Contraception

Original research article

Effect of concurrently coadministered drugs on the pharmacokinetic/

pharmacodynamic profile of centchroman, a nonsteroidal oral

contraceptive, in rats

Vipul Kumara, Jawahar Lala,4, Man Mohan Singhb, Ram Chandra Guptaa

aPharmacokinetics and Metabolism Division, Central Drug Research Institute, PO Box 173, Lucknow 226001, IndiabEndocrinology Division, Central Drug Research Institute, Lucknow 226001, India

Received 29 December 2005; revised 16 February 2006; accepted 16 February 2006

Abstract

Introduction: Centchroman (international nonproprietary name: ormeloxifene) is a nonsteroidal selective estrogen receptor modulator, oral

contraceptive, anticancer and antiosteoporotic agent that is intended for long-term use by women. In view of the vast clinical applications and

interactions of steroidal oral contraceptives with commonly used therapeutic agents, the interaction potential of certain concomitantly

administered therapeutic agents was investigated in terms of postcoital contraceptive efficacy (pharmacological) and the pharmacokinetic

profile of centchroman in female Sprague–Dawley rats. The coadministered drugs used in the study were ciprofloxacin, cefixime,

amoxicillin, metronidazole, amlodipine, atenolol, theophylline, metformin, pioglitazone and glibenclamide.

Materials and Methods: The pharmacological activity of centchroman was evaluated in sperm-positive female rats at 1.5 mg/kg, with or

without coadministered drugs. Rats were sacrificed on Day 10 postcoitus, and autopsy was performed to check for the presence or absence of

implantations. The estrogenic and antiestrogenic activities of centchroman were evaluated in immature ovariectomized rats. Pharmacokinetic

interaction was studied in normal female rats with or without coadministered drugs. Serum samples were taken over 120 h and analyzed

using a validated high-performance liquid chromatography method to generate the pharmacokinetic profile of centchroman. Pharmacokinetic

parameters were estimated using noncompartmental analysis, and the results were compared.

Results: In pharmacological interaction studies, centchroman alone showed a 100% success rate when given alone or in the presence of

coadministered drugs. The only exception was amoxicillin coadministration, with 66% rats in the group showing resorbed implantations.

Further investigation with amoxicillin in ovariectomized immature rats indicates no alteration in the estrogenic and antiestrogenic profiles of

centchroman. In pharmacokinetic interaction studies, most of the therapeutic agents affected the rate and extent of absorption of centchroman.

In other pharmacokinetic parameters, clearance (CL) remained unchanged; however, there was decrease in bioavailability (F) and volume of

distribution (Vd) in some situations.

Conclusions: The results indicate that there is no direct link between the altered pharmacokinetics of centchroman and the failure of

pharmacological effect. The pharmacological interaction with amoxicillin could not be explained on the basis of alteration in the estrogenic and

antiestrogenic activities of centchroman, indicating that different mechanisms are involved. The findings, however, suggest that amoxicillin

coadministration may result in pharmacological interaction with centchroman and that caution should be taken in clinical practice.

D 2006 Elsevier Inc. All rights reserved.

Keywords: Centchroman; 7-Desmethyl centchroman; Interaction; Ciprofloxacin; Cefixime; Amoxicillin; Metronidazole; Amlodipine; Atenolol; Theophylline;

Metformin; Pioglitazone; Glibenclamide

1. Introduction

Centchroman (international nonproprietary name: orme-

loxifene; trans-7-methoxy-2,2-dimethyl-3-phenyl-4-[4-(2-

0010-7824/$ – see front matter D 2006 Elsevier Inc. All rights reserved.

doi:10.1016/j.contraception.2006.02.007

CDRI Communication no.: 6632.

4 Corresponding author. Tel.: +91 522 2612414x4377; fax: +91 522

2623405/2623938.

