drug photostability: the science and application of photo ...indoor lighting direct sunlight....
TRANSCRIPT
Drug Photostability: The Science and
Application of Photo-Produced
Reactive Oxygen Species
Steven W. Baertschi, Ph.D.
Baertschi Consulting, LLC
Email: [email protected]
Website: http://baertschiconsulting.com
October 14-15
Science of Stability Conference
Amsterdam, Netherlands
Introduction
Photostability of Drugs: Background
Photochemistry Basics
– Terminology, Definitions, Light sources and measurements, Jablonski Diagram, etc.
Photosafety Context
Direct and Indirect Photochemistry
Methods for Measurement of ROS
Conclusions / Summary
Drug stability and the environment
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http://www.hazemsakeek.com/QandA/Phloresent.htm
Direct
Sunlight
Window-filtered
Sunlight
Light and the hospital environment
http://www.onmeda.de/arztbesuch/behandlung/chemotherapie.html
http://www.bannerhealth.com/resources/infusion-225px.jpg
http://www.apollolighting.co.uk/articles/partnership.php
Through a windowLight/radiation below 310
nm cannot penetrate a
window pane
Indoor lighting Direct
Sunlight
Photostability Issues in Marketed Products
Overall impact of photostability is evident from an examination of the USP 27 (2004) Reference Table “Containers for Dispensing Capsules and Tablets”– 743 pharmaceutical products listed
– 248 (33%) require light resistant packaging
Developing an improved understanding is desirable– To effectively control the quality of the product
– Address the specific requirements of each product
Presented by Robert A. Reed, AAPS Workshop on Stress Testing and
Degradation Chemistry, Nov 10, 2007, San Diego, CA
The Spectrum of Electromagnetic Radiation
Lehninger, Principles of
Biochemistry, 3rd ed., p. 693.
UV-Vis Wavelength Ranges
UV-C: <290 nm (<280 nm, CIE)
UV-B: 290-320 nm (280- 315 nm, CIE)
UV-A: 320-400 nm (315-400, CIE)
Visible: 400-800 nm
First Law of Photochemistry:Grotthuss (1817) – Draper (1843)
“Only radiation that is absorbed by a system
can be effective in producing a photochemical
reaction.”
The “system” is not just the API.
For a formulation, one must consider all
components in the formulation
Photochemistry Basics
The interaction of matter
with electromagnetic radiation
So(singlet ground
state – almost all
organic molecules)
hn(absorption)
S1(First excited
singlet state)T1(First excited
triplet state)
Energy
hn’(fluorescence)
hn’(phosphorescence)
Vibrational
relaxationMultiplicity = 2s+1, where s=(±½)
ISC
Light Absorption by a Molecule –What can a molecule do with the energy?
The Jablonski Diagram
The molecule will typically get rid of the excess energy
based on a combination of kinetic/thermodynamic factors
slide provided courtesy of Mark Kleinmann, GSK, USA
heat
(internal conversion)
heat
(internal
conversion)
(Inter-System
Crossing)
10
Measuring Light: Radiometric vs
Photometric Units
Courtesy of Allen Zielnik, Atlas Material Testing Technology, LLC.
Mixing Terminology
ICH Terminology for light measurements
For confirmatory studies samples should be exposed to [Visible] light providing an overall illumination of not less than 1.2 million Lux-hours
and
an integrated near-ultraviolet energy of 200 watt-
hours/square-meter to allow direct comparisons to be
made between the drug substance (API) and the drug
product (FPP).
A confusing issue with the Guideline is that it mixes radiometric
and photometric light measurements . . .
Rational for Confirmatory Photostability
Exposure Recommended by ICH
•3 months of continuous exposure to visible light without protective packaging in the pharmacy, warehouse, or home. (~400 – 800 nm, 500 lux x 24 h x 100 days = 1.2 x 106 lux•hrs, visible radiation).
•Over the same 3 months, the product could be exposed to solar radiation behind windowed glass, which was [somewhat arbitrarily] defined as 200 watt•hrs/m2 of integrated near UV radiation (~300 -400 nm). This is roughly equivalent to 1-2 days of “windowsill” exposure.
Thatcher, S.R.,* Mansfield, R.K., Miller, R.B., Davis, C.W., and Baertschi, S.W.* “Pharmaceutical Photostability: A Technical and Practical Interpretation of the ICH Guideline and Its Application to
Pharmaceutical Stability: Part I”, Pharmaceutical Technology, 25:3, pp. 98-110, March (2001).
