Pharmacokinetics of levonorgestrel in Indian women belonging to low socio-economic group

Interactions with oral contraceptives

The interaction of a range of different factors with the pharmacologic activity of oral contraceptives is reviewed. Pharmacokinetic interactions with oral contraceptives may occur (1) during absorption and extrahepatic circulation, (2) by interfering with protein binding, and (3) during hepatic metabolism. The hepatic mixed function oxidase system, which is mainly responsible for the metabolism of oral contraceptives, is affected by several different factors and is easily induced. Nutrition affects the activity of many drugs, but information regarding oral contraceptives is meager. Both pharmacokinetic and pharmacodynamic interactions, which may be synergistic or antagonistic, between the estrogen and gestagen components of oral contraceptives, are important, but there is no correlation between the rate of metabolism of the two components. Evidence suggests that some anticonvulsant, antibiotic, and antibacterial drugs may reduce the efficacy of oral contraceptives. Instances of interactions of other therapeutic agents are reported infrequently. The incidence of serious interactions is low and does not appear to have been reduced with low-dose oral contraceptives, probably because of large intersubject variability in the pharmacokinetics of oral contraceptives.

Pharmacokinetics and pharmacodynamics of oral contraceptive steroids: factors influencing steroid metabolism

The time-dependent alterations in the serum concentrations of ethinyl estradiol, gestodene, and 3-keto-desogestrel during treatment with 30 micrograms of ethinyl estradiol + 75 micrograms of gestodene or 30 micrograms of ethinyl estradiol + 150 micrograms of desogestrel were investigated during 12 months. The levels of gestodene and 3-keto-desogestrel increased between days 1 and 21 of each cycle, reaching maximal levels during the third and sixth cycles. The serum concentrations of gestodene were fourfold to fivefold higher than those of 3-keto-desogestrel. The ethinyl estradiol levels increased significantly between days 1 and 10 during each cycle and were significantly higher by 70% during intake of ethinyl estradiol/gestodene compared with ethinyl estradiol/desogestrel, although the dose was identical. Intake of gestodene, in addition to 35 micrograms of ethinyl estradiol + 2 mg of cyproterone acetate, caused a rise in ethinyl estradiol levels. During treatment with ethinyl estradiol/gestodene and an additional 150 micrograms of levonorgestrel, there was a continuous increase in gestodene levels, although sex hormone-binding globulin level did not change. During treatment with 30 or 35 micrograms of ethinyl estradiol and 75 micrograms of gestodene, 150 micrograms of desogestrel, or 2 mg of cyproterone acetate, there were large intraindividual and interindividual variations in the steroid levels and ratios of estrogen: progestogen levels. There was no correlation with the occurrence of intermenstrual bleedings. It is concluded that ethinyl estradiol and nortestosterone derivatives may inhibit steroid-metabolizing enzymes in the liver, which results in a rise in the serum levels of contraceptive steroids. The cause of the large intraindividual variations is as yet unknown, but it is probably from changes in steroid metabolism.

Influences of diet and nutrition on clinical pharmacokinetics

The human diet represents a complex and variable mixture of nutrients, many of which have the potential for altering the disposition of drugs. This review highlights progress from a number of laboratories illustrating nutrient influences on drug dispositions and actions. Emphasis is placed on nutritional effects on hepatic drug metabolism studied in humans. Data from animals have sometimes been difficult to extrapolate to humans, as illustrated by reports on the influences of starvation, dietary lipids, and ascorbic acid. From studies in healthy subjects it is now clear that a number of specific dietary factors can influence drug metabolism by the mixed function oxidase system and conjugating enzymes. These include dietary protein, cruciferous vegetables, charcoal-broiled beef containing polycyclic aromatic hydrocarbons, and methylxanthines. The effects of such dietary components have been demonstrated for only a limited number of drug substrates for these enzyme systems. Effects of food on bioavailability have been more widely studied, and depend greatly upon the type of drug. Malnutrition can be associated with variable but potentially important effects on the bioavailability, binding, hepatic metabolism, and renal clearance of drugs. In malnourished patients it is generally difficult to recognise the roles of individual nutrient deficiencies on drug disposition, and clinical predictors of altered pharmacokinetics for various drugs in such patients are not well defined. It is likely that many important interrelationships between nutrition and new or already marketed drugs remain to be recognised, and therefore warrant further research. Nutritional effects on drug metabolising enzymes also have implications for endogenous substances such as hormones and environmental toxins and carcinogens which are metabolised by the same or related enzyme systems, and for diseases likely to be related to the actions of such chemicals.

