bioavailability of nerodilol-based transdermal therapeutic system of nicorandil in human volunteers

www.elsevier.com/locate/jconrel

Journal of Controlled Releas

Bioavailability of nerodilol-based transdermal therapeutic system

of nicorandil in human volunteers

Y.S.R. Krishnaiah a,*, S.M. Al-Saidan a, D.V. Chandrasekhar b, V. Satyanarayana c

aDepartment of Pharmaceutics, Faculty of Pharmacy, Kuwait University, PO Box 24923, Safat 13110, KuwaitbDepartment of Pharmaceutical Sciences, Andhra University, Visakhapatnam-530 003, IndiacSipra Labs Pvt. Ltd., 407, Nilgiri, Aditya Enclave, Ameerpet, Hyderabad-500 038, India

Received 29 September 2004; accepted 25 April 2005

Available online 1 July 2005

Abstract

The objective of the present investigation was to design and evaluate a nerodilol-based transdermal therapeutic system (TTS)

for finding its ability in providing the desired steady-state plasma concentration of nicorandil in human volunteers. The

influence of EVA2825 membrane, adhesive-coated EVA2825 membrane and adhesive-coated EVA2825-rat skin composite on

the in vitro permeation of nicorandil from a nerodilol-based HPMC gel drug reservoir was studied against a control (excised rat

skin alone). The flux of nicorandil from the nerodilol-based HMPC drug reservoir across excised rat skin (control) was

384.0F4.6 Ag/cm2 h and this decreased to 222.7F7.1 Ag/cm2 h when studied across EVA2825 membrane indicating that

EVA2825 membrane was effective as rate controlling membrane. The flux of the drug decreased to 183.8F5.7 Ag/cm2 h on

application of a water-based acrylic adhesive (TACKWHITE A 4MEDR) coat to EVA2825 membrane. However, the flux of

nicorandil across adhesive-coated EVA2825-membrane–rat-skin composite was 164.8F1.8 Ag/cm2 h, which was 1.74-times of

the required flux that prompted for preparation of TTS. The nerodilol-based drug reservoir system was sandwiched between a

composite of adhesive-coated EVA2825 membrane-release liner and a backing membrane. The resultant sandwich was heat-

sealed to produce circle-shaped TTS (20 cm2) that were subjected to bioavailability study in human volunteers against

immediate release nicorandil tablet. The nerodilol-based TTS provided a steady-state plasma concentration of 25.5 ng/ml for

24 h in human volunteers. It was concluded that the nerodilol-based TTS of nicorandil provided the desired plasma

concentration of the drug for the predetermined period of time with minimal fluctuations.

D 2005 Published by Elsevier B.V.

Keywords: Bioavailability; Preparation; Nerodilol; Nicorandil; TTS; Human volunteers

0168-3659/$ - see front matter D 2005 Published by Elsevier B.V.

doi:10.1016/j.jconrel.2005.04.021

* Corresponding author. Tel.: +965 4986034; fax: +965 5342807.

E-mail address: [email protected] (Y.S.R. Krishnaiah).

1. Introduction

Scientists from various disciplines are bringing

exciting developments in the field of enhanced skin

permeability in the last decade. In spite of this excel-

e 106 (2005) 111–122

Y.S.R. Krishnaiah et al. / Journal of Controlled Release 106 (2005) 111–122112

lent achievement, transdermal patches exist only for a

few drugs such as scopolamine, nitroglycerin, nico-

tine, clonidine, fentanyl, estradiol, testosterone, and

oxybutinin [1]. This reflects the inability to deliver

sufficient quantities of therapeutic agents across the

skin to maintain the desired plasma concentration. The

stratum corneum is the commonly accepted barrier to

transdermal permeation of drugs across the skin [2].

Overcoming this barrier safely and reversibly is a

fundamental problem that persists in the field of trans-

dermal delivery. The skin is composed of dead, flat-

tened cells filled with keratin in the form of regular

array of protein-rich cells embedded in an intercellular

and multicellular lipid domain running parallel to the

skin [3]. Barrier properties of the stratum corneum

may be manipulated by using several techniques. The

most promising technique is the use of penetration

enhancers that allow drug permeation through the skin

at an appropriate rate for a suitable time. Willams and

Barry (2004) have reviewed the use of penetration

enhancers for use in transdermal drug delivery sys-

tems [4]. The various chemical penetration enhancers

that have been studied are azone and its analogues,

pyrrolidones, polyunsaturated fatty acids, alkanols,

polymeric enhancers, non-ionic surfactants and ter-

penes [5–13]. The safety of chemical penetration

enhancers is of primary consideration while selecting

them for use in the development of membrane-mod-

erated transdermal therapeutic systems (TTS). Ter-

penes are of low cutaneous irritancy, generally

regarded as safe, provide excellent enhancement abil-

ity and, thus appear to be promising candidates for

transdermal formulations [4,14]. A variety of terpenes

has been shown to increase the percutaneous absorp-

tion of both hydrophilic and lipophilic drugs [15–17],

and hence could be used as penetration enhancers for

increasing the permeation of a lipophilic drug such as

nicorandil from a transdermal therapeutic system.

Nicorandil, a potassium channel activator charac-

terized by its arterial vasodilator properties, is used in

the treatment of angina pectoris [18,19]. It is subjected

to hepatic first-pass metabolism following oral admin-

istration with systemic bioavailability of about 75%

[20]. Because of its short elimination half-life (1 h),

the drug has to be given frequently at 10 to 20 mg

twice daily [18]. Thus, the conventional therapy may

result in higher fluctuation in plasma concentration of

the drug resulting in unwanted side effects. Hence, the

development of a TTS for nicorandil that could pro-

vide the desired constant drug delivery for a prede-

termined period is beneficial for an effective and safe

therapy of angina pectoris.

The various approaches for achieving transdermal

drug delivery are reservoir-type membrane-moderated

systems, adhesive diffusion-controlled systems, ma-

trix diffusion-controlled systems and microreservoir

systems. Of these, reservoir-type membrane-moderat-

ed TTS are considered advantageous in providing

desired plasma concentration of the drug for the pre-

determined time with minimal fluctuations. Thus, the

broad objective of the present study was to design a

membrane-moderated TTS of nicorandil. In this con-

text, it was reported that nicorandil is a potential drug

candidate for formulation as TTS after predicting its

permeation across human skin based on its in vitro

permeation through animal skin model [21,22]. In

addition to these preliminary reports, only one report

existed in the literature on the development of mono-

lithic TTS for nicorandil [23]. Based on this informa-

tion, studies were carried out with a broad objective of

developing membrane-moderated TTS using terpenes

as penetration enhancers. It was reported that hydro-

xypropyl methylcellulose (HPMC) gel drug reservoir

system prepared with 70% v/v ethanol-water solvent

system containing 6% w/w of limonene was effective

in promoting the in vitro transdermal delivery of

nicorandil across excised rat skin [24]. In the light

of this observation, further study was carried out to

investigate the penetration enhancing effect of two

more terpenes, nerodilol and carvone on the in vitro

transdermal permeation of nicorandil from HPMC gel

formulations [25]. Such a comparative study is useful

in choosing the right transdermal formulation among

the three terpene-containing HPMC gel drug reser-

voirs with respect to their ability in providing con-

trolled in vivo drug release in humans with minimal or

no adverse effects on skin.