ICH Q1B Confirmatory
Exposure in Perspective
UV (295-400 nm)
• The average daily UV irradiance is:
– 358 W-h/m2 in Miami, FL, USA
– 154 W-h/m2 in Oslo, Norway
• VISIBLE (400-800 nm)
14
--from Baertschi, SW et al., J.
Pharm. Sci. (2013) ); 102:11,
3888-3899.
--from Baertschi, SW et al., J.
Pharm. Sci. (2013) ); 102:11,
3888-3899.
For Reference…
Sun intensity in Miami on a clear summer day…
• from the Eppley total UV radiometer in Miami,* (July 24, 1996)
– the “total” UV dose for the day
– 473 W-h/m2 (295-400 nm)
– the “total” UV dose between 10 am and 2 pm...
– 245 W-h/m2 (295-400 nm)
*Courtesy of Norma Searle, Ph.D., consultant, and
Atlas Electric Devices, Chicago, IL
Measuring Light: Photometry
The photometric system (e.g., lux) defines light in terms of how it is perceived by the human eye
Slide courtesy of Allen Zielnik, Atlas Material Testing Technology, LLC.
(Night Vision)
(Day Vision)
Lux-hours
Lux X time (hours) = Exposure in Lux-Hours
1 lux = 0.0929 ft-candles
1 ft-candle = 10.76 lux
1 ft-candle = 1 lumen/ft2
meter candle = 1 lux = 1 lumen/m2
The
Human
Eye
Direct: Drug molecules absorb UV or visible radiation resulting in
transformation into a photoproduct
Indirect (sensitized): The primary excited species mediates the
formation of secondary reactive species which subsequently lead to
the formation of the photoproduct .
Direct and Indirect Photoreactivity
Drughn
Drug*
Photoproduct(s)
Direct: Drug molecules absorb UV or visible radiation resulting in transformation into a photoproduct
Indirect (sensitized): The primary excited species mediates the formation of secondary reactive species which subsequently lead to
the formation of the photoproduct .
– Type I(simplified view)
– Type II
Direct and Indirect Photoreactivity
Drug
hn
Drug* 3O2
Drug Reactive oxygen species+
HOO , O2 , HO(or othercomponent)
(or othercomponent)
Drug
Photoproduct(s)
Groundstate
Excitedstate
Radical orrelated species
(or othercomponent)
Drug
hn
Drug* 3O2
(or othercomponent)
(or othercomponent)
Drug +
(or othercomponent)
1O2
singlet oxygen
Drug
Photoproduct(s)
Potential
Photosafety
Concerns
Summary of Potential
Photochemical Processes
Direct
Indirect
Indirect
Potential
Photosafety
Concerns
Photosafety
➢ ICH S10 Photosafety Evaluation of
Pharmaceuticals
➢Applies to new APIs, new excipients, new
dermal application formulations,
photodynamic therapy products
➢Depends on:
➢Photochemical properties (UV-VIS absorption,
photostability, and ROS production)
➢Phototoxic potential of related compounds
➢Tissue Distribution
➢Clinical / non-clinical findings indicative of
phototoxicology
Prediction of Potential Phototoxicity
using Chemistry
Interrogate:
– UV-VIS absorption in 290-800 nm region
(MEC >1000 M-1cm-1 )
– Photoexposure of API in solution (to simulated
sunlight) for a total exposure in the UV region
of 5 J/cm2 = ~14 W-h/m2 (290-400 nm)
➢Measure total photodegradation
➢Measure formation of superoxide radical anion
(Type I)
➢Measure formation of singlet oxygen (Type II)
Experimental Filters for In-Vitro
Phototoxicity Predictions
Chemistry of Reactive Oxygen
Species: Hydroperoxyl Radical
HOO • + R-H HOOH + R •
H-atom transfer reaction
Exothermic by 5 to 20 kcal/molReaction occurs at the rate of diffusion
+ O2 OO
tBu radical tBu peroxyl radical
HOO-H R-H
Bond Dissociation Enthalpies (BDEs) as a Guide to Free Radical Reactivity
BDE ~88 kcal/mol BDE ~variable with structure, 70-105 kcal/mol
If R-H BDE is less than 88 kcal/mol, H-atom transferreaction will likely occur.