E-mail address: jlalcdri@rediffmail.com (J. Lal).

pyrrolidinoethoxy) phenyl] chroman hydrochloride) is a

nonsteroidal selective estrogen receptor modulator and

once-a-week oral contraceptive agent developed by the

Central Drug Research Institute (Lucknow, India) [1–4]. Its

contraceptive activity is well established in rodents and

primates, wherein a single oral dose of centchroman within

24 h of coitus successfully prevents pregnancy in rats, dogs

and rhesus monkeys, and wherein the antifertility effect of

74 (2006) 165–173

V. Kumar et al. / Contraception 74 (2006) 165–173166

centchroman is promptly reversible [3]. It inhibits implan-

tation via the inhibition of endometrial receptivity to

blastocyst signals by the antagonistic action of nidatory

estrogen without altering the concentration or secretion

pattern of nidatory estrogen, without altering the concen-

tration or secretion pattern of nidatory estrogen and

progesterone, the hypothalamo-pituitary–ovarian axis, folli-

cle maturation, ovulation, mating behavior, gamete transport

or fertilization, and preimplantation development of embry-

os [4–12]. Clinically, centchroman has been reported to

provide good pregnancy protection in women in postcoital

and weekly regimens [13,14] and is marketed in India as a

contraceptive pill [15]. Due to its potent antiestrogenic and

weak estrogenic activities [7–16], it is also effective against

advanced breast cancer [17].

In view of the widespread and long-term clinical use of

centchroman, concomitant use of other medications is

imperative in a number of clinical situations, and so are

the chances of drug interactions. Tetracycline has shown

interaction with the anti-implantation and estrogen antago-

nistic activities of centchroman in female Sprague–Dawley

rats [18,19]. In the present study, the pharmacological and

pharmacokinetic interaction potential of certain therapeutic

agents of different classes — namely, antibiotics (cipro-

floxacin, cefixime, amoxicillin and metronidazole), anti-

asthmatics (theophylline), antihypertensives (amlodipine,

atenolol) and antidiabetics (metformin, glibenclamide and

pioglitazone) — that may be commonly used with centchro-

man was evaluated with a view that this may provide useful

baseline data for clinical situations. The study assessed

pharmacological interactions in terms of postcoital contra-

ceptive efficacy (pharmacological), and the effects of

pharmacokinetic interactions in the presence or absence of

coadministered drugs on the pharmacokinetic characteristics

of centchroman.

2. Materials and methods

2.1. Chemicals

Centchroman (purity N99%) was obtained from the

Medicinal Chemistry Division of the Central Drug Re-

search Institute. In-house-synthesized 7-desmethyl cen-

tchroman (7-DMC; purity N99%) was used. Pure

standards of coadministered drugs — namely, ciprofloxacin

HCl (Dr. Reddy’s Laboratories, Hyderabad, India), cefix-

ime trihydrate (Dhanuka Laboratories Ltd., New Delhi,

India), amoxicillin trihydrate (Khandelwal Laboratories

Ltd., Mumbai, India), metronidazole (Albert David Ltd.,

Kolkata, India), amlodipine besylate (Cadila Healthcare

Ltd., Ahemdabad, India), atenolol (Dabur Research Foun-

dation, Ghaziabad, India), theophylline (German Remidies

Ltd., Mumbai, India), metformin HCl (Wallace Pharma-

ceuticals Ltd., Goa, India), glibenclamide (Nicholas Pira-

mal India Ltd., Pithampur, India) and pioglitazone HCl

(Zydus Cadila Healthcare Ltd., Ahmedabad, India), all for

oral administration — were obtained as gift samples.

Potassium dihydrogen orthophosphate (analytical grade),

potassium hydroxide (analytical grade) and orthophos-

phoric acid (ExcelR grade) were procured from commercial

sources, and all organic solvents were of high-performance

liquid chromatography (HPLC) grade. Diethyl ether was

distilled before use.

2.2. Animals

Young adult male and female Sprague–Dawley rats

(210F20 g), maintained under standard in-house conditions,

were obtained from the Laboratory Animal Division of the

Central Drug Research Institute. They were given a standard

pellet diet (Lipton India Ltd., Bangalore) and tap water ad

libitum. All experiments, euthanasia and the disposal of

carcasses were carried out in accordance with the guidelines

laid down by the Local Ethics Committee for Animal

Experimentation. Care was taken to minimize trauma

resulting from pain during all surgical procedures, and

blood sampling was performed under ether anesthesia,

taking suitable preoperative and postoperative care.