The flux of nicorandil across excised rat skin was

384.0F4.6 Ag/cm2 h from the HPMC gel reservoir

system with 10% w/w of nerodilol, which was about 4

times the required flux for producing the desired

plasma concentration for the predetermined period in

humans. The required flux of nicorandil so as to

provide a steady-state plasma concentration (Css) of

15 ng/mL was calculated by using the equation: Re-

quired flux=Css�Vd�ke /Area of TTS, where Css is

Y.S.R. Krishnaiah et al. / Journal of Controlled Release 106 (2005) 111–122 113

the desired steady-state concentration, Vd is volume of

distribution and ke is the elimination rate constant.

The mean values of pharmacokinetic parameters of

nicorandil, as reported by Frydman [20], were substi-

tuted in the above equation to calculate the required

flux (Css=15 ng/mL, Vd=60,000 mL, ke=0.693 h-1

and area of the TTS patch=6.6 cm2), and thus the

required flux of nicorandil was 94.7 Ag/cm2 h. In the

light of the observed percutaneous penetration en-

hancing activity of nerodilol across the excised rat

skin, further studies were carried out to prepare and

evaluate the nerodilol-based membrane-moderated

TTS for their ability in providing a steady state plasma

concentration of nicorandil for the desired time period

in humans. In the present investigation, the in vitro

permeation of nicorandil across excised rat skin,

EVA2825 membrane (ethylene vinyl acetate copoly-

mer with 28% vinyl acetate), adhesive-coated

EVA2825 membrane and adhesive-coated EVA2825-

membrane–rat-skin composite was studied from a

nerodilol-based HPMC gel drug reservoir system to

investigate their influence on the desired flux of

nicorandil. Based on these results, nerodilol-based

membrane-moderated TTS of nicorandil were pre-

pared. Further, bioavailability study was conducted

in human volunteers to find the ability of the nerodi-

lol-based TTS of nicorandil in providing the desired

plasma concentration of the drug for the pre-deter-

mined time period.

2. Materials and methods

2.1. Materials

Nicorandil and d-l-nerodilol (purity 98%) were

obtained from M/s. Aarti Drugs Ltd., Mumbai, India

and M/s. Merck-Schuchardt, Germany, respectively.

Ethylene vinyl acetate copolymer beads with 28%

vinyl acetate (EVA2825) were gift samples from M/

s. National Organic Chemical Industries Limited

(NOCIL), Mumbai, India. The water-based pressure-

sensitive acrylic adhesive emulsion (TACKWHITE A

4MEDR) was a gift sample from M/s. Ichemco, Italy.

Hydroxypropyl methylcellulose (HPMC, Type 2208

[K3LV]) was a gift sample from M/s. Dr. Reddy’s

Laboratories Pvt. Ltd., Hyderabad, India, and was of

USP/NF quality. Acetonitrile (HPLC grade) and water

(HPLC), ethanol (AR grade), potassium dihydrogen

orthophosphate (AR grade), ethyl acetate (AR grade),

sodium hydroxide (AR grade), ammonia (AR grade)

and glacial acetic acid (AR grade) were obtained from

M/s. Qualigens Fine Chemicals, Mumbai, India.

2.1.1. Preparation of nerodilol-based HMPC gel drug

reservoir

The HPMCwas dispersed in 70% v/v ethanol-water

to form a gel. Nicorandil (4% w/w) and nerodilol (10%

w/w) were added to HMPC gel and mixed well for

complete dissolution or dispersion. The drug reservoir

systems, so prepared, were left overnight at room

temperature (28 to 30 8C). The drug content of the

reservoir system was determined by HPLC method.

2.1.2. HPLC analysis of nicorandil

The quantitative determination of nicorandil was

performed by High Performance Liquid Chromatogra-

phy (HPLC). A gradient HPLC (Shimadzu HPLC

Class VP series) with two LC-10AT VP pumps, a

variable wave length programmable UV/VIS Detector

SPD-10A VP, a CTO-10AS VP Column oven (Shi-

madzu), an SCL-10AVP system controller (Shimadzu),

a disposable guard column LC-18 ((Pelliguardk, LC-

18, 2 cm, Supelco, Inc., Bellefonte, PA) and a RP C-

18 column (250 mm�4.6 mm I.D., particle size 5 Am;

YMC, Inc., Wilmington, NC 28403, U.S.A) was used.

The HPLC system was equipped with the software

bClass-VP series version 5.03 (Shimadzu)Q.The mobile phase consisted of acetonitrile and 0.02

M phosphate buffer. The mobile phase components

were filtered before use through 0.45-Am membrane

filter and pumped in the ratio of 38 :62 (acetonitrile:

0.02M potassium dihydrogen orthophosphate) from

the respective solvent reservoirs. The flow rate of

the mobile phase was maintained at 0.8 ml/min, and

the column temperature was maintained at 40 8C. Aseries of drug solutions with varying concentration of

nicorandil ranging from 0.2 to 20 Ag/ml were pre-

pared and injected into the HPLC column. The col-

umn pressure varied from 85 to 90 kgf/cm2. The

eluent was detected by UV detector at 254 nm, and

the data were acquired, stored and analyzed with the

software Class-VP series version 5.03 (Shimadzu). A

good linear relationship was observed between the

peak area of nicorandil and its concentration with a

high correlation coefficient (r=0.9999). The method


was found to be precise (intra- and inter-day variation

was found to be less than 2.5%) and accurate (mean

recovery 99.9%). The standard curve, constructed as

described above, was used for estimating nicorandil in

either permeate samples or nerodilol-based HPMC gel

drug reservoir.

2.1.3. Quantitative determination of nicorandil in

nerodilol-based drug reservoir

The content uniformity of nicorandil in nerodilol-

based HPMC gel drug reservoir was estimated before

fabricating the TTS. One gram of the HPMC gel

formulation was accurately weighed, placed in 100-

ml volumetric flask containing 30 ml of mobile phase,

stirred for 30 min and made up to volume. The

resultant mixture was filtered through a 0.45-Ammembrane filter and injected into the HPLC system.

The amount of nicorandil was estimated from the

standard curve as described above.

