applications of the various particu-late-delivery systems are presented. The methods of preparation of microcapsules byinterfacial polymerization and interfacial complexation and their applications arediscussed by T. Whateley, an extremely knowledgeable scientist in this eld. Thefast-growing eld of lipid microparticulate-delivery systems, particularly lipospheres,is explained and discussed by A. J. Domb, L. Bergelson, and S. Amselem. Lipo-spheres represent a new type of fat-based encapsulation technology developed forthe parenteral delivery of drugs and vaccines and the topical administration ofbioactive compounds. In their comprehensive and exhaustive chapter, N. Garti andA. Aserin underline the potential of pharmaceutical application of emulsions, multipleemulsions, and microemulsions, and emphasize the progress made in the last 15 yearsin understanding mechanism of stabilization of these promising liquid dispersed-delivery systems that open new therapeutic possibilities.J.-C. Leroux and E. Doelker and R. Gurny in their chapter on the use of drug-loaded nanoparticles in cancer chemotherapy cover the developments and progressmade in the delivery of anticancer drugs coupled to nanoparticles, and the interac-tions of the latter with neoplastic cells and tissues. This is probably the most promis-ing and encouraging application of nanoparticles and by far the most advancedin the process of development into a viable commercial pharmaceutical product.G. Redziniak and P. Perrier have contributed a chapter on the cosmetic applicationof liposomes that have been successfully exploited over the last decade. To completethe whole range of applications of capsular products, a nal chapter, by M. Seiller,M.-C. Martini, and myself, discusses cosmetic uses of vesicular particulate-deliverysystems. Cosmetics are denitely the largest market, as manufacturers have demon-strated that marketed cosmetic products containing these vesicular carriers andtested by dermatologists improve cutaneous hydration and skin texture, increaseskin glow, and decrease wrinkle depth. It is not taken for granted that liposomesand other vesicular carriers represent a major step in cosmetics formulation.However, this eld requires numerous research studies coupled with strict controls.It is my hope that the scientic information contained herein will modestlycontribute to a better understanding of the various particulate systems of all sizesthat are now available and to an improved comprehension of their current andpotential applications.Simon Benitaviii Preface to the First EditionContentsPreface to the Second Edition . . . . iiiPreface to the First Edition . . . . vContributors . . . . xvPART I: METHODS OF ENCAPSULATION AND ADVANCES INPRODUCTION TECHNOLOGY1. Biodegradable Microspheres: Advances inProduction Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Fre de ric Tewes, Frank Boury, and Jean-Pierre BenoitIntroduction . . . . 1Techniques Using Organic Solvents . . . . 2Techniques Without Organic Solvents . . . . 8References . . . . 412. Advances in the Technology for Controlled-ReleasePesticide Formulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Arie Markus and Charles LinderIntroduction . . . . 55Standard Microencapsulation Processes forPesticides . . . . 59Advances in Encapsulation Technologies . . . . 67Quality Control . . . . 71Case Study: De-Bugger. . . . 75Summary . . . . 75References . . . . 763. Multiparticulate Pulsatile Drug Delivery Systems . . . . . . . . . . . . . 79Till Bussemer and Roland BodmeierIntroduction . . . . 79Pulsatile Systems . . . . 83Site-Specic Systems . . . . 84Time-Controlled Pulsatile Systems . . . . 86ixMultiparticulate Systems . . . . 87Outlook . . . . 94References . . . . 944. Microencapsulation Techniques for Parenteral Depot Systems andTheir Application in the Pharmaceutical Industry . . . . . . . . . . . . . 99Thomas Kissel, Sascha Maretschek, Claudia Packha user,Julia Schnieders, and Nina SeidelIntroduction . . . . 99Biodegradable Polymers . . . . 100Phase Separation and Coacervation . . . . 103W/O/W-Double Emulsion Technique . . . . 106Spray Drying . . . . 113Conclusion . . . . 118References . . . . 1185. Coupling Methods to Obtain Ligand-Targeted Liposomesand Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123Leila Bossy-Nobs, Franz Buchegger, Robert Gurny, and Eric Alle mannIntroduction . . . . 123Liposomal Modication Techniques . . . . 124Labeling Polymeric Nanoparticles with Ligands . . . . 138How to Choose the Coupling Method . . . . 141Concluding Remarks . . . . 142References . . . . 1426. Industrial Technologies and Scale-Up . . . . . . . . . . . . . . . . . . . . . 149Franc ois Puel, Ste phanie Brianc on, and Hatem FessiIntroduction . . . . 149Emulsication Processes . . . . 152Scale-Up Approach: The Case of Emulsication . . . . 164ApplicationsExamples . . . . 167Summary . . . . 178Notations . . . . 178References . . . . 179PART II: EVALUATION AND CHARACTERIZATION OFMICRO- AND NANOPARTICULATE DRUG DELIVERY SYSTEMS7. Drug Release from Microparticulate Systems . . . . . . . . . . . . . . . 183Shicheng Yang and Clive WashingtonIntroduction . . . . 183Measurement of Drug Release . . . . 183Mechanisms of Drug Release . . . . 186Drug Release Kinetic Models . . . . 188x ContentsEmpirical Models and Comparison of Drug Release Proles . . . . 198In VitroIn Vivo Correlation . . . . 203Summary . . . . 204References . . . . 2058. Manufacture, Characterization, and Applications ofSolid Lipid Nanoparticles as Drug Delivery Systems . . . . . . . . . . 213Heike Bunjes and Britta SiekmannIntroduction: The Rationale of Using Biodegradable,Nanoparticulate Solid Lipids in Drug Delivery . . . . 213Manufacturing Methods for Lipid NanoparticleSuspensions . . . . 