Male and female rats were co-caged overnight in a 1:3

ratio. On the following morning, the female rats were

observed (by microscopic examination) for the presence of

sperm in their vaginal smears. Sperm-positive female rats

were isolated and used for the study. The day when the

presence of sperm was observed was considered Day 1

postcoitus (pc). Sperm-positive female rats were randomly

divided into four groups: Groups A, B, C and D. Groups C

and D consisted of 10 subgroups. Each group/subgroup

contained six rats. The pharmacokinetics of centchroman

was investigated in normal female Sprague–Dawley rats

(220F20 g). Tests of the estrogenic and antiestrogenic

activities of centchromanwere performed in immature female

rats, which were bilaterally ovariectomized under light ether

anesthesia and were given postoperative rest for 7 days.

2.3. Preparation of formulations and doses

The dose and the dosage form of centchroman and

coadministered drugs are listed in Table 1. The rat dose of

coadministered drug was calculated from the standard

clinical human dose on the basis of surface area [rat

dose={(human dose/average body weight)�7}] [20]. All

coadministered drugs were suitably formulated as solution/

suspension for oral administration. To minimize the effect of

hydrodynamics on drug absorption, the total volume of

centchroman and coadministered drugs was maintained at a

level not exceeding 5 mL/kg.

2.4. Pharmacological interaction study

For pharmacological interaction studies, sperm-positive

rats were given vehicle (25% ethanol in water), centchroman

alone (1.5 mg/kg), centchroman and drug to be coadminis-

tered, or the coadministered drug alone on Day 1 pc.

Centchroman was given as a single dose on Day 1 pc only,

while the other drugs were given up to 5 days pc as per

Table 1

Dosing schedule and the formulation of centchroman and coadministered

drugs

Serial

number

Drug Dosing schedule Formulation

1 Centchroman 1.5 mg/kg, po,

single dose,

on Day 1 pc

Solution

2 Ciprofloxacin 70 mg/kg, po,

single dose,

on Day 1 pc

Solution

3 Cefixime 56 mg/kg, po,

single dose,

on Day 1 pc

Solution

4 Amoxicillin 70 mg/kg, bid,

on Days 1–5 pc

Suspension

5 Metronidazole 56 mg/kg, bid,

on Days 1–5 pc

Suspension

6 Amlodipine 1.4 mg/kg, once daily,

on Days 1–5 pc

Suspension

7 Atenolol 7 mg/kg, once daily,

on Days 1–5 pc

Solution

8 Theophylline 84 mg/kg, bid,

on Days 1–5 pc

Suspension

9 Metformin 70 mg/kg, bid,

on Days 1–5 pc

Solution

10 Pioglitazone 6.3 mg/kg, once daily,

on Days 1–5 pc

Suspension

11 Glibenclamide 1.05 mg/kg, bid,

on Days 1–5 pc

Suspension

V. Kumar et al. / Contraception 74 (2006) 165–173 167

schedule (Tables 1 and 2). The first dose of the coadminis-

tered drug was administered ~10 min after the centchroman

dose. On Day 10 pc, the rats were sacrificed using deep ether

anesthesia, and autopsy was performed. The rats were

Table 2

Effect of coadministered drugs on the postcoital anti-implantation activity of cen

Group Treatment Pregnant/t

A Vehicle 6/6

B Centchroman 0/6

C

1 Centchroman+ciprofloxacin 0/6

2 Centchroman+cefixime 0/6

3 Centchroman+amoxicillin 4/6

4 Centchroman+metronidazole 0/6

5 Centchroman+amlodipine 0/6

6 Centchroman+atenolol 0/6

7 Centchroman+theophylline 0/6

8 Centchroman+metformin 0/6

9 Centchroman+pioglitazone 0/6

10 Centchroman+glibenclamide 0/6

D

1 Ciprofloxacin 6/6

2 Cefixime 6/6

3 Amoxicillin 6/6

4 Metronidazole 6/6

5 Amlodipine 6/6

6 Atenolol 6/6

7 Theophylline 6/6

8 Metformin 6/6

9 Pioglitazone 6/6

10 Glibenclamide 6/6

a Day 10 pc.

autopsied for the presence or absence of implantations, for

the status of corpora lutea on both sides and for body weight.