2.1.4. Preparation of EVA2825 membranes

The EVA2825 copolymer membranes (vinyl ace-

tate content 28% w/w) were prepared for their

intended use as rate controlling membranes in the

preparation of the proposed nerodilol-based mem-

brane-moderated TTS of nicorandil. The membranes

were prepared by solvent extrusion using a glass

substrate technique. bMembrane-casting apparatusQ,fabricated in our laboratory, was utilized for the prep-

aration of the membranes. Briefly, the procedure in-

volved pouring of 4% w/v polymer (EVA) solution on

to a glass frame (100 cm2) and allowing the solvent to

evaporate slowly. The thickness of the resultant mem-

brane was measured randomly at ten points using a

micrometer (M/s. Blue Steel Engineers Pvt. Ltd.,

Mumbai, India) to test uniformity in the thickness.

These membranes were evaluated for their ability to

act as a rate controlling membrane for the controlled

release of nicorandil from the nerodilol-based HPMC

gel drug reservoir system.

2.1.5. Application of an adhesive coat to EVA2825

membrane

A pressure-sensitive adhesive TACKWHITE A

4MEDR was applied uniformly over the EVA2825

membrane with the help of a glass rod, and allowed

to dry in the air at room temperature (25 8C). Thethickness of adhesive-coated EVA2825 membrane was

measured randomly at ten points using a micrometer

(M/s. Blue Steel Engineers Pvt. Ltd., Mumbai, India).

2.1.6. Preparation of excised rat skin

In the present study, excised rat skin was used as a

skin model. The rats used were male albino rats (150–

200 g) and obtained from M/s Ghosh Enterprises,

Kolkota, India. They had a free access to food and

water until used for the study. The care of the rats was

in accordance with the institutional guidelines. The

rats were euthanized using carbon dioxide asphyxia-

tion before the experiments. The dorsal hair was

removed with a clipper and full thickness skin was

surgically removed from each rat. The excised rat skin

was prepared by a heat separation technique [15]. The

entire abdominal skin was soaked in water at 60 8Cfor 60 s, followed by careful removal of the epidermis

(abdominal skin). The excised rat skin, so prepared,

was washed with water and examined for physical

damage by using magnifying lens. The epidermis that

is free from physical damage was used for in vitro

permeation studies.

2.1.7. In vitro permeation studies

Modified Keshary–Chien diffusion cells [26] were

used in the in vitro permeation studies. The excised rat

skin, EVA2825 membrane, adhesive-coated EVA2825

membrane or adhesive-coated EVA2825 membrane-

excised rat skin composite was mounted between the

two compartments of the diffusion cells. The effective

diffusion area was 6.6 cm2. The volume of receiver

compartment was 35 ml. Two grams of nerodilol-

based drug reservoir containing 80 mg of nicorandil

was added to the donor cell. The solvent system (70%

v/v ethanol-water) was added to the receiver cell. The

cells were placed on a magnetic stirrer with heater

(Remi Equipments, Mumbai, India) and temperature

maintained at 37F0.5 8C. The contents in the receivercompartment were stirred with the help of a magnetic

bar at 500 rpm. At predetermined times (1, 2, 4, 8, 12,

18 and 24 h), permeate samples (0.5 ml) were with-

drawn from the receiver compartment and replaced

with an equivalent amount of drug-free solvent (70%

v/v ethanol–water) to maintain a constant volume.

The permeate samples were assayed for nicorandil

by HPLC method. In permeation studies with the

adhesive-coated EVA2825 membrane, the coated sur-

face of the membrane was facing the receiver com-


partment. During the in vitro permeation studies with

adhesive-coated EVA2825-membrane–rat-skin com-

posite, the coated surface of EVA2825 membrane

was stuck to the stratum corneum side of rat skin

and mounted between two compartments of diffusion

cell with uncoated surface of EVA2825 membrane

facing donor compartment.

Ethanol–water solvent sytem (70 :30 v/v) was used

in receptor compartment to avoid changes in thermo-

dynamic activity of the drug in donor compartment.

The same strength of ethanol–water (70 :30 v/v) was

used in donor compartment and receiver compartment

of the diffusion cell. If it were the phosphate buffer

system used in the receiver compartment to simulate

blood, ethanol molecules might have diffused from

the donor compartment to the receiver compartment

and in turn changed the thermodynamic activity of the

drug in the donor compartment. Though phosphate

buffer system simulates blood, it cannot provide the

sink conditions with a static diffusion cell used in the

present study. Thus, ethanol–water solvent system

was used in the receiver compartment to prevent the

change in thermodynamic activity of the drug and to

provide sink conditions. Also, 70 :30 v/v ethanol–

water is effective against microbes and prevents the

possible contamination of the skin maintaining the

skin integrity during 24 h study.

The possible dehydration effect of ethanol–water

was considered while choosing it as a solvent sys-

tem. The in vitro permeation of nicorandil across

excised rat skin increased with an increase in ethanol

concentration up to 75% v/v, but decreased with

higher ethanol concentration [24]. It is possible that

higher ethanol levels caused dehydration of the bio-

logical membrane and reduced permeation of nicor-

andil across rat skin. For this reason, only 70% v/v

ethanol–water was chosen as the solvent system for

further studies in the development of membrane-

moderated TTS of nicorandil. Further, at a concen-

tration of 70% v/v it showed synergistic penetration

enhancing effect with limonene [24], carvone and

nerodilol [25] on in vitro transdermal delivery of

nicorandil.

2.1.8. Preparation of nerodilol-based TTS of

nicorandil

The nerodilol-based membrane-moderated TTS of

nicorandil was prepared by sandwiching HPMC gel

drug reservoir between a drug-impermeable backing

laminate (3Mk Scotchpakk 9732, a polyester film

laminate with ethylene vinyl acetate heat-sealable

layer) and a rate-controlling EVA2825 membrane

coated with a water-based pressure-sensitive acrylic

adhesive emulsion (TACKWHITE A 4MEDR). Thedrug reservoir system consisted of 4% w/w of nicor-

andil and a penetration enhancer (10% w/w of nero-

dilol) in 2% w/w of HPMC gel prepared with

ethanol–water (70% v/v) solvent system [25]. To

ensure intimate contact of the transdermal TTS to

the skin, a pressure-sensitive adhesive polymer emul-

sion (TACKWHITE A 4MEDR) was coated on to the

rate-controlling EVA2825 membrane and allowed to

dry completely. A release liner (3Mk Scotchpakk1022, a polyester film coated with fluoropolymer) was

pressed over the adhesive-coated surface of EVA2825

membrane. Two grams of nerodilol-based HPMC gel

drug reservoir containing 80 mg of nicorandil (4% w/

w) and 10% w/w of nerodilol was placed over the

uncoated surface of adhesive coated EVA2825 mem-

brane-release liner composite, which in turn was

placed on a slightly grooved surface, and then covered

with a backing laminate (3Mk Scotchpakk 9732, a

polyester film laminate with ethylene vinyl acetate

heat-sealable layer). The resultant sandwich was

heat-sealed to form a circle-shaped TTS (20 cm2)

with the drug reservoir in the center and trimmed.