216Physicochemical Characterization of Colloidal LipidSuspensions and Nanoparticles . . . . 230Applications in Drug Delivery . . . . 242Conclusions . . . . 255References . . . . 2579. Amphiphilic Cyclodextrins and Microencapsulation . . . . . . . . . . . 269Erem Memisog lu-Bilensoy, A. Atilla Hincal, Ame lie Bochot,Laury Trichard, and Dominique Duche neIntroduction . . . . 269Cyclodextrins and Derivatives . . . . 270Amphiphilic Cyclodextrin Nanoparticles . . . . 278Conclusion . . . . 291References . . . . 29110. Lipospheres for Controlled Delivery of Substances . . . . . . . . . . . . 297Abraham J. DombIntroduction . . . . 297Preparation of Lipospheres . . . . 298Physical Characterization of Lipospheres . . . . 299Applications of Lipospheres . . . . 302Summary . . . . 314References . . . . 31511. Pharmaceutical Aspects of Liposomes: Academic and IndustrialResearch and Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317Rimona Margalit and Noga YerushalmiIntroduction . . . . 317Liposomes: Denition, Needs for, and Outline of theirAdvantages and Drawbacks . . . . 318Selection of the Liposome Type/Species: Views andCriteria from Academic and Industrial Researchand Their Proposed Integration . . . . 323Contents xiTargeted/Modied Liposomes: An Interesting and ExcitingScientic Tool, But Can They Be Made into Products(Especially Immunoliposomes)? . . . . 326Liposomes as a Sterile, Pyrogen-Free System withPharmaceutically Acceptable Shelf-Life, Stability,and Dosage Forms . . . . 330Liposome Characteristics (Percentage of Encapsulation,Kinetics of Release, Biological Activity)In BasicResearch and in Quality Assurance . . . . 333Summary and Prospects . . . . 340References . . . . 34012. Microemulsions for Solubilization and Delivery ofNutraceuticals and Drugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345Nissim Garti and Abraham AserinThe Rationale . . . . 345Microemulsions as Nanovehicles . . . . 348Part IMicroemulsion Preparation and Microstructures . . . . 349Part IIPotential Applications . . . . 385Final Remarks . . . . 414References . . . . 416PART III: APPLICATIONS OF PARTICULATEDELIVERY SYSTEMS13. Self-Emulsifying Oral Lipid-Based Formulations forImproved Delivery of Lipophilic Drugs . . . . . . . . . . . . . . . . . . . . 429Jean-Se bastien Garrigue, Gre gory Lambert, and Simon BenitaDenition . . . . 429Introduction . . . . 430Drug Delivery Issues . . . . 430Composition of SEDDS . . . . 433Characterization of SEDDS . . . . 444Biopharmaceutical Aspects . . . . 448The Story of Oral Cyclosporin A . . . . 466The Oral Paclitaxel Challenge . . . . 468Future and Prospects . . . . 469References . . . . 47014. Recent Advances in Heparin Delivery . . . . . . . . . . . . . . . . . . . . . 481Nathalie Ubrich and Philippe MaincentIntroduction . . . . 481Blood and Mechanism of Action of Heparins . . . . 482Evaluation of Heparin Efciency . . . . 483Oral Delivery of Heparins . . . . 483Conclusion . . . . 516References . . . . 516xii Contents15. Particulate Systems for Oral Drug Delivery . . . . . . . . . . . . . . . . 521Mara Jose Blanco-Preto and Florence DelieIntroduction . . . . 521Absorption of Polymeric Particulates fromthe GI Tract . . . . 522Use of Polymeric Particles for Oral Administration . . . . 527Conclusions . . . . 552References . . . . 55316. Vesicles as a Tool for Dermal and Transdermal Delivery . . . . . . . 563P. L. Honeywell-Nguyen and J. A. BouwstraDermal and Transdermal Drug Delivery . . . . 563The Skin Barrier Function . . . . 564Vesicles as Skin Delivery Systems . . . . 566Elastic Vesicles . . . . 572References . . . . 58017. Lipid and Polymeric Colloidal Carriers for OcularDrug Delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587Simon Benita and S. TamilvananIntroduction . . . . 587Topically Treated Ocular Pathologies . . . . 589Lipid and Polymeric Colloidal Carriers: Descriptionand Classication . . . . 594O/W Submicron Emulsions . . . . 596Microemulsions . . . . 605Multiple Emulsions . . . . 607Nanoparticles . . . . 608Nanocapsules . . . . 614Future Directions in Ocular Drug Delivery Using Lipidand Polymeric Colloidal Carriers . . . . 617References . . . . 61718. The Use of Drug-Loaded Nanoparticles inCancer Chemotherapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625Jean-Christophe Leroux, Angelica Vargas, Eric Doelker,Robert Gurny, and Florence DelieIntroduction . . . . 625In Vitro Uptake of NP by Tumoral Cells . . . . 626Distribution and Pharmacokinetics of AnticancerDrugs Coupled to NP . . . . 639In Vivo Activity and Toxicity of AnticancerDrugs Coupled to NP . . . . 650Concluding Remarks . . . . 661References . . . . 662Contents xiii19. Development of 5-FULoaded PLGA Microparticles for theTreatment of Glioblastoma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673Nathalie Faisant, Jean-Pierre Benoit, and Philippe MeneiIntroduction . . . . 673Microsphere Formulation and Development . . . . 674Preclinical Trials . . . . 678Application to Glioma Therapy After Tumor Resection:Phase III and IIB Studies . . . . 682Stereotaxic Implantation in Malignant Glioma:Phase I Study . . . . 684Conclusion . . . . 685References . . . . 68620. Nanoparticles as Drug Delivery Systems for the Brain . . . . . . . . . 689Jo rg KreuterIntroduction . . . . 689Drug Delivery to the Brain with Nanoparticles . . . . 690Long Circulating Nanoparticles for Brain Drug Delivery . . . . 697Stability of Nanoparticles for Brain Delivery Upon Storage . . . . 699Mechanism of Nanoparticle-Mediated Drug Transportto the Brain . . . . 699Conclusions . . . . 702References . . . . 70321. Cosmetic Applications of Colloidal Delivery Systems . . . . . . . . . . 