The presence of normal and/or resorbed implantations in the

uteri of Group C/D rats versus the absence of the same in

Group B rats was kept as the criterion of pharmacological

interaction/failure in the presence of the coadministered

drug. The absence of normal or resorbed implantations in

rats of Groups B and C vis-a-vis the presence of the same in

Group D rats was regarded as contraceptive efficacy. The

presence of implantations in Group A rats was used to judge

the effect of vehicle, if any, on the implantation and accuracy

of the screening procedure.

2.5. Estrogen agonistic and antagonistic activities

Twenty-one-day-old immature female rats were bilater-

ally ovariectomized under light ether anesthesia and, after

postoperative rest for 7 days, were randomized into different

treatment groups. For estrogen agonistic activity, each rat

received a single anti-implantation dose of centchroman

(1.5 mg/kg) and/or the coadministered drug on Day 28 of

age, as scheduled in Table 1, but the dose of the coadmi-

nistered drug was restricted to 3 days. For estrogen antago-

nistic activity, each rat, in addition, received 0.02 mg/kg

17a-ethinyl estradiol in 10% ethanol–water, once daily, for

3 days. Separate groups of animals receiving only the

vehicle, centchroman, 17a-ethinyl estradiol and amoxicillin

served as controls. Autopsy was performed on Day 31; the

vaginal smear of each rat was taken and the uterus was

carefully excised, gently blotted and weighed. The change

in uterine weight was used as a measure of the estrogenic

and antiestrogenic activities of centchroman.

tchroman in rats

reated rats Corpora luteaa Implantationsa

72 54

66 0

62 0

60 0

72 22

65 0

63 0

78 0

90 0

69 0

86 0

70 0

59 27

58 28

72 44

73 34

70 33

73 34

83 53

62 39

78 34

67 31

Table 3

Effect of amoxicillin coadministration on the estrogenic and antiestrogenic

activities of centchroman in ovariectomized immature rats

Treatment Uterine weight

(mg/10 g body weight)

Vehicle 4.2F0.3

Centchroman 8.1F0.44

17a-Ethinyl estradiol 25.3F2.0

Amoxicillin 6.3F0.4

Centchroman+17a-ethinyl estradiol 15.3F0.7

Amoxicillin+17a-ethinyl estradiol 24.3F0.3

Centchroman+amoxicillin 7.1F1.14

Centchroman+17a-ethinyl

estradiol+amoxicillin

16.5F0.6

4 No statistically significant difference observed ( p N .05).

V. Kumar et al. / Contraception 74 (2006) 165–173168

2.6. Pharmacokinetic interaction study

Overnight-fasted young adult female Sprague–Dawley

rats were administered a single oral contraceptive dose of

centchroman (1.5 mg/kg) with or without coadministered

drugs. The first dose of the coadministered drug was

administered ~10 min after the centchroman dose and was

continued up to 5 days, as per the dosing schedule in Table 1.

Blood samples were collected at 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8,

12, 18, 24, 48, 72, 96 and 120 h postdose. Not more than two

blood samples from each rat were withdrawn: one intracar-

dially (~1.2 mL per time point) and one from the vena cava.

Blood was allowed to clot in sealed glass tubes and

centrifuged at 2000 rpm to separate the serum. Serum

samples were stored at �608C pending analysis.

2.7. HPLC analysis

An HPLC pump system with a flow control valve and a

system controller (Shimadzu, Japan) and a syringe loading

injector (Model 7125i; Rheodyne, Cotati, CA, USA) fitted

with a fixed 50-AL loop were used. The serum levels of

centchroman and 7-DMC were quantified using a modified

HPLC assay method [21]. Briefly, serum (0.5 mL) was

basified with potassium hydroxide solution (0.5 mL, 0.2 M)

and extracted twice with diethyl ether. The combined

organic layer was evaporated to dryness under vacuum.

The dried residue was reconstituted in 0.1 mL of mobile

phase (65% acetonitrile in KH2PO4, 20 mM, pH 3.0) and

analyzed by HPLC equipped with a Brownlee 5-Am Cyano

column (220�4.6 mm i.d.) preceded with a guard column

(30�4.6 mm i.d.). Detection was performed using a

fluorescence detector (RF-10AXL; Shimadzu) set at excita-

tion (280 nm) and emission (310 nm) wavelengths.

Unknown concentrations of centchroman and 7-DMC were

interpolated from the respective serum standard curves

drawn on each day of sample analysis.