Then, each TTS was kept in a sealed aluminum pouch

to minimize the loss of solvent (ethanol).

2.1.9. Bioavailability of nerodilol-based TTS of

nicorandil in human volunteers

The study was conducted at M/s. Sipra Labs Pvt.

Ltd., Hyderabad, India. The protocol of the study in

human volunteers was approved by the Institutional

Ethics Committee. Six healthy male volunteers (55–

60 kg, age between 25–30 years) participated in the

study, and all were nonsmokers and non-alcoholics.

The biochemical examination of the volunteers

revealed normal function of the kidney and liver.

The nature and purpose of the study were fully

explained to them. An informed written consent was

obtained from every subject. The volunteers had a

freedom to withdraw from the study at their discre-

tion. None of the volunteers were on drug treatment

one week prior to the participation of the study. The

volunteers were divided into two groups (Group I and


Group II), and a cross over study was carried out. An

immediate release tablet dosage form containing 5 mg

of nicorandil was chosen as a reference formulation,

and was administered to 3 volunteers (group I). The

volunteers (Group I) received the tablet formulation

on empty stomach with 240 ml of water. Group II

(n=3) volunteers applied nerodilol-based TTS of

nicorandil (20 cm2) to the anterior surface of the

forearm near the elbow. Standard breakfast was served

2 h post-study. After a washout period of 10 days,

Group I volunteers applied nerodilol-based TTS of

nicorandil and Group II received the reference formu-

lation (immediate tablet dosage form). The volunteers

had a freedom to remove the TTS during the study (24

h), in case of any sign of irritation at the application

site. Blood samples were collected from the volun-

teer’s cubical vein of the forearm via a hypodermic

syringe (rinsed with dilute heparin solution) over a

period of 24 h (0, 0.25, 0.5, 1, 1.5, 2, 4, 6, 8, 10, 12,

18 and 24 h). The blood samples were mixed well,

immediately centrifuged at 5000 rpm, plasma separat-

ed and stored at �40 8C until analysis by HPLC.

2.1.10. HPLC analysis of nicorandil in human plasma

The quantitative determination of nicorandil in

human plasma was performed by HPLC using the

equipment described above. An aliquot (0.5 ml) of

plasma sample was measured into a glass tube with a

teflon-lined cap, followed by the addition of 0.2 ml of

0.1M sodium hydroxide and 2 ml of ethyl acetate The

mixture was vortexed for 5 min and centrifuged for 10

min at 3000 rpm. The ethyl acetate extract (organic

layer) was transferred to glass tube with a teflon-lined

cap. The aqueous portion was extracted again with

another 2 ml of ethyl acetate and centrifuged. The

second portion of the ethyl acetate extract was added

to the first portion of ethyl acetate extract and evap-

orated to dryness under vacuum. The residue was

reconstituted with 0.2 ml of mobile phase, and 20

Al of the resultant solution was injected into reverse

phase C-18 column through which the mobile phase

components (consisted of acetonitrile and 0.03M am-

monium acetate buffer in the ratio of 26 :74) were

pumped at a flow rate of 0.8 ml/min. This yielded a

column back pressure of 85–90 kg f/cm2. The eluents

were monitored at 254 nm, the data acquired, stored

and analyzed using the software bClass-VP series

version 5.03 (Shimadzu)Q. The peak area of nicorandil

was determined, and this was used to find the plasma

concentration of nicorandil from the regression equa-

tion obtained after constructing the calibration curve.

The calibration curve was obtained by spiking drug-

free plasma with varying amounts of nicorandil (5–

200 ng/0.5ml), treating the plasma samples as de-

scribed above and estimating the peak areas. A good

linear relationship was observed between the plasma

concentration of nicorandil and the peak area of nicor-

andil with a high correlation coefficient (r=0.9995) in

the range of 10 to 200 ng/0.5 ml. However, the lower

detection limit was found to be 5 ng/0.5 ml. The

method was found to be precise (intra- and inter-day

variation was found to be less than 4%) and accurate

(mean recovery 97.6%). Whenever a lower amount of

drug less than the minimum detection limit was ob-

served, the HPLC analysis was repeated with a larger

quantity of plasma sample.

2.1.11. Data analysis

The concentration of nicorandil in permeate sam-

ples was corrected for sampling effects according to

the equation described by Hayton and Chen [27]:

C1n ¼ Cn VT=VT � VSð Þ C1

n�1=Cn�1

� �

where C1n is the corrected concentration of the nth

sample, Cn is the measured concentration of nicoran-

dil in the nth sample, Cn-1 is the measured concen-

tration of the nicorandil in the (n -1)th sample, VT is

the total volume of the receiver fluid, and VS is the

volume of the sample drawn.

The flux (Ag/cm2 h) of nicorandil was calculated

from the slope of the plot of the cumulative amount of

nicorandil permeated per cm2 of skin membrane at

steady state against the time using linear regression

analysis [11,28]. The steady state permeability coeffi-

cient (kp) of the drug through rat epidermis was

calculated by using the following equation [29]:

kp=J/C, where J is the flux and C is the concentration

of nicorandil in the gel.

The plasma concentration of nicorandil at differ-

ent time intervals was subjected to pharmacokinetic

analysis to calculate various parameters such as

maximum plasma concentration (Cmax), time to

reach maximum concentration (Tmax) and area

under the curve (AUC0–24 h). The values of Cmax

and Tmax were directly read from the arithmetic plot


of time versus plasma concentration of nicorandil.

The area under the curve of time versus plasma

concentration of nicorandil (AUC0–24 h) was calcu-

lated by using trapezoidal rule.

2.1.12. Statistical analysis

The statistical significance of the observed differ-

ence in the permeation of nicorandil across excised rat

skin, EVA2825 membrane, adhesive-coated EVA2825

membrane and adhesive-coated EVA2825-mem-

brane–rat-skin composite was tested by using analysis

of variance (ANOVA) with Bonferoni test for multiple

comparison using SPSSn computer program (PC Ver-

sion 12.0, SPSS Inc., 1989–2003). The variance in the

values of pharmacokinetic parameters was tested for

equality of variance; on acceptance of the hypothesis,

paired t-test was used to test the statistical significance

of the observed difference in pharmacokinetic para-

meters of nicorandil after the application of nerodilol-

based TTS and immediate release tablet dosage form.

The t-test with unequal variances was used to test the

significance. In all the cases, a value of P b0.05 was

considered statistically significant.

3. Results and discussion

To prepare a membrane-moderated TTS, the HMPC

gel drug reservoir is to be sandwiched between a drug-

impermeable backing laminate and a rate-controlling

polymeric membrane. The rate-controlling membranes

can be either a microporous or a nonporous polymer.