Chemistry of Reactive Oxygen
Species: Superoxide
The Chemistry of Superoxide radical ion
1. dismutes rapidly in water
2 O2 + 2H+H2O2 + O2
O2 + H+ HOO •, a reactive species2. forms a neutral free radical
3. In organic solvents (DMSO) is stable and a modest nucleophile
O2 + R-X ROO • + X
p
pp
p* p*p
pp
p* p*
p
pp
p* p*
Ground State Oxygen, 3O2
Singlet Oxygen 1st Excited State, 1O2
22.5 kcal/mole higherenergy than ground state
1-g
1g
3+g
37.8 kcal/mole higherenergy than ground state
Singlet Oxygen 2nd Excited State, 1O2
Chemistry of Reactive Oxygen
Species: Singlet Oxygen
1O2
Measuring Singlet Oxygen and
Reactive Oxygen Species
Article describes relatively simple methodology
involving
(1) bleaching of a singlet oxygen acceptor (imidazole) monitoring
440 nm absorbance
(2) the reduction of nitroblue tetrazolium (increase in absorbance
at 560 nm) by superoxide
Measurement of Singlet Oxygen Formation Using
Method of Kraljic and Mohsni
Measurement of Superoxide Radical Anion by
Reduction of Nitroblue Tetrazolium
Reduction of NBT via a
one-electron reduction
(from superoxide radical
anion) forms
monoformazan, which
can be quantitatively
determined by the
absorbance at 560 nm.
Correlation of ROS Production with
Known Phototoxicity
Plot of photo-induced
singlet oxygen and
superoxide generation
for 39 compounds.
Open circles represent
non-phototoxic
compounds
Photochemistry and Photostability:
Useful References
A. Albini and E. Fasini, Editors, “Drugs: Photochemistry and Photostability”, (1998), The Royal Society of Chemistry.
Gilbert and J. Baggott, “Essentials of Molecular Photochemistry - Photostabilityof Drugs and Formulations” (1991) CRC Press.
H.H. Tønneson, Editor, “Photostability of Drugs and Drug Formulations”, 1st
Edition (1996), Taylor & Francis, 2nd Edition (2004) CRC Press
Baertschi / Alsante / Reed, Eds. “Pharmaceutical Stress Testing” (2011) CRC Press.
J.T. Piechocki and K. Thoma, Editors, “Pharmaceutical Photostability and Stabilization Technology”, (2007) Informa Healthcare.
N. J. Turro, V. Ramamurthy, J. C. Scaiano, “Modern Molecular Photochemistry of Organic Molecules, University Science Books, (2010).
Thatcher, S.R., Mansfield, R.K., Miller, R.B., Davis, C.W., and Baertschi, S.W. “Pharmaceutical Photostability: A Technical and Practical Interpretation of the ICH Guideline and Its Application to Pharmaceutical Stability: Parts I and II”, Pharmaceutical Technology, 25:3&4, March-April (2001)
CRC Handbook of Organic Photochemistry and Photobiology, 2nd
Ed, Horspool, Lenci, Editors, CRC Press (2004)
Templeton AC, Xu H, Placek J, Reed RA, “Implications of
Photostability on the Manufacturing, Packaging, Storage, and
Testing of Formulated Pharmaceutical Products”, Pharm Technol,
29:3 (2005) 68-83.
Photobiological Sciences Online
– Excellent online resource for many topics related to photostability,
photochemistry, photobiology, etc.
– http://www.photobiology.info/
B.A. Kerwin, R.L.J. Remmele, “Protect from light:
Photodegradation and protein biologics”, J Pharm Sci 96 (2007)
1468–1479, http://dx.doi.org/10.1002/jps.20815.
32
Photochemistry and Photostability:
Useful References
Summary / Conclusions
➢ Many drugs are associated with photostability issues
➢ A subset of these are associated with photosafety concerns
➢ Photosafety issues are strongly correlated with Type I
(superoxide production) and Type II (singlet oxygen
production) photodegradation processes
➢ Singlet oxygen and superoxide radical anion production
can be readily measured using established procedures
➢ Simulated sunlight exposure, 14 W-h/m2 (290-400 nm) (7% of the
ICH Q1B 200 W-h/m2 confirmatory exposure)
➢1O2 measured by RNO bleaching in presence of imidazole
(decreased absorbance at 440 nm)
➢ Superoxide radical anion measured by 1-electron reduction of
NBT (increased absorbance at 560 nm)
Acknowledgements
FreeThink Technologies, Inc. for hosting
the conference and for the opportunity to
give this presentation!