Bioavailability of levonorgestrel from intravaginal rings in women of low income groups

Two types of intravaginal rings (IVR) containing 50-128 mg of levonorgestrel (LNOG) and 28-60 mg of estradiol were inserted in 18 apparently normal subjects belonging to the low socioeconomic group on day 5 of the cycle. A total of 120 cycles were studied with cyclic insertion and withdrawal. Data on menstrual cycle changes were noted. For bioavailability study, blood samples were collected twice weekly for a period of one month in the first cycle in 8 women. All the plasma samples were analysed for LNOG and progestrone by RIA. Cycle control was excellent in IVR users. Expulsion of the ring was noted in 4 instances. The plasma LNOG levels were found to reach a peak level ranging from 2.7-7.5 ng/ml within 4 days after the IVR insertion. In between day 9 to 24, the plasma levels appeared to be almost steady, and once the ring was removed, the levels dropped off rapidly. The mean plasma LNOG calculated during the steady-state period of the cycle ranged from 1.6-5.1 ng/ml. These mean LNOG levels were found to be inversely correlated with skin-fold at triceps. In all the subjects ovulation was found to be inhibited, as reflected by plasma progesterone values. The range of release rates calculated from plasma steady-state values was 51-119 micrograms/day. The average release rates over the entire period of observation based on area under curve were 102-200 micrograms/day. On the other hand, the release rates obtained from the residual drug in the ring after a period of use ranged from 184-259 micrograms/day.

Pharmacokinetics of norethisterone and levonorgestrel in experimental iron deficiency anemia in rabbits

Mild-moderate anemia (hemoglobin, 10-12 g/100 ml) was induced in eight female rabbits by feeding a purified diet with low iron content over a period of 4 months and it could be maintained for a further period of 7 months. Nine control animals received the same diet supplemented with iron. Pharmacokinetics of intravenously administered contraceptive steriods, norethindrone and levonorgestrel, were determined in both control and anemic rabbits at the end of 150 and 171 days, respectively. No significant alterations were observed in the disposition of these steroids in deficient rabbits as compared to controls, indicating that mild-moderate forms of iron deficiency anemia may not influence the metabolic handling of either norethindrone or levonogestrel.

Pharmacokinetics of levonorgestrel in the rat

Levonorgestrel was administered intravenously as a bolus to adult female rats and blood samples were collected at various time intervals. Serum concentrations of levonorgestrel were measured by radioimmunoassay. Analysis of data for two- and three-compartment open models indicated that in the rat, as in the human and the rabbit, a tri-exponential equation provided a better fit of the data. The half-lives for the alpha, beta and gamma phases were 10.1 min, 42.7 min and 23.1 hours, respectively. These values were closer to those reported for women than were the half-lives reported for the rabbit. The alpha and the beta phases appeared to last for 51 min and 1.3 hours, respectively, and the gamma phase was longer than 45 hours.

Pharmacokinetics of levonorgestrel in Indian women

A low dose combination pill containing levonorgestrel 150 micrograms and ethynylestradiol 50 micrograms was administered orally to 13 women. Based on their anthropometric index they were classed as well-nourished (Group A) or undernourished (Group B). Plasma levels of levonorgestrel at various intervals after dosing were analysed by a specific radioimmunoassay and its pharmacokinetic parameters were computed. Peak plasma levels in both groups occurred within 2 h and the absorption half-lives were also similar. The decline in plasma levonorgestrel showed a tri-exponential decline in all Group A women, whereas it was biphasic in most of Group B. The pi t1/2 was lower in Group A women and the alpha-phase was found to be negligible in Group B. A significant positive correlation between elimination half-life (beta t1/2) and some of the anthropometric indices suggests a possible role of nutritional status in the metabolic handling of levonorgestrel.