Ethylene vinyl acetate (EVA) copolymer with 28%

vinyl acetate content (EVA2825) was chosen as the

rate-controlling membrane because of its excellent

film-forming properties, good water-vapor transmis-

sion and appreciable tensile strength (Technical Bro-

chure on EVA copolymers: Nature and properties,

supplied by M/s. National Organic Chemical Indus-

tries Limited [NOCIL], Mumbai, India). Also the se-

lection of EVA2825 as rate-controlling membrane was

based on our earlier reports [30,31].

A pressure-sensitive adhesive coat on the rate-con-

trolling membrane (EVA2825) is necessary to provide

an intimate contact of the membrane-moderated TTS

to the skin such that the drug permeation takes place

through skin from the drug reservoir system. Three

types of pressure-sensitive adhesives are commonly

used in the design of TTS: polyisobutylenes, polysi-

loxanes and polyacrylic copolymers [32]. The acylic

polymers gained much commercial acceptance.

Hence, it is proposed to choose a commercially avail-

able water-based acrylic adhesive emulsion (TACK-

WHITE A 4MEDR) as a pressure-sensitive adhesive

in the design of membrane-moderated TTS of nicor-

andil. But, the coat of pressure-sensitive adhesive

(TACKWHITE A 4MEDR) applied over the rate-

controlling EVA2825 membrane offers its own resis-

tance to the permeation of nicorandil. The selection of

TACKWHITE A 4MEDR pressure-sensitive adhesive

is also based on our earlier report involving the study

on three commercially available pressure-sensitive

adhesives [30,31].

The results of the entire study were expressed as

meanFS.D. The thickness of the EVA2825 mem-

branes was found to be 24.4F0.7 Am. The low

standard deviation (0.7 Am) around mean value of

24.4 Am indicates uniformity of thickness of the

prepared EVA2825 membrane. On application of the

adhesive coat, the thickness of the coated membrane

was found to be 42.2F0.9 Am. This shows that the

thickness applied adhesive coat was 17.8 Am.

Excised rat skin was used as a skin model for

studying the in vitro permeation of nicorandil from a

nerodilol-based HPMC drug reservoir system. Al-

though human cadaver skin may be the logical

choice as a skin model for the final product to be

used in humans, it is not easily available for most of

the investigators. It is more appropriate to use the

skin of hairless mouse, hairless rat or pig as approx-

imate substitute for human skin. Nevertheless, the in

vitro permeation studies using the excised rat skin

provide information to manipulate the design of a

TTS patch for achieving the desired permeation of

the drug across human skin. This was based on the

extent of relationship between rat skin permeability

when compared to human skin. The permeability of

rat skin was reported to be about 3 times more than

that of human skin [33].

3.1. Influence of rate-controlling EVA2825 membrane

and adhesive-coated EVA2825 membrane on the in

vitro permeation of nicorandil

The cumulative amount of nicorandil permeated

from HPMC gel containing 4% w/w of drug (nicor-

Table 1

Meanw (FS.D.) in vitro permeation parameters of nicorandil from

nerodilol-based HPMC gel drug reservoir across excised rat skin,

EVA2825 membrane, adhesive coated EVA2825 membrane and

adhesive-coated EVA2825-membrane–rat-skin composite

Membrane/

skin

J

(Ag/cm2 h)

kp(cm/h�10�3)a

Cumulative

amount (Ag/cm2)

of drug permeated

at the end of

24 h (Q24)

Excised

rat skin

(control)

384.0F4.6 9.60F0.12 9333.2F129.4

EVA2825 222.7F7.1b 5.57F0.18b 5268.5F224.6b

Adhesive-coated

EVA2825

183.8F5.7a 4.60F0.15a 4378.7F122.1a

Adhesive-coated

EVA2825-rat

skin composite

164.8F1.8c 4.12F0.04c 3853.6F108.9c

w : Mean of three experiments.a Significant at P b0.001 when compared to control.b Significant at P b0.001 when compared to EVA2825.c Significant at P b0.001 when compared to adhesive-coated

EVA2825.

0 5 10 15 20 250

2000

4000

6000

8000

10000

Excised rat skin

EVA2825 membrane

Adhesive-coated EVA2825 membrane

Adhesive-coated EVA2825

membrane-rat skin composite

Am

ount

of n

icor

andi

l per

mea

ted

(µg/

cm2 )

Time (h)

Fig. 1. Mean (FS.D.) amount of nicorandil permeated from

nerodilol-based HPMC gel drug reservoir across excised rat skin,

EVA2825 membrane, adhesive-coated EVA2825 membrane and ad-

hesive-coated EVA2825-rat skin composite (n =3).


andil) and 10% w/w of nerodilol across EVA2825

membrane (thickness=24.4F0.7 Am), adhesive-coat-

ed EVA2825 membrane and adhesive-coated

EVA2825-membrane–rat-skin composite was shown

in Fig. 1. The amount of nicorandil permeated across

EVA2825 membrane from nerodilol-based drug res-

ervoir was 5268.5F224.6 Ag/cm2, and on application

of the adhesive coat, the amount of drug permeated

decreased significantly (P b0.001) to 4378.7F122.1

Ag/cm2 indicating that the pressure-sensitive adhesive

coat offered its own resistance to the permeation of

nicorandil. The amount of nicorandil permeated de-

creased further to 3853.6F108.9 Ag/cm2 (significant

at P b0.001) on application of the adhesive-coated

EVA2825 to excised rat skin (adhesive-coated

EVA2825-membrane–rat-skin composite).

The permeation of nicorandil across EVA2825

membrane, adhesive-coated EVA2825 membrane

and adhesive-coated EVA2825-membrane–rat-skin

composite was linear (Fig. 1). However, the perme-

ation of nicorandil across rat skin (control) from the

nerodilol-based HPMC gel drug reservoir was not

linear beyond 12 h. This appears due to the high

penetration enhancing activity of nerodilol on rat

skin, which in turn reduced the concentration of

nicorandil in HPMC gel reservoir. The flux of nicor-

andil with 10% w/w of nerodilol in the drug reservoir

across the excised rat skin was 384.0F4.6 Ag/cm2

h wherein the flux across EVA2825 membrane signif-

icantly decreased (P b0.001) to 222.7F7.1 Ag/cm2

h (Table 1) indicating that the EVA2825 membrane

controlled the permeation of nicorandil. The perme-

ability coefficient (kp) of nicorandil across EVA2825

membrane also decreased significantly (P b0.001)

when compared to that obtained from excised rat

skin. The permeability coefficient of nicorandil across

excised rat skin was 9.60F0.12 cm/h X 10-3, but it

decreased significantly (P b0.001) to 5.57F0.18 cm/

h�10-3 through EVA2825 membrane. The results of

the in vitro permeation study with EVA2825 mem-

brane indicated that EVA2825 is acting as a rate-

controlling membrane for the controlled delivery of

nicorandil from HPMC drug reservoir system contain-

ing nerodilol as penetration enhancer.