707Simon Benita, Marie-Claude Martini, Anne-Marie Orecchioni, andMonique SeillerIntroduction . . . . 707Types of Vesicular Delivery Systems . . . . 708Composition . . . . 715Production . . . . 720Characterization . . . . 727Stability . . . . 731Cosmetic Uses . . . . 732Conclusion . . . . 741References . . . . 741Index . . . . 749xiv ContentsContributorsEric Allemann School of Pharmaceutical Sciences (EPGL), University of Geneva,Quai Ernest-Ansermet, Geneva, SwitzerlandAbraham Aserin Casali Institute of Applied Chemistry, The Hebrew Universityof Jerusalem, Jerusalem, IsraelSimon Benita Department of Pharmaceutics, School of Pharmacy, Facultyof Medicine, The Hebrew University of Jerusalem, Jerusalem, IsraelJean-Pierre Benoit INSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Angers, FranceMar a Jose Blanco-Pr eto Centro Galenico, Farmacia y Tecnolog a Farmaceutica,Universidad de Navarra, Pamplona, SpainAmelie Bochot Universite Paris-Sud, Faculte de Pharmacie, Chatenay-MalabryCedex, FranceRoland Bodmeier College of Pharmacy, Freie Universitat Berlin, Kelchstr,Berlin, GermanyLeila Bossy-NobsGeneva, Quai Ernest-Ansermet, Geneva, SwitzerlandFrank Boury INSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Angers, FranceJ. A. Bouwstra Leiden/Amsterdam Center for Drug Research, Leiden University,Einsteinweg, RA Leiden, The NetherlandsStephanie Briancon LAGEP UMR CNRS 5007 and Laboratoire de GeniePharmacotechnique et Biogalenique, Universite Claude Bernard Lyon 1,Lyon, FranceFranz Buchegger Service of Nuclear Medicine, University Hospital of Geneva,Rue Micheli-du-Crest, Geneva, SwitzerlandxvSchool of Pharmaceutical Sciences (EPGL), University ofHeike Bunjes Department of Pharmaceutical Technology, Institute of Pharmacy,Friedrich Schiller University Jena, Jena, GermanyTill Bussemer Sano-Aventis Deutschland GmbH, Pharmaceutical SciencesDepartment Industriepark Ho chst, Frankfurt am Main, GermanyFlorence Delie School of Pharmaceutical Sciences (EPGL), University of Geneva,Quai Ernest-Ansermet, Geneva, SwitzerlandEric Doelker School of Pharmaceutical Sciences (EPGL), University of Geneva,Quai Ernest-Ansermet, Geneva, SwitzerlandAbraham J. Domb Department of Medicinal Chemistry and Natural Products,School of Pharmacy-Faculty of Medicine and the David R. Bloom Center forPharmacy, Alex Grass Center for Drug Design and Synthesis, The HebrewUniversity of Jerusalem, Jerusalem, IsraelDominique Duchene Universite Paris-Sud, Faculte de Pharmacie,Chatenay-Malabry Cedex, FranceNathalie Faisant INSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Immeuble IBT, Angers, FranceHatem Fessi LAGEP UMR CNRS 5007 and Laboratoire de GeniePharmacotechnique et Biogalenique, Universite Claude Bernard Lyon 1,Lyon, FranceJean-Sebastien Garrigue Novagali Pharma S.A., Batiment Genavenir IV,Evry, FranceNissim Garti Casali Institute of Applied Chemistry, The Hebrew Universityof Jerusalem, Jerusalem, IsraelRobert GurnyQuai Ernest-Ansermet, Geneva, SwitzerlandA. Atilla Hincal Hacettepe University, Faculty of Pharmacy, Department ofPharmaceutical Technology, Ankara, TurkeyP. L. Honeywell-Nguyen Leiden/Amsterdam Center for Drug Research, LeidenUniversity, Einsteinweg, RA Leiden, The NetherlandsThomas Kissel Department of Pharmaceutics and Biopharmacy,Philipps-University of Marburg, Ketzerbach, Marburg, GermanyJorg Kreuter Institut fu r Pharmazeutische Technologie, Johann WolfgangGoethe-Universitat Frankfurt, Frankfurt/Main, GermanyGregory Lambert Novagali Pharma S.A., Batiment Genavenir IV,Evry, Francexvi ContributorsSchool of Pharmaceutical Sciences (EPGL), University of Geneva,Jean-Christophe Leroux University of Montreal, Centre ville, Montreal,Quebec, CanadaCharles Linder The Institutes for Applied Research, Ben-Gurion Universityof the Negev, Beer-Sheva, IsraelPhilippe Maincent INSERM U734EA 3452, Laboratoire de PharmacieGalenique, Faculte de Pharmacie, Nancy, Cedex, FranceSascha Maretschek Department of Pharmaceutics and Biopharmacy, Philipps-University of Marburg, Ketzerbach, Marburg, GermanyRimona Margalit Department of Biochemistry, The George S. Wise Faculty of LifeSciences, Tel Aviv University, Tel Aviv, IsraelArie Markus The Institute of Chemisty and Chemical Technology, The Institutesfor Applied Research, Ben-Gurion University of the Negev, Beer-Sheva, IsraelMarie-Claude Martini Institut des Sciences Pharmaceutiques et Biologiques,Lyon, FranceErem Memisoglu-Bilensoy Hacettepe University, Faculty of Pharmacy,Department of Pharmaceutical Technology, Ankara, TurkeyPhilippe Menei INSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Immeuble IBT and Department of Neurosurgery, CHUAngers, Angers, FranceAnne-Marie Orecchioni Universite de Rouen, Rouen, FranceClaudia Packhauser Department of Pharmaceutics and Biopharmacy,Philipps-University of Marburg, Ketzerbach, Marburg, GermanyFrancois Puel LAGEP UMR CNRS 5007, Universite Claude Bernard Lyon 1,Lyon, FranceJulia Schnieders Department of Pharmaceutics and Biopharmacy,Philipps-University of Marburg, Ketzerbach, Marburg, GermanyNina Seidel Department of Pharmaceutics and Biopharmacy, Philipps-Universityof Marburg, Ketzerbach, Marburg, GermanyMonique Seiller Universite de Caen, Caen, FranceBritta Siekmann Ferring Pharmaceuticals A/S, Ferring International Center,Kay Fiskers Plads, Copenhagen, DenmarkS. Tamilvanan Department of Pharmaceutics, School of Pharmacy, Addis AbabaUniversity, Addis Ababa, Ethiopia and Department of Pharmaceutics, SchoolContributors xviiof Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem,Jerusalem, IsraelFrederic Tewes INSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Angers, FranceLaury Trichard Universite Paris-Sud, Faculte de Pharmacie, Chatenay-MalabryCedex, FranceNathalie Ubrich INSERM U734EA 3452, Laboratoire de