Clinical pharmacokinetics of oral contraceptive steroids

Estrogen contamination increases vulnerability of amphibians to the deadly chytrid fungus

Aquatic contaminants and infectious diseases are among the major drivers of global amphibian declines. However, the interaction of these factors is poorly explored and could better explain the amphibian crisis. We exposed males and females of the Brazilian Cururu Toad, Rhinella icterica, to an environmentally relevant concentration of the estrogen 17-alpha-ethinylestradiol (an emerging contaminant) and to the chytrid infection (Batrachochytrium dendrobatidis), in their combined and isolated forms, and the ecotoxicity was determined by multiple biomarkers: cutaneous, hematological, cardiac, hepatic, and gonadal analysis. Our results showed that Cururu toads had many physiological alterations in response to the chytrid infection, including the appearance of cutaneous Langerhans's cells, increased blood leukocytes, increased heart contraction force and tachycardia, increased hepatic melanomacrophage cells, which in turn led to gonadal atrophy. The estrogen, in turn, increased the susceptibility of the toads to the chytrid infection (higher Bd loads) and maximized the deleterious effects of the pathogen: reducing leukocytes, decreasing the contraction force, and causing greater tachycardia, increasing hepatic melanomacrophage cells, and leading to greater gonadal atrophy, which were more extreme in females. The exposure to estrogen also revealed important toxicodynamic pathways of this toxicant, as shown by the immunosuppression of exposed animals, and the induction of the first stages of feminization in males, which corroborates that the synthetic estrogen acts as an endocrine disruptor. Such an intricate relationship is unprecedented and reinforces the importance of studying the serious consequences that multiple environmental stressors can cause to aquatic populations.

Comparison of estrogenic components used for hormonal contraception

Attempts have been made over the years to replace ethinyl estradiol (EE) in combined oral contraceptives (COCs) with the less potent natural estrogen estradiol (E2), or its prodrug, E2 valerate (E2V), to improve their safety and tolerability. Recently, a COC incorporating a novel weak natural estrogen, estetrol (E4), combined with drospirenone, has become available. We present a comparative analysis of the three prevailing estrogens used in COCs, focusing on their structure-function relationships, receptor-binding affinity, potency, metabolism, pharmacokinetic parameters, and pharmacodynamics. The binding affinity of EE to estrogen receptor (ER)α is twice that of E2, whereas its affinity for ERβ is about one-half that of E2. E4 has a lower binding affinity for the ERs than E2. The high potency of EE is notable in its dramatic increase in estrogen-sensitive hepatic globulins and coagulation factors. EE and E2 undergo extensive and comparable metabolism, while E4 produces only a very limited number of metabolites. E4 has the highest bioavailability among the three estrogens, with E2 having <5%. Studies demonstrate consistent ovulation inhibition, although a higher dose of E4 (15 mg) in COCs is required to achieve follicular suppression compared to E2 (1-3 mg) and EE (0.01-0.035 mg). E2 and E4 in COCs may be less stimulatory of coagulant proteins than EE. Studies with E2/dienogest suggest a comparable risk of venous thromboembolism to EE/levonorgestrel, while data assessing risk with an E4-based COC are insufficient. Nevertheless, the E4-based formulation shows promise as a potential alternative to EE and E2 due to its lower potency and possibly fewer side effects.

Drug-Drug Interaction Studies With Oral Contraceptives: Pharmacokinetic/Pharmacodynamic and Study Design Considerations

Oral contraceptives (OCs) are the most widely used form of birth control among women of childbearing potential. Knowledge of potential drug-drug interactions (DDIs) with OCs becomes imperative to provide information on the medication to women of childbearing potential and enable their inclusion in clinical trials, especially if the new molecular entity is a teratogen. Although a number of DDI guidance documents are available, they do not provide recommendations for the design and conduct of OC DDI studies. The evaluation of DDI potential of a new molecular entity and OCs is particularly challenging because of the availability of a wide variety of combinations of hormonal contraceptives, different doses of the ethinyl estradiol, and different metabolic profiles of the progestin component. The aim of this review is to comprehensively discuss factors to be considered such as pharmacokinetics (PK), pharmacodynamics (PD), choice of OC, and study population for the conduct of in vivo OC DDI studies. In this context, metabolic pathways of OCs, the effect of enzyme inhibitors and inducers, the role of sex hormone-binding globulin in the PK of progestins, current evidence on OC DDIs, and the interpretation of PD end points are reviewed. With the emergence of new tools like physiologically based PK modeling, the decision to conduct an in vivo study can be made with much more confidence. This review provides a comprehensive overview of various factors that need to be considered in designing OC DDI studies and recommends PK-based DDI studies with PK end points as adequate measures to establish clinical drug interaction and measurement of PD end points when there is basis for PD interaction.

Rationalizing Steroid Interactions with Lipid Membranes: Conformations, Partitioning, and Kinetics

Steroids have numerous physiological functions associated with cellular signaling or modulation of the lipid membrane structure and dynamics, and as such, they have found broad pharmacological applications. Steroid-membrane interactions are relevant to multiple steps of steroid biosynthesis and action, as steroids are known to interact with neurotransmitter or membrane steroid receptors, and steroids must cross lipid membranes to exert their physiological functions. Therefore, rationalizing steroid function requires understanding of steroid-membrane interactions. We combined molecular dynamics simulations and isothermal titration calorimetry to characterize the conformations and the energetics of partitioning, in addition to the kinetics of flip-flop transitions and membrane exit, of 26 representative steroid compounds in a model lipid membrane. The steroid classes covered in this study include birth control and anabolic drugs, sex and corticosteroid hormones, neuroactive steroids, as well as steroids modulating the lipid membrane structure. We found that the conformational ensembles adopted by different steroids vary greatly, as quantified by their distributions of tilt angles and insertion depths into the membrane, ranging from well-defined steroid conformations with orientations either parallel or normal to the membrane