The flux of nicorandil across EVA2825 membrane

further decreased significantly (P b0.001) to 183.8F


5.7 Ag/cm2 h when an adhesive coat of (coat thickness

17.8 Am) was applied over EVA2825 membrane.

When the adhesive-coated EVA2825 membrane was

stuck to the excised rat skin (adhesive-coated

EVA2825-membrane–rat-skin composite), the flux of

nicorandil further decreased significantly (P b0.001)

to 164.8F1.8 Ag/cm2 h. The permeability coefficient

(kp) and Q24 of nicorandil across the adhesive-coated

EVA2825 membrane-excised rat skin composite were

also decreased significantly (P b0.001) when com-

pared to that obtained from adhesive-coated

EVA2825 membrane. The permeability coefficient

of nicorandil across adhesive-coated EVA2825 mem-

brane was 4.60F0.15 cm/h�10-3, but it was only

4.12F0.04 cm/h�10-3 through the adhesive-coated

EVA2825-membrane–rat-skin composite. Similar re-

sult was observed with respect to the amount of drug

permeated from EVA2825 at the end of 24 h (Q24) of

study (Table 1). Thus, the results of the in vitro

permeation studies from nerodilol-based HPMC gel

drug reservoir across EVA2825 membrane, adhesive-

coated EVA2825 membrane and adhesive-coated

EVA2825-membrane–rat-skin composite showed that

EVA2825 was effective as brate-controlling mem-

braneQ. The drug flux across the composite of adhe-

sive-coated EVA2825 membrane rat skin significantly

decreased when compared to that of adhesive-coated

EVA2825 membrane. Based on the mean flux of the

drug obtained across various membranes (Table 1),

there was only 10% of decrease in the flux of the

drug across rat skin when compared to that from

adhesive-coated EVA2825 membrane. This might be

due to poor contact of adhesive-coated EVA2825

membrane to rat skin during the in vitro permeation

study.

The flux of nicorandil across the composite of

adhesive-coated EVA2825 rat skin was 1.74 times

more than the required flux (94.7 Ag/cm2 h). Still,

the in vitro permeation data obtained using animal

skin model (excised rat skin) could not be extrapolat-

ed to human skin to conclude the usefulness of the

nerodilol-based membrane-moderated TTS of nicor-

andil. But, the studies so far carried out provided

enough evidence to carry out a study on the bioavail-

ability of nerodilol-based TTS of nicorandil in human

volunteers to investigate their ability in providing the

desired plasma concentration of the drug for the pre-

determined period of time.

3.2. Area of nerodilol-based TTS

The required flux of nicorandil across excised rat

skin, for optimizing the formulation of TTS, was

calculated for an exposed area of 6.6 cm2 [24]. How-

ever, the permeability of rat skin was reported to be

about 3 times more than that of human skin [33].

Also, the oral bioavailability of nicorandil is only

75% [20]. Hence, on application of the proposed

TTS to human skin, the extent of nicorandil flux

obtained across excised rat skin may not be achieved

in humans with the exposed transdermal area of 6.6

cm2 used in the in vitro permeation studies. Also, the

in vitro permeation studies through the adhesive-coat-

ed EVA2825-membrane–rat-skin composite showed

only 1.74 times of the required flux wherein the

desired plasma concentration of the drug may not

obtained because of the possible resistance of the

human stratum corneum. Keeping in view all these

factors, the required TTS area was calculated, as

detailed below.

The flux of nicorandil across the adhesive-coated

EVA2825-membrane–rat-skin composite from nerodi-

lol-based HPMC gel drug reservoir (containing 10%

w/w of nerodilol as penetration enhancer) was

164.8F1.8 Ag/cm2 h. Based on this flux, the area of

TTS required for providing a steady state concentra-

tion of 15 ng/ml for a period of 24 h was calculated

from the daily transdermal dose of nicorandil, which

in turn was calculated based on the bioavailability and

daily oral dose of nicorandil in humans.

The total daily maximal dose of nicorandil is 20 mg,

and considering the mean oral bioavailability as 75%

[20], the calculated daily transdermal dose (bioavail-

ability� daily oral dose of nicorandil) was 15 mg. The

area of TTS required to maintain a steady state con-

centration of 15 ng/ml for 24 h period from the mem-

brane-moderated TTS in humans was calculated by

using the following relationship [33] based on the

observed mean flux (164.8 Ag/cm2 h) across the adhe-

sive-coated EVA2825-membrane–rat-skin composite:

Area of TTS=[Daily transdermal dose�3] / [t�J],

where t is the time period for which the steady state

concentration is to be maintained (24 h) and J is the

observed mean flux (164.8 Ag/cm2 h) using excised rat

skin as a skin model and b3Q is the correction factor to

be applied for predicting the permeability of the drug

in humans based on the permeability flux obtained

0 5 10 15 20 25

0

20

40

60

80

100

Immediate release tablet

Nerodilol-based TTS

Pla

sma

conc

entra

tion

of n

icor

andi

l (ng

/mL)

Time (h)

Fig. 2. Mean (FS.D.) plasma concentration of nicorandil following

the oral administration of immediate release tablet or application of

nerodilol-based TTS in human volunteers (n =6).

Table 2

Mean (FS.D.) pharmacokinetic parameters of nicorandil following

oral administration of immediate release tablet (5 mg) or application

of nerodilol-based TTS (dose 80 mg) in human volunteers (n =6)

Pharmacokinetic

parameter

Immediate release

tablet

Nerodilol-based TTS

Cmax (ng/ml) 89.0F5.3 30.9F1.0*

Tmax (h) 0.6F0.1 9.8F0.6*

AUC0–24 h (ng/h ml) 223.5F21.4 554.7F27.8*

* Significant at P b0.001 when compared to immediate release

tablet.


from excised rat skin [33]. Thus, the area of TTS

required to provide a steady state concentration of 15

ng/mL for a period of 24 h from a transdermal dose of

15 mg, based on the flux of nicorandil (164.8 Ag/cm2

h) obtained from excised rat skin, was 11.4 cm2. For

the sake of convenience, it was planned to prepare a

TTS with an area of 20 cm2. In the present study, the in

vitro permeation studies warranted for the incorpora-

tion of 80 mg of nicorandil (4% w/w) in the HPMC gel

drug reservoir so as to maintain a high concentration

gradient of the drug in HPMC gel reservoir [24]. Thus,

a total of 80 mg of nicorandil was incorporated in the

HPMC drug reservoir.