Pharmacie Galenique,Faculte de Pharmacie, Nancy, Cedex, FranceAngelica Vargas School of Pharmaceutical Sciences (EPGL), University ofGeneva, Quai Ernest-Ansermet, Geneva, SwitzerlandClive Washington Pharmaceutical and Analytical Research and Development,AstraZeneca, Maccleseld Works, Hurdseld Industrial Estate, Maccleseld,Cheshire, U.K.Shicheng Yang KV Pharmaceutical Company, St. Louis, Missouri, U.S.A.Noga Yerushalmi Department of Biochemistry, The George S. Wise Facultyof Life Sciences, Tel Aviv University, Tel Aviv, Israelxviii Contributors1Biodegradable Microspheres: Advancesin Production TechnologyFrederic Tewes, Frank Boury, and Jean-Pierre BenoitINSERM U646, Ingenierie de la Vectorisation Particulaire,Universite dAngers, Angers, FranceINTRODUCTIONResearch to nd new or to improve microencapsulation techniques to process newlydiscovered active molecules is in constant progress because of the limitations of thecurrent pharmacopeia. The new active molecules found with the help of advancesin biotechnology and therapeutic science are more often peptides or proteins; theyare very active in small doses, sensitive to unfolding by heat or organic solvents,available only in small quantities, and very expensive. Additionally, many new mole-cules that are synthesized have poor solubility in aqueous media, and some of them,when used in their typical therapeutic concentrations, such as paclitaxel, also havepoor solubility in lipidic media.Besides this, the regulatory authorities, such as the U.S. Food and DrugAdministration (FDA), are restricting to greater degrees the amounts of additionalcomponents allowed such as organic solvents or tensioactive molecules.For these reasons, in designing of new techniques one must take into accountseveral new requirements: The stability and the biological activity of the drugshould not be affected during the microencapsulation process, yield and drug encap-sulation efciency should be high, microsphere quality and the drug release proleshould be reproducible within specied limits, microspheres should not exhibitaggregation or adherence, the process should be usable at an industrial scale, andthe residual level of organic solvent should be lower than the limit value imposedby the European Pharmacopeia.However, the commonly used techniques such as emulsicationsolventremoval, polymer phase separation, spray drying, and milling methods are not alwayssuitable in their original forms for these new requirements. Spray drying and millingcan thermally denature some compounds. Milling produces a broad size distribution.Emulsion/solvent removal techniques can denature proteins at the interfaces. Poly-mer phase separation, spray drying, and emulsication processes often lead toamounts of residual solvent that are higher than the upper authorized values. There-fore, modications to these processes or the development of new techniques is needed.PART I: METHODS OF ENCAPSULATION AND ADVANCES IN PRODUCTIONTECHNOLOGY1Near critical or supercritical uid techniques are promising and full some of the newrequirements.In this chapter, we present an overview of the existing techniques that usuallymake use of volatile solvents and we describe the improvements proposed to meetthe new requirements. We then present techniques that do not use volatile organicsolvents, with special attention to techniques using supercritical uids.TECHNIQUES USING ORGANIC SOLVENTSEmulsicationSolvent Removal ProcessesInitially, polymers are dissolved in a volatile organic solvent with low water miscibil-ity, such as dichloromethane (DCM) or chloroform. The drugs are then dissolved ordispersed in the polymer solution. This mixture is then emulsied in a large volumeof an aqueous phase containing tensioactive molecules such as poly(vinyl alcohol)(PVA), resulting in organic solvent droplets dispersed in a water phaseoil-in-water(O/W) emulsion. The emulsion is next subjected to solvent removal by either eva-poration or an extraction process in order to generate microspheres. These particlesare washed, collected by ltration, sieving, or centrifugation, and nally dried or lyo-philized to provide free-owing injectable microspheres.The two processes of solvent removal inuence microsphere size and morpho-logy. When the solvent is evaporated, the emulsion is maintained at reduced oratmospheric pressure under low agitation. If the drug molecules are volatile and/orhave a great afnity for the organic phase, they can be removed at the same time.During the extraction process, the emulsion is transferred into a large volume ofwater (with or without surfactant) or another quench medium, where the solventdiffuses out (1). The quenching medium must not make the polymer soluble andmust have a great afnity for the aqueous phase. It should be noted that the solventevaporation process is similar to the extraction method, in that the solvent must rstdiffuse out into the external aqueous dispersion medium before it can be removedfrom the system by evaporation (2). The rate of solvent removal inuences thecharacteristics of the microspheres. Rapid solvent removal leads to the formationof porous structures on the microsphere surface and to a hardening of the polymersin the amorphous state. Solvent removal by the extraction method is faster (generallyless than 30 min) than by the evaporation process and hence, the microspheres gen-erated by the former method are more porous and more amorphous (2).Hydrophilic MoleculesAnhydrous Emulsion. As described above, the O/W emulsication process isappropriate for encapsulating apolar drugs. It leads to poor encapsulation efciencyfor polar water-soluble drugs (1). The polar drugs can partition between the twophases. Consequently, besides low