2.8. Data analysis

For postcoital contraceptive efficacy study, counts of

corpora lutea and implantations were tabulated, and efficacy

failure was determined in terms of the percentage of rats

showing implantations. For studies on estrogenic and

antiestrogenic activities, the uterine weight (in mg/10 g body

weight) of rats was recorded. Analyses of statistically signi-

ficant differences among different groups were performed

using Student’s t test ( pb .05).

In pharmacokinetic studies, the concentrations of cen-

tchroman and 7-DMC in serum samples were interpolated

from serum standard curves using linear regression analysis

(Microsoft Excel software; Microsoft Corporation, USA).

Peak serum concentration (Cmax) and the time of its

occurrence (tmax) were read directly from raw data by

visual examination of the respective mean concentration–

time profile. Centchroman concentration–time data were

subjected to noncompartmental analysis using WinNonlin

software (version 1.5) to calculate various pharmacokinetic

parameters. A minimum of three data points was used

to calculate terminal half-life as t1/2=ln(2)/kz, where kz is

the elimination rate constant. Mean residence time (MRT)

was calculated as MRT=AUMCInf/AUCInf, whereas bio-

availability (F) was calculated as F=(Doseiv�AUCpo)/

(Dosepo�AUCiv). Clearance (CL) and volume of distribu-

tion (Vd) were calculated from CL=F�Dose/AUCInf and

Vd=F�Dose/kzAUCInf, where AUC was calculated by

trapezoidal rule. The AUC until infinity was extrapolated

as Clast/kz, where Clast is the last measurable concentration

and kz represents the terminal elimination rate constant.

AUC0–last was calculated using the method of Bailer [22].

The data were compared using Student’s t test with the

Behrens–Fischer procedure [23].

3. Results and discussion

3.1. Pharmacological interaction study

The postcoital contraceptive efficacy of centchroman and

the influence of various coadministered drugs on the

postcoital contraceptive efficacy of centchroman are sum-

marized in Table 2. The autopsy of rats treated with a single

contraceptive dose (1.5 mg/kg on Day 1 pc) of centchroman

(Group B) did not show any implantations, confirming the

efficacy of the compound per se and the formulation used.

However, rats receiving vehicle only (Group A) showed

normal implantations, indicating that the vehicle had no role

in the anti-implantation effect of centchroman. Rats of

Group D, which were treated orally with coadministered

drugs alone, ciprofloxacin (70 mg/kg, single dose, on Day 1

pc), cefixime (56 mg/kg, single dose, on Day 1 pc),

metronidazole (56 mg/kg, bid, on Days 1–5 pc), amlodipine

(1.4 mg/kg, once daily, on Days 1–5 pc), atenolol (7 mg/kg,

once daily, on Days 1–5 pc), theophylline (84 mg/kg, bid,

on Days 1–5 pc), metformin (70 mg/kg, bid, on Days 1–5

pc), pioglitazone (6.3 mg/kg, once daily, on Days 1–5 pc) or

glibenclamide (1.05 mg/kg, bid, on Days 1–5 pc), showed

normal numbers and status of implantations and corpora

lutea, indicating that these drugs per se do not have any

effect on pregnancy in rats. Moreover, no implantations

Fig. 1. Concentration–time (meanFS.E.M.) profile of centchroman after a

single oral dose of 1.5 mg/kg alone and with coadministration of

ciprofloxacin and cefixime in rats (n =3).

V. Kumar et al. / Contraception 74 (2006) 165–173 169

were observed in rats of Group C treated with centchroman

plus the above coadministered drugs. These results suggest

that there is no interaction between centchroman and these

drugs in the dosing schedule used as far as the contraceptive

efficacy of centchroman is concerned. However, amoxicillin

coadministration (70 mg/kg, bid, on Days 1–5 pc; Group C)

exhibited interaction with the postcoital contraceptive

efficacy of centchroman, as evidenced by the presence of

resorbed implantations in ~66% of the rats. Moreover,

Group D rats treated with amoxicillin alone showed normal

implantations, indicating that the resorbed implantations are

due to pharmacological interactions between the two drugs.