3.3. Bioavailability of nerodilol-based TTS of

nicorandil in human volunteers

The nerodilol-based TTS of nicorandil were found

to be intact without any leakage and contained about

98.5% of nicorandil indicating the content uniformity

in the nerodilol-based TTS. The drug-spiked plasma

and the plasma of the in vivo evaluation showed the

same retention times indicating that the other plasma

components did not interfere with the estimation of

nicorandil in plasma. The mean plasma concentration

of nicorandil at different time intervals following the

application of nerodilol-based TTS or oral administra-

tion of immediate release tablet dosage form was

shown in Fig. 2. On application of TTS, the plasma

concentration of nicorandil gradually increased and

attained steady state concentration with a lag period

of 3.3F0.2 h. The average steady state plasma con-

centration of nicorandil obtained with TTS was 25.5

ng/ml, which was maintained at 24 h also. The trend in

the decline of plasma concentration indicates that the

steady-state concentration of nicorandil would be

maintained beyond 24 h also with respect to the

TTS. The occurrence of a higher steady state concen-

tration of nicorandil, well within the limits of thera-

peutically relevant levels [20], at 24 h is most probably

due to the incorporation of a higher amount of the drug

incorporated in the drug reservoir (80 mg in place of

the calculated transdermal dose of 15 mg; the in vitro

permeation studies [24,25] have warranted for increas-

ing the concentration of nicorandil in HPMC drug

reservoir so as to provide a higher concentration gra-

dient). However, it may be noted that the steady state

concentration of nicorandil, observed in the present

study, was within the range of therapeutically relevant

[20] steady state concentration (15 to 30 ng/ml).

The pharmacokinetic parameters of nicorandil fol-

lowing oral administration of immediate release tablet

dosage form or application of nerodilol-based TTS are

given in Table 2. The pharmacokinetic parameters of

nicorandil after the application of TTS were signifi-

cantly (P b0.001) different from those obtained with

immediate release tablet dosage form. It took

9.8F0.6 h (Tmax) to reach maximum concentration

of 30.9F1.0 ng/ml (Cmax) from TTS. However, on

oral administration of nicorandil, as an immediate


release tablet, the Cmax (89.0F5.3 ng/ml) of the drug

reached within 0.6F0.1 h and declined rapidly.

The inter-subject variation in plasma concentration

of nicorandil after oral administration of immediate

release tablet was found high (% CV ranging from

13.7 to 28.2). The low variation (% CV ranging from

1.1 to 4.7) in peak plasma levels following transder-

mal application of nicorandil TTS could be accounted

for uniformity in the transdermal permeation of the

drug, which is possibly the same for all volunteers.

The inter-subject variation in plasma levels observed

in the volunteers receiving immediate release tablet

could be due to the high variation in gastric emptying

and GI absorption etiology of individual volunteers

[34–36]. The other possible reason is that limited

plasma samples were withdrawn at Tmax (0.6F0.1 h).

The increase in the area under the curve (AUC0 - 24 h)

of nicorandil with the nerodilol-based TTS was

found to be significantly (P b0.001) higher when

compared to oral administration of immediate release

dosage form (Table 2). The result of in vivo evalu-

ation in human volunteers showed that the nerodilol-

based membrane-moderated TTS, designed in the

present study, was found to provide prolonged steady

state plasma concentration of nicorandil with mini-

mal fluctuations.

The skin irritation and sensitization due to the ap-

plication of TTS was also assessed because severe skin

irritation may affect the efficacy or safety of the TTS

formulation. The components of TTS either alone or in

conjunction with the drug substance may cause these

reactions. Hence, the volunteers were asked to report

any sign of skin irritation during the 24 h of study.

Also, the application sites of the volunteers were ob-

served for any signs of skin irritation/sensitization at

the end of the in vivo evaluation. There were no signs

of skin irritancy after the application of the TTS for one

day. Even none of the volunteers reported any skin

irritancy indicating that the nerodilol-based TTS, de-

veloped in the present study, were well tolerated for

one day. However, the possibility of skin irritancy on

long-term usage of these TTS needs to be studied. The

TTS showed 90% adhesion as there was no bno liftingQof the TTS from the skin. Thus, the results of the in

vivo pharmacokinetic evaluation of the membrane-

moderated TTS in human volunteers prompt for further

studies in patient volunteers suffering from angina

pectoris in providing an effective and safe therapy.

4. Conclusions

The in vitro permeation study from a nerodilol-

based HPMC drug reservoir across excised rat skin

(control), EVA2825 membrane, adhesive-coated

EVA2825 membrane and adhesive-coated EVA2825-

membrane–rat-skin composite showed that EVA2825

membrane was effectively controlling the release of

nicorandil. When the nerodilol-based TTS of nicor-

andil was tested in human volunteers, it provided the

desired plasma concentration of nicorandil for the

predetermined period with minimal fluctuation.

Acknowledgements

The authors acknowledge M/s. NOCIL, Mumbai,

India, M/s 3M drug delivery systems, USA and M/s

Ichemco, Italy for the gift samples of EVA copoly-

mers, Release liner (3Mk Scotchpakk 1022), back-

ing membrane (3Mk Scotchpakk 9732) and

TACKWHITE A 4MEDR, respectively. The authors

acknowledge M/s Dr. Reddy’s Laboratories Pvt. Ltd.,

Hyderabad, India for the gift sample of HPMC.

References

[1] M.R. Prausnitz, S. Mitragotri, R. Langer, Current status and

future potential of transdermal drug delivery, Nat. Rev. Drug

Discov. 3 (2004) 115–124.

[2] J.A. Bouwstra, G.S. Gooris, J.A. van der Spek, W. Bras,

Structural investigations of human stratum corneum by

small-angle X-ray scattering, J. Invest. Dermatol. 97 (1991)

1005–1012.

[3] P.M. Elias, The stratum corneum revisited, J. Dermatol. 23

(1996) 756–758.

[4] A.C. Williams, B.W. Barry, Penetration enhancers, Adv. Drug

Deliv. Rev. 56 (2004) 603–618.

[5] B.B. Michniak, M.R. Player, J.M. Chapman, J.W. Sowell,

Azone analogues as penetration enhancers: effect of different

vehicles on hydrocortisone acetate skin permeation and reten-

tion, J. Control. Release 32 (1994) 147–154.

[6] S. Sato, Y. Hirotani, N. Ogura, E. Sasaki, S. Kitagawa, En-

hancing effect of N-dodecyl-2-pyrrolidone on the percutane-

ous absorption of 5-fluorouracil derivatives, Chem. Pharm.

Bull. 46 (1998) 831–836.

[7] H. Tanojo, J.A. Bouwstra, H.E. Junginger, H.E. Bodde, In

vitro human skin barrier modulation by fatty acids: skin

permeation and thermal analysis studies, Pharm. Res. 14

(1997) 42–49.


[8] Y. Morimoto, Y. Wada, T. Seki, K. Sugibayashi, In vitro skin

permeation of morphine hydrochloride during the finite appli-

cation of penetration-enhancing system containing water, eth-

anol and l-menthol, Biol. Pharm. Bull. 25 (2002) 134–136.