Effect of food restriction (undernutrition) on pharmacokinetics of levonorgestrel in rabbits

Twelve female rabbits aged about 3-4 months were randomly divided into two groups (group A and group B) and were individually matched for their initial body weights. Animals of group A received a stock diet ad libitum while each of the animals in group B were fed 50% of the diet consumed by the corresponding matched control from group A. Pharmacokinetics of levonorgestrel were determined in all animals between 1 1/2-2 months after these diets were started, using an intravenous dose of 8-20 /uCi of 3H-levonorgestrel and 15-20 /ug of levonorgestrel per kg body weight. Urinary excretion of radioactivity was also measured in all the animals for a period of 5 days following the dose. The body weights of animals on the restricted diet were 17% lower than those of the ad lib fed animals. Haemoglobin levels and plasma albumin concentration were found to be in the normal range in both groups. There was a significant increase in Metabolic Clearance Rate (MCR) and t 1/2 pi and a decrease in elimination half-life in animals of group B as compared to those seen in animals of group A. The urinary excretion of label was found to be slightly increased in group B animals as compared to that in group A controls.

The pharmacokinetics of levonorgestrel and ethynylestradiol in women - studies with Ovran and Ovranette

A radioimmunoassay for levonorgestrel (Ng), which is applicable to plasma samples obtained from women who have taken a combination type oral contraceptive, has been developed and fully validated. Plasma concentrations of Ng rise to a peak of 3.6 ng/ml after an oral dose of 150 microgram and to 5.0 ng/ml after a 250 microgram dose. Following the intravenous administration of Ng, plasma concentrations of the steroid decline bi-exponentially with mean half-lives of 0.76 and 11.55 hours. Comparison of the results of the intravenous and oral administration of the steroid show a mean systemic bioavailability of 89% after the 150 microgram dose and 99% after a 250 microgram dose. This difference was not statistically significant. The values for volume of distribution were approximately half and the values for plasma clearance three times less than that previously reported for norethindrone. The plasma ethynylestradiol levels were also measured following administration of 30 microgram both intravenously and orally. The bioavailability and kinetics were similar to that previously reported for a 50 microgram dose. The peak values after oral dosing were 103 pg/ml and were reached by 1.0 hour in all subjects.

The rabbit as an animal model to study pharmacokinetics of levonorgestrel in women

In an attempt to develop an animal model to facilitate investigations on the effects of various nutritional and environmental factors on the metabolism of the contraceptive steroid levonorgestrel, the pharmacokinetics of levonorgestrel were investigated in rabbits. Six adult female rabbits received an intravenous bolus dose of 3H-levonorgestrel, 8-20 microCi, with 15-20 micrograms of carrier cold levonorgestrel per kg body weight. Blood samples were drawn at different intervals of time after the dose and the plasma drug concentration was determined both by radioisotopic dilution method and by radioimmunoassay. Plasma concentrations of levonorgestrel as assayed by radioimmunoassay agreed very closely with those obtained by isotope counting. The decline in plasma radioactivity attributable to unchanged levonorgestrel followed a triexponential pattern. Plasma radioactivity data were therefore analysed according to a three-compartment open model by graphical and regression analysis. The half-lives of the three phases pi, alpha and beta representing the shallow, deep peripheral and the terminal elimination compartment, respectively, were in close agreement with those reported in women. The metabolic clearance rate (MCR) and volume of distribution (VB) of levonorgestrel expressed per unit of body weight were comparable to values reported in women. The overall observed trend of pharmacokinetics of levonorgestrel in rabbits resemble closely those seen in women. It would therefore appear that the rabbit is a suitable animal model for studying the effects of nutritional factors on the pharmacokinetics of the drug.