To further probe for the observed efficacy failure in

amoxicillin coadministration, the estrogenic and antiestro-

genic activities of centchroman in the presence of amoxi-

cillin were tested in immature ovariectomized rats. The rats

Table 4

Pharmacokinetic parameters of centchroman with coadministration of antibiotics

Parameters CC, iva CC, po 1

Cmax (ng/mL)

1 – 59.5F2.1 12.2F2 – 48.0F2.3 33.6Ftmax (h)

1 – 1.5 0.75

2 – 6 6

t1/2 (h) 28 31 36

MRT (h) 30 35 51

MAT (h) – 5 21

AUC0–24 h (ng h/mL) – 795 477

AUC0–last (ng h/mL)b – 1391F27 1182FAUC0–l (ng h/mL) 5065 1465 1310

F – 0.72 0.64

Vd (L/kg) 30 32 39

CL (L/h/kg) 0.74 0.73 0.73

CC=centchroman.

(1) CC+ciprofloxacin; (2) CC+cefixime; (3) CC+amoxicillin; (4) CC+metronidaza Unpublished data.b Bailer’s method for AUC variance.

4 Significant difference ( pb .05).

(n=3 per group) were divided into eight groups for different

treatments, and the observations are shown in Table 3. The

estrogenic activity of centchroman alone was intact, as

evidenced by a significant increase in uterine weight in

comparison to the vehicle-treated group. The antiestrogenic

activity of centchroman was evident as a significant decrease

in the uterine weights of rats treated with centchroman and

17a-ethinyl estradiol versus rats treated with 17a-ethinyl

estradiol alone ( pb .001). The uterine weights of rats treated

with amoxicillin did not show significant differences when

compared with the vehicle-treated group, indicating that

amoxicillin is no different from the vehicle as far as

estrogenicity and antiestrogenicity are concerned. The rats

treated with centchroman and amoxicillin did not show

significant differences in uterine weight when compared

with the centchroman-treated group. These results indicate

that amoxicillin coadministration did not affect the estro-

genic and antiestrogenic activities of centchroman and that

some other mechanisms may be responsible for the

observed pharmacological interaction.

3.2. Pharmacokinetic interaction study

In female rats, the pharmacokinetic parameters of

centchroman at its contraceptive dose were generated as a

rule of thumb for baseline information. Thereafter, the phar-

macokinetics of centchroman was investigated in the

presence of different coadministered drugs. Following a

single oral dose of centchroman with or without coadminis-

tered drugs, serum levels of centchroman and 7-DMC were

determined using the HPLC assay. The assay method was

validated before use. The limit of quantification in rat serum

was determined to be 1.25 and 3.75 ng/mL, respectively. A

linear relationship existed between the peak heights and con-

centrations of centchroman (6.25–250 ng/mL) and 7-DMC

(18.75–750 ng/mL) in the mobile phase and the serum

in rats

2 3 4

1.94 39.8F4.94 60.1F3.2 25.4F2.24

3.4 22.1F0.84 – 17.9F3.04

2 4 3

12 – 24

37 33 36

51 42 57

21 12 27

505 577 321

43 1106F304 1082F394 1085F394

1234 1172 1226

0.61 0.57 0.60

39 35 39

0.74 0.74 0.73

ole.

Fig. 2. Concentration–time (meanFS.E.M.) profile of centchroman after a

single oral dose of 1.5 mg/kg alone and with coadministration of

amoxicillin and metronidazole in rats (n =3).

V. Kumar et al. / Contraception 74 (2006) 165–173170

concentrations of centchroman (1.25–50 ng/mL) and 7-DMC

(3.75–150 ng/mL), respectively. The recovery of centchro-

man and 7-DMC ranged from 83% to 88% and from 89% to

94%, respectively. For both centchroman and 7-DMC,

between-assay bias, within-assay bias, interbatch precision

and intrabatch precision were within acceptable limits in

quality control samples (n=3) at low, medium and high

concentration levels (centchroman: 2.5, 10 and 50 ng/mL,

respectively; 7-DMC: 7.5, 30 and 150 ng/mL, respectively).