[9] T. Akimoto, K. Kawahara, Y. Nagasem, T. Aoyagi, Polymeric

transdermal drug penetration enhancer: enhancing effect of

oligodimethylsiloxane containing a glucopyranosyl end

group, J. Control. Release 77 (2001) 49–57.

[10] M. Endo, T. Yamamoto, T. Ijuin, Effect of nonionic surfactants

on the percutaneous absorption tenoxicam, Chem. Pharm.

Bull. 44 (1996) 865–867.

[11] M.A. Yamane, A.C. Williams, B.W. Barry, Terpene penetra-

tion enhancers in propylene glycol/water co-solvent systems:

effectiveness and mechanism of action, J. Pharm. Pharmacol.

47 (1995) 978–989.

[12] K. Zhao, S. Singh, J. Singh, Effect of menthone on the in vitro

percutaneous absorption of tamoxifen and skin reversibility,

Int. J. Pharm. 219 (2001) 177–181.

[13] H.K. Vaddi, P.C. Ho, S.Y. Chan, Terpenes in propylene glycol as

skin-penetration enhancers: permeation and partition of halo-

peridol, Fourier transform infrared spectroscopy, and differen-

tial scanning calorimetry, J. Pharm. Sci. 91 (2002) 1639–1651.

[14] S. Gao, J. Singh, In vitro percutaneous absorption enhance-

ment of lipophilic drug tamoxifen by terpenes, J. Control.

Release 51 (1998) 193–199.

[15] K. Zhao, J. Singh, In vitro percutaneous absorption en-

hancement of propranolol hydrochloride through porcine

epidermis by terpenes/ethanol, J. Control. Release 62

(1999) 359–366.

[16] K. Zhao, J. Singh, Mechanisms of percutaneous absorption of

tamoxifen by terpenes: eugenol, d-nerodilol and menthone, J.

Control. Release 55 (1998) 253–260.

[17] A.F. El-Kattan, C.S. Asbill, N. Kim, B.B. Michniak, The

effects of terpene enhancers on the percutaneous permeation

of drugs with different lipophilicities, Int. J. Pharm. 215 (2001)

229–240.

[18] J. Frampton, M.M. Buckley, A. Fitton, Nicorandil, a review of

its pharmacology and therapeutic efficacy in angina pectoris,

Drugs 44 (1992) 625–655.

[19] D.M. Kerins, R.M. Robertson, D. Robertson, Drugs used for

the treatment of myocardial ischemia, in: J.G. Hardman, L.E.

Limbird (Eds.), Goodman and Gilman’s The Pharmacological

Basis of Therapeutics, 10th ed., McGraw Hill Medical Pub-

lishing Division, New York, 2001, p. 864.

[20] A. Frydman, Pharmacokinetic profile of nicorandil in humans:

an overview, J. Cardiovasc. Pharmacol. 20 (Suppl 3) (1992)

S34–S44.

[21] K. Sato, K. Sugibayashi, Y. Morimoto, Species differences in

percutaneous absorption of nicorandil, J. Pharm. Sci. 80

(1991) 104–107.

[22] K. Sato, K. Sugibayashi, Y. Morimoto, H. Omiya, N. Eno-

moto, Prediction of the in-vitro human skin permeability of

nicorandil from animal data, J. Pharm. Pharmacol. 41 (1989)

379–383.

[23] D.N. Tipre, P.R. Vavia, Formulation optimization and stability

study of transdermal therapeutic system of nicorandil, Pharm.

Dev. Technol. 7 (2002) 325–332.

[24] S.M. Al-Saidan, Y.S.R. Krishnaiah, D.V. Chandrasekhar, J.K.

Lalla, B. Rama, B. Jayaram, P. Bhaskar, Formulation of an

HPMC gel drug reservoir system with ethanol–water as a

solvent system and nerodilol as a penetration enhancer for

enhancing in vitro transdermal delivery of nicorandil, Skin

Pharmacol. Appl. Skin Physiol. 17 (2004) 310–320.

[25] Y.S.R. Krishnaiah, S.M. Al-Saidan, D.V. Chandrasekhar,

J.K. Lalla, Effect of nerodilol and carvone on the in vitro

transdermal delivery of nicorandil, AAPS J. 6 (4) (2004)

(Abstract W4263).

[26] P.R. Keshary, Y.W. Chien, Mechanism of transdermal con-

trolled nitroglycerin administration: Part 2. Assessment of

rate controlling steps, Drug Dev. Ind. Pharm. 10 (1984)

1663–1699.

[27] W.L. Hayton, T. Chen, Correction of perfusate concentration

for sample removal, J. Pharm. Sci. 71 (1982) 820–821.

[28] H.O. Ho, L.C. Chen, H.M. Lin, M.T. Sheu, Penetration en-

hancement by menthol combined with a solubilization effect

in a mixed solvent system, J. Control. Release 51 (1998)

301–311.

[29] A.C. Williams, B.W. Barry, Terpenes and the lipid–protein

partitioning theory of skin penetration enhancement, Pharm.

Res. 8 (1991) 17–24.

[30] Y.S.R. Krishnaiah, V. Satyanarayana, P. Bhaskar, Influence of

nerodilol on the bioavailability of nicardipine hydrochloride

from membrane-moderated transdermal therapeutic systems in

human volunteers, Int. J. Pharm. 247 (2002) 91–102.

[31] Y.S.R. Krishnaiah, V. Satyanarayana, P. Bhaskar, Influence of

menthol and pressure sensitive adhesives on the in vivo per-

formance of membrane-moderated transdermal therapeutic

system of nicardipine hydrochloride in human volunteers,

Eur. J. Pharm. Biopharm. 55 (2003) 329–337.

[32] M.C. Musolf, Pressure-sensitive adhesives: science and en-

gineering, in: Y.W. Chien (Ed.), Transdermal Controlled

Systemic Medications, Marcel Dekker, New York, 1987,

pp. 93–112.

[33] I. Diez, H. Colom, J. Moreno, R. Obach, C. Peraire, J. Dome-

nech, A comparative in vitro study of transdermal absorption

of a series of calcium channel antagonists, J. Pharm. Sci. 80

(1991) 931–934.

[34] J.N. Hunt, W.R. Spurrell, The pattern of emptying of the

human stomach, J. Physiol. 113 (1951) 157–168.

[35] J.N. Hunt, Gastric emptying and secretion in man, Physiol.

Rev. 39 (1959) 491–533.

[36] S.K. Jain, S.P. Vyas, V.K. Dixit, Effective and controlled

transdermal delivery of ephedrine, J. Control. Release 12

(1990) 257–263.

bioavailability of nerodilol-based transdermal therapeutic system of nicorandil in human volunteers

Documents