drug entrapment, hydrophilic drugs are oftendeposited on the microsphere surface (3). This induces an initial rapid release ofthe drug, known as the burst effect (1).Modications of the conventional O/W solvent removal method have been sug-gested to avoid these problems. One of these is the use of totally anhydrous systems.They are constituted from an organic volatile phase (acetonitrile, acetone), containingdrugs and polymers, emulsied in an immiscible oil (mineral or vegetable) or a non-volatile organic solvent containing a surfactant with a low hydrophilelipophile2 Tewes et al.balance (HLB) [oil-in-oil emulsion (O/O emulsion)] (4,5). Microspheres are nallyobtained by evaporation or extraction of the volatile solvent and washed in anothersolvent such as n-hexane to remove the oily dispersing media. This process essentiallyavoids the loss of drugs, being soluble in water, such as amino-alcohols, amino-acidsand peptides, proteins, cytostatics like cisplatin, or anti-inammatory drugs (49).Multiple Emulsions. Another modication that allows the encapsulation ofwater-soluble molecules is the formation of a water-in-organic solvent-in-water(W/O/W) emulsion (10). An aqueous solution of the drug (sometimes containinga viscosity builder and/or protein acting as a tensioactive agent and carrier) isadded to a volatile organic phase containing the polymers under intense shear (highpressure homogenizer, sonicator, etc.) to form a water-in-oil (W/O) emulsion. Thisemulsion is gently added under stirring into a large volume of water containingtensioactive molecules to form the W/O/W emulsion. The most commonly usedtensioactive agents are PVA and poly(vinyl pyrrolidone) (11,12). The emulsionis nally subjected to solvent removal either by evaporation or extraction. Thesolid microspheres obtained by this process are washed, collected, and dried orlyophilized.This technique has mainly been used for the encapsulation of peptides such asleuteinizing hormonereleasing hormone (LHRH) agonist (leuprolide acetate),somatostatin, proteins, and other hydrophilic molecules in poly(a-hydroxyacid)ssuch as poly(D,L-lactide) (DL-PLA), poly(D,L-lactide-co-glycolide) (PLGA), orpoly(L-lactide) (L-PLA) microparticles (1138).Schugens et al. (36) have shown that an increase in the molecular weight Mw ofL-PLA required the dilution of the polymer solution to prevent an exceedingly highviscosity, which led to formation of less stable primary emulsions and to moreporous solid microspheres. They also concluded that the crystallinity of L-PLAaffected the stability of the primary emulsion by exclusion of the internal aqueousdroplets from the L-PLA matrix. This exclusion adversely impacted the encapsula-tion efciency, and increased the microparticle porosity. Herrmann and Bodmeier(17) created microspheres composed of L-PLA, PLGA, or DL-PLA and found thatan increase in the volume fraction of the internal aqueous phase in the primary W/Oemulsion resulted in lower encapsulation efciency when it is made with DCM asorganic solvent. Crotts and Park (27) found that this increase induced the formationof pores in the shell layers of PLGA microspheres. Herrmann and Bodmeier (18)also showed that the addition of buffers or salts to the internal aqueous phaseresulted in porous L-PLA microspheres and lowered somatostatin encapsulationefciency. This is due to the increase of the difference of osmotic pressure betweenthe two aqueous phases, and the promotion of an inux of water from the externalphase toward the internal phase. The addition of salts to the external aqueousmedium resulted in the formation of a dense and homogeneous polymer matrix (32).This technique can induce an incomplete release of encapsulated protein asobserved with PLGA microspheres by Park and Lu (28) and Pean et al. (32). Parkand Lu determined that proteins were signicantly and irreversibly denatured andaggregated during the emulsication step. Proteins are usually exposed to cavitation,heat, organic solvent, or shear during the microencapsulation process. In particular,the rst emulsication step is considered as the main cause for protein denaturationand aggregation (24,39,40). Furthermore, a part of the protein strongly bound to thepolymeric matrix was found by Boury et al. (41). Due to the protein denaturation atthe water/organic solvent interface, alternative encapsulation procedures such as theanhydrous system in which the protein is dispersed (solid-in-oil-in-oil) have gainedBiodegradable Microspheres 3much attention (40,42). However, in these procedures, it is technically complex toensure the homogeneous distribution of protein powder particles in the micro-spheres. Furthermore, in many protocols, protein powder particles have to be micro-nized prior to encapsulation, which can unfold the protein. Because many of theseproblems are avoided in W/O/W encapsulation procedures, developments ofrational strategies to stabilize proteins upon W/O/W encapsulation are in progress.Several excipients such as dithiothreitol sodium dodecyl, polysaccharides such asdextran or heparin, trehalose, poloxamer 407, cyclodextrin, or bovine serum albumin(BSA) can increase protein stability (28,39,4345). Polyethylene glycol (PEG) 400added to the internal aqueous phase of the double emulsion prevented proteinadsorption at the W/O interfaces, which avoided protein denaturation during theemulsication step and reduced protein anchorage in the PLGA layer during themicroparticle preparation step (46).Very high encapsulation yields for hydrophilic molecules such as proteins areobtained by using the W/O/W double-emulsion method (47). However, it requiresmany steps, and a strict control of the temperature and viscosity of the inner W/Oemul-sion, and