Following a single oral dose of 1.5 mg/kg centchroman

alone, the parent drug was monitored up to 120 h. The

serum concentration–time (meanFS.E.M.) profile of cen-

tchroman after a single oral administration is shown in

Fig. 1. A visual examination of the concentration–time data

revealed that centchroman exhibited twoCmax values (Cmax 1:

59.5F2.1 ng/mL; Cmax 2: 48.0F2.3 ng/mL) at 1.5 and 6 h,

respectively. Due to irregularity in the serum concentration–

time profile of centchroman, its pharmacokinetic parameters

Fig. 3. Concentration–time (meanFS.E.M.) profile of centchroman after a

single oral dose of 1.5 mg/kg alone and with coadministration of

amlodipine and atenolol in rats (n =3).

were obtained by noncompartmental analysis of the data and

are listed in Table 4. Volume of distribution (Vd=32 L/kg)

and clearance (CL=0.73 L/h/kg) were in agreement with

the values obtained after a 3.75-mg/kg intravenous injec-

tion of centchroman (unpublished data; Table 4). Bioavail-

ability factor (F), calculated from F=(Doseiv�AUCpo)/

(Dosepo�AUCiv), was found to be 0.72.

The occurrence of more than one peak has been reported

with a number of drugs [24–30], and several mechanisms

[31–33] have been proposed as underlying causes. Enter-

ohepatic recycling has been ruled out as the major causative

factor for the double peak of centchroman [19]. The high

logP value (7.04) [34] and the weak basic nature of

centchroman (pKa=2.1) [35] indicate that its slow dissolu-

tion in the gastrointestinal tract acts as the rate-limiting

factor in its absorption. Extremely high and low logP values

have been reported to result in the poor absorption of drugs

because of resultant extreme lipophilicity and the hydro-

philic nature of the drugs, respectively [36]. This is further

supported by the fact that, after oral administration of radio-

labeled centchroman, 10% of the radioactive dose of centch-

roman was present in stomach washings and 55% was

present in intestinal washings after 24 h of administration

[37]. The MRT of the percent radioactivity in the stomach,

as calculated from these data, was found to be ~6 h, which is

the normal gastric transit rate in rats [38]. The double peak

of centchroman in most tissues, such as in hepatic, adipose

and uterine tissues, at 1 h and between 8 and 12 h [34] further

supports this axiom. Furthermore, the clearance of centchro-

man (0.73 L/h/kg) is approximately one third of the hepatic

blood flow in rats (2 L/h/kg) [38], showing that it is slowly

cleared from the body.

The serum concentration–time profile of 7-DMC was

highly irregular and variable. 7-DMC started appearing in

the systemic circulation at 1 h and could be quantified until

72 h after the centchroman dose. The AUC0–l for 7-DMC

was found to be 474 ng h/mL.

Fig. 4. Concentration–time (meanFS.E.M.) profile of centchroman after a

single oral dose of 1.5 mg/kg alone and with coadministration of

theophylline and metformin in rats (n =3).

Fig. 5. Concentration–time (meanFS.E.M.) profile of centchroman after a

single oral dose of 1.5 mg/kg alone and with coadministration of

glibenclamide and pioglitazone in rats (n =3).

V. Kumar et al. / Contraception 74 (2006) 165–173 171

The comparative pharmacokinetic profiles of centchro-

man with and without coadministered drugs are shown in

Figs. 1–5. It was observed that most of the coadministered

drugs resulted in altered rates of absorption of centchroman,

as evident from the shift in tmax and different Cmax values

(Tables 4 and 5). Both the rate and extent of absorption of

centchroman were affected by the coadministered drugs, as

evidenced by significant differences ( pb .05) in Cmax and

AUC0–last in comparison to controls (Tables 4 and 5). The

alteration in the absorption of centchroman can be explained

by the fact that absorption is the first pharmacokinetic

process that is affected when two drugs are coadministered.

Further analysis of AUC0–24 h also supports this observa-

tion. Metronidazole coadministration had a major affect on

the rate of absorption of centchroman, which was evident

Table 5

Pharmacokinetic parameters of centchroman with coadministration of antihyperte

Parameters 1 2 3

Cmax (ng/mL)

1 45.0F2.14 38.9F3.34 26.

2 23.7F1.34 36.4F2.8 30.

3 – – 24.

tmax (h)

1 1.5 1 1.5

2 18 6 6

3 – – 12

t1/2 (h) 29 28 21

MRT (h) 38 37 29

MAT (h) 8 7 –

AUC0–24 h (ng h/mL) 609 495 480

AUC0–last (ng h/mL)a 1167F214 896F324 853

AUC0–l (ng h/mL) 1235 944 889

F 0.61 0.47 0.4

Vd (L/kg) 31 30 23

CL (L/h/kg) 0.73 0.74 0.7

CC=centchroman.

(1) CC+amlodipine; (2) CC+atenolol; (3) CC+theophylline; (4) CC+metformin; (a Bailer’s method for AUC variance.

4 Significant difference ( p b .05).

from the low Cmax and the delayed tmax (Table 4). Although

coadministered drugs reduced the bioavailable fraction (F)

of centchroman, there were no observations of efficacy

failure that can be directly linked to low bioavailability. In

the case of amoxicillin, which showed a pharmacological

interaction with centchroman, there was a decrease in the

bioavailability of centchroman; however, this could be

considered a reason for the pharmacological interaction

because there were other drugs wherein the decrease in

bioavailability was greater than that observed with amox-

icillin coadministration but wherein no effect on the

pharmacological activity of centchroman was observed

(Table 5). An important pharmacokinetic parameter (CL)

remained unchanged with the coadministered drugs. This

indicates that coadministered drugs do not interfere with

pathways responsible for the CL of centchroman. The Vd

was unchanged in most of the cases, although coadminis-

tration of theophylline and pioglitazone resulted in a

decrease in Vd, but it seemed to have no effect on the

concentrations of centchroman in target tissues, as the

pharmacological effect of centchroman was intact when

either of the two drugs was coadministered. In all cases, the

7-DMC metabolite of centchroman exhibited a highly

variable and irregular profile, which in turn can be attributed

to alteration in the absorption profile of centchroman,

thereby affecting the rate of metabolism.

To summarize, this study describes the influence of the

coadministration of various commonly used drugs on the

pharmacological and pharmacokinetic profiles of centchro-

man at its contraceptive dose in rats. The results revealed

that the pharmacological activity of centchroman remained

unaltered with the coadministration of ciprofloxacin, cefix-

ime, metronidazole, amlodipine, atenolol, theophylline,

metformin, pioglitazone and glibenclamide when adminis-

nsive, antiasthmatic and antidiabetic agents in rats

4 5 6

5F5.94 49.4F3.94 39.5F3.74 26.0F4.04

7F2.44 60.9F4.84 45.5F2.8 46.8F5.8

4F4.5 18.7F1.0 – –

1 2 1

3 4 4

18 – –

28 20 33

41 29 45

11 – 15

565 610 560

F264 989F164 1103F334 1270F60

1070 1145 1371

3 0.52 0.56 0.67

30 21 35

4 0.74 0.74 0.73

5) CC+pioglitazone; (6) CC+glibenclamide.

V. Kumar et al. / Contraception 74 (2006) 165–173172

tered on Days 1–5 pc. The pharmacokinetic interaction

study showed that coadministered drugs result in variations

in the rate and extent of absorption of centchroman and in its

distribution, but that the clearance of centchroman remained

unaltered. However, although amoxicillin interfered with the

contraceptive efficacy of centchroman, amoxicillin coad-

ministration had no effect on the estrogenic and antiestro-

genic activities of centchroman. The results suggest that

changes in the pharmacokinetic profile of centchroman

cannot be related directly to pharmacological effects. The

interaction of amoxicillin is not related to pharmacokinetic

interactions arising from changes in the estrogenic and

antiestrogenic profiles of centchroman. It is therefore

proposed that some other mechanism is involved in the

efficacy failure of centchroman and that caution is needed in

the use of amoxicillin coadministration with centchroman in

clinical practice. Further clinical investigations are neces-

sary to confirm these findings.

Acknowledgments

The authors thank Dr. C.M. Gupta, Director of the

Central Drug Research Institute, for allowing the use of

facilities. The financial assistance extended by the Council

of Scientific and Industrial Research, India, to one of the

authors (V.K.) is gratefully acknowledged. The technical

assistance provided by Ms. Deepali Rathore (Pharmacoki-

netics Division) and Ms. Mohini Chabra, and the help

rendered by Mr. Jagdish Prasad and Mr. B.P. Misra

(Endocrinology Division) are acknowledged.

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