does not allow large quantities of hydrophilic drugs to be encapsulated (48).Another type of multiple emulsion (W/O/O/O) was developed by Iwataand McGinity (49) to produce multiphase microspheres. An internal aqueous phasecontaining a hydrophilic drug and a surfactant was emulsied in soybean oil. Thisrst emulsion was then dispersed in acetonitrile containing the polymers to form aW/O/O emulsion. Finally, the W/O/O emulsion was dispersed into a mineral-oilsolution, acting as a hardener and containing tensioactive molecules.The oil in the primary emulsion prevents contact between the internalizedhydrophilic drug (protein) and the polymersolvent system. The isolation of the pro-tein from the polymersolvent mixture prevents a possible unfolding of the proteinby the polymer or the solvent. Moreover, the possibility of polymer degradation dueto reactive proteins or drug compounds is also limited.ODonnell et al. (50) prepared multiphase microspheres of PLGA by followingthe same process but using a potentiometric dispersion technique in the last step.This technique of dispersion produces narrower dispersion and a better loading ef-ciency than the classical agitation method. ODonnell and McGinity (51) producedPLGA microspheres containing thioridazine HCl through four types of emulsions:O/W, O/O, W/O/W, and W/O/O/O. They found some degradation of PLGAmicrospheres when produced using the O/W emulsion due to a hydrolysis catalyzedby thioridazine HCl. Microspheres produced using the W/O/O/O type did notexhibit a burst effect as compared to the other types.Residual SolventsSolvents commonly used in microencapsulation via the emulsion solvent removalmethod, particularly when using chlorinated solvents such as DCM or chloroform,may be retained in the microspheres as a residual impurity, sometimes at valuesabove those authorized by the Pharmacopeia. These solvents are highly toxic andvolatile, which can induce problems in large-scale manipulation. Furthermore, ithas also been reported that an antigen becomes less immunogenic after contact withan organic solvent (52). Therefore, routine usage of these solvents is becoming com-plicated and an alternative is needed.One of the major advances in this direction is the replacement of more toxic,chlorinated solvents by less toxic solvents such as ethyl acetate, a mixture of ethyl4 Tewes et al.acetate/acetone, or ethyl formate (44,5361). Lagarce et al. (54) successfully pre-pared oxaliplatin-loaded PLGA microspheres with ethyl acetate by using the O/Wemulsicationsolvent extraction process. The encapsulation efciency was around90% and the release prole could be managed by changing the nature of the PLGApolymer.The relatively high solubility of ethyl acetate in water allows a fast diffusion ofethyl acetate from droplets into the outer aqueous phase during the O/W emulsica-tion step, which can lead to polymer precipitation rather than to the formation ofmicroparticles (53). On the other hand, as proposed by Kim et al. (62), one can slowdown the diffusion rate by saturating the outer aqueous phase with ethyl acetateprior to emulsication. A control of the ethyl acetate diffusion rate was also per-formed by Sah (53), by managing the volume of the outer aqueous phase and soli-difying the native microparticles step by step, by adding a small amount of waterin series, and by slowly extracting ethyl acetate. This allowed the production of eitherhollow or matrix-type microspheres, with different size distributions. Meng et al. (56)applied the same procedure on a W/O/W emulsion for encapsulating proteins. Theyobtained a high level of protein entrapment (always above 94%) and the full pre-servation of the entrapped lysozyme bioactivity. The release was slow, without anyburst effect. Furthermore, compared to the more hydrophobic DCM, ethyl acetatecan have a low unfolding effect on the entrapped proteins in microspheres producedby the W/O/W emulsication process (24,44).However, most researchers in this eld still choose DCM as the organic solventbecause of its physical properties such as its ability to dissolve large amounts of bio-degradable polymers, its low solubility in water (2.0%, w/v), and its low boilingpoint (39.8

C), which is compatible with the evaporation step (6367). Moreover,replacement of the DCM with ethyl acetate can reduce encapsulation efciency (17).Organic Phase Separation (Coacervation)The phase separation process has allowed the production of the rst microspheresencapsulating a peptide (nafarelin acetate) for a parenteral application at an indus-trial scale (68).This process consists in decreasing the solubility of the encapsulating polymers(PLGA, PLGA-PEG, and PLA) solubilized in an organic solvent (DCM, ethyl acet-ate, chloroform, toluene) by varying the temperature, or by adding a third compo-nent that interacts with the organic solvent but not with the polymer [coacervatingagent (CA)] (6976,48). Classes of CA can be distinguished into: (i) nonsolvents ofthe polymer, that induce coacervation by extracting the polymer solvent, and (ii)polymers that are incompatible (nonmiscible) with the wall polymers.For a particular area of the (solventpolymerCA) ternary phase diagram(Fig. 1), i.e., stability window, two liquid phases have been obtained (phaseseparation): a rich polymer phase called coacervate droplet and a phase depletedin polymers (69,70). The drug that is dispersed or sometimes dissolved in the polymersolution is coated or entrapped by the droplet of coacervate. Then, the coacervatedroplets are solidied by using a hardening agent such as heptane to produce micro-particles (microcapsules or microspheres), which are collected by washing, sieving,ltration, or centrifugation, and are nally dried (69,70,72,77). The hardening agentshould be relatively volatile and should easily remove the viscous CA on washing.This process is suitable to encapsulate both hydrophilic and hydrophobicdrugs. Hydrophilic drugs such as peptides and proteins can be dissolved in waterBiodegradable Microspheres 5and dispersed in the polymer solution to form a W/O emulsion, or directly dispersedin the organic phase (71,7476). Hydrophobic drugs are usually dispersed or some-times solubilized in the polymer solution.The CA affects both phase separation and the solidication stages of the coa-cervation process. The CA should dissolve neither the polymer nor the drug andshould be soluble in the solvent. It is added to the stirred polymerdrugsolvent sys-tem and gradually induces coacervation. The size of the resulting coacervate dropletsis controlled by the stirring rate and by the rate of addition of the CA. The stabilitywindow determines the optimum volume of CA that is added to the polymerdrugsolvent system to obtain stable coacervate droplets. The process conditions, like vis-cosity of the CA and type of polymer coating or polymer concentration, that allowthe obtaining of the stability window can be varied to obtain microparticles. Forlow CA volumes (windows 1 and 2 in Fig. 1), coacervation is not effective and stablecoacervate droplets cannot be obtained. For high CA volumes (window 4 in Fig. 1),extensive aggregation and precipitation of coacervate droplets occur.Typical CAs used with poly(a-hydroxyacid)s are low (Mw) silicone oil (poly(dimethylsiloxane)) (71,72,74,76,78), triglycerides, mineral oil, low (Mw) liquid poly-butadiene, hexane and low (Mw) liquid methacrylic polymers. Hardening agentsinclude aliphatic hydrocarbons such as hexane, heptane, octamethylcyclotetra-siloxane (OMCTS), and petroleum ether (71,72,74,76,7982).Temperature parameters, polymer concentrations, and (Mw) must be carefullyadjusted to obtain physically stabilized droplets made of poly(a-hydroxy acid)s-richphase surrounded by the poly(a-hydroxyacid)-poor phase. Thus, interfacial proper-ties and viscosity will play key roles. Moreover, the entrapment of dissolved/dispersed drugs in the coacervate phase must be carried out with conditions thatdo not affect the activity of the compound.In a sophisticated process, poly(lactide) (PLA) solution was injected intomineral oil, whereby particles of any desirable size were produced by varying thediameter of the injection equipment (80). Other modications of the classical coacer-vation procedure were made for encapsulation of nafarelin acetate (79). Thesestudies combined a phase-separation followed by a solvent-evaporation step toobtain freely owing powders.Figure 1 Ternary phase diagram of coacervation. (1) Emulsication of the CAsolventphase in polymersolvent phase, (2) beginning of a coacervation, but droplets of coacervateare unstable, (3) stability window, (4) massive aggregation and precipitation of the coacer-vate droplets. Source: From Ref. 70. Abbreviations: CA, coacervating agent; PLGA, poly(D,L-lactide-co-glycolide).6 Tewes et al.In the coacervation process, phase equilibrium is never reached. Therefore, theformulation and process variables signicantly affect the kinetics of the entire pro-cess and ultimately the characteristics of the microspheres. Moreover, the coacervatedroplets are extremely sticky and adhere to each other before completion of thephase separation operation or before hardening. Consequently, this technique tendsto produce agglomerated particles. However, adjusting the stirring rate, temperature,or the addition of a stabilizer is known to rectify this problem (71).Compared to the solvent evaporationextraction method, the choice of sol-vents is less stringent because the solvent does not need to be immiscible with waterand its boiling point can be higher than that of water. However, the method alsorequires large quantities of organic components (initial solvent and hardeningagent), which are often difcult to remove from the nal microspheres (77).In an attempt to minimize the amount of residual solvents, a low ratio of sol-vent/CA [Polydimethylsiloxane (PDMS)] was claimed to be a key parameter in con-trolling the amount of the residual hardening agent heptane in histreline-loadedPLGA microspheres (83). The suitability of volatile siloxanes such as OMCTS orhexadimethylsiloxane, as hardening agents was shown in the encapsulation of thepeptide drug triptorelin (84). The residual amount of siloxane in the nal productwas 2% to 5%. As shown by Thomasin et al. (85), the residual amounts of DCMand OMCTS depend greatly on the amount of PDMS used for coacervation.Spray DryingThe principle of spray drying by nebulization is based on the atomization of a solu-tion, containing drugs and carrier molecules, by using compressed air or compressednitrogen through a desiccating chamber, and using a current of warm air for the dry-ing process. This is performed in three steps: (i) formation of the aerosol, (ii) contactof the aerosol with the warm air and drying of the aerosol, and (iii) separation of thedried product and the air charged with the solvent.This process has been applied to the creation of microparticles by sprayingcomplex liquid mixtures containing an active principle that is dissolved/dispersedin an organic or aqueous polymer solution. The production of microspheres ormicrocapsules by spray drying depends on whether the initial formulation waswhether in the form of a solution, suspension, or emulsion. It has been used success-fully with several biodegradable polymers such as PLA, PLGA, poly(e-caprolactone)(PCL), commercial Eudragit(Degussa AG, Weiterstadt, Germany), gelatin, andpolysaccharides or related biopolymers (8698).The rst commercialized injectable microspheres, which encapsulated bromo-criptine (ParlodelLAR; Sandoz, Switzerland), were produced by spray drying. Theformulation included PLGA branched to D-glucose (91). Other research describedthis process for the encapsulation of several hydrophilic or lipophilic drugs(86,99,100). In some cases, due to the incompatibility of the hydrophilic drug tothe PLA, needle-shaped crystals of drug grew on the microsphere surface, whereasthe lipophilic drugPLA system provided smooth particles (86).Spray drying usually leads to a broad distribution of particle size, with a Gaussianshape, centered on 10mm. Flow rate, nozzle geometry, and solution viscosity are themost inuencing parameters (1).There may be a signicant loss of the product during spray drying, due toadhesion of the microparticles to the inner wall of the spray-drier apparatus, or toagglomeration of the microparticles (101). To solve these problems, a novel techniqueBiodegradable Microspheres 7has been developed; using two injection devices and mannitol as an antiadherent.Apolymerdrug solution was sprayed through one nozzle and simultaneously an aqu-eous mannitol solution was sprayed through the second nozzle. The resulting micro-spheres exhibited surfaces coated with mannitol that decreased agglomeration (101).This method produced microspheres with higher yield and encapsulation ratio whencompared to those prepared from a W/O/W emulsionsolvent removal method.The use of a novel low-temperature spraying method has been reported by thecompany Alkermes(ProLeasetechnology) for preparing PLA and DL-PLGAmicrospheres (102,103). A powder composed of protein (human growth hormone)and stabilizing excipients was suspended in a solution of polymer in acetone, ethylacetate, or DCM. This suspension was then sprayed into a vessel containing liquidnitrogen. The liquid nitrogen was then evaporated and the organic solvent of thefrozen droplets was extracted by liquid ethanol. Microspheres were then lteredand vacuum dried to eliminate residual solvents. The microspheres were 50 to60 mm in size with drug encapsulation efciency higher than 95% (102,104,105).Contrary to coacervation and emulsication methods, the spray drying methodis a one-step quick process, and is continuous, easy to scale-up, and inexpensive. It isless dependent on the solubility parameters of the drug and the polymer, and can beused without organic solvents. When used with organic solvents, the amount of resi-dual solvent in particles is often lower than that reached with emulsicationsolventremoval techniques (0.050.2%). They can, however, be higher than the limit value ofthe Pharmacopeia (0.06% for DCM). Nevertheless, a solvent less toxic than DCM,such as ethyl formate, has been widely used (88).It should be mentioned that the formation of bers instead of microspherescould occur when the sprayed solution is not sufciently broken up (86). This occurswhen the viscosity of the solution is too high (high polymer concentration, ramiedpolymers, etc.), and also when the geometry of the nozzle is not suitable, or when theow rate is too low (1). In addition, the temperature necessary to dry particles is over100

C when starting from aqueous solution, and can denature thermally labile drugssuch as proteins.TECHNIQUES WITHOUT ORGANIC SOLVENTSResidual Solvent ConsiderationsMicroparticles used as sustained-release dosage forms are mainly composed of bio-degradable polymers. Unfortunately, the applied polyesters such as PLA, PLGA,and PCL, are only soluble in toxic organic solvents such as DCM, chloroform, orto a lesser degree, ethyl acetate or ethyl formate, that are commonly used to dissolvethe coating polymer prior to microencapsulation.Classical techniques such as emulsicationsolvent removal, spray drying, andorganic phase separation, involve an extensive use of organic solvents. This aspectleads to environmental problems of pollution, toxicity due to incomplete solventremoval, and solvent impurities that may cause chemical degradation of the bioac-tive substances within the polymer matrix. It also complicates the process andincreases the cost of production.Bitz and Doelker (106) compared the residual solvent traces (commonly knownas organic volatile impurities or OVIs) in different formulations containing tetra-cosactide as a model drug. The residual amounts of solvent varied from 934 to5998 ppm for chloroform, and from 281 to 705 ppm for DCM. Vacuum drying over8 Tewes et al.three days decreased the concentration of DCM from 2 to 17 ppm. Spenlehauer et al.(107) found 30,000 ppm residuals of DCM in cisplatin-loaded microparticles manu-factured by the emulsication/solvent evaporation technique. In a previous study,Spenlehauer et al. (108) showed dependence between the residual DCM contentin microparticles and the drug content, the particle size, and the addition ofa nonsolvent to the polymer solution.Benoit et al. measured residual DCM content in progesterone-loaded micro-particles prepared by the emulsication/solvent evaporation technique. Theyshowed that vacuum drying led to a reduction of the solvent content from 18,000 to360 ppm for PLA microparticles (109) and from 47,000 to 6800 ppm for polystyreneones (110).Owing to the toxicity of the generally employed solvents, the authorities[Pharmacopeia of the United States (USP), Europe (PhEur), and Japan (JP)] imposelimitations in pharmaceuticals. Since 1997, the limited values imposed by the threePharmacopeia are going to be harmonized by the International Conference onHarmonization (ICH), but only the PhEur and the JP have fully adopted the ICHguidelines (111).The maximum limits for chloroform and DCM (which belong to Class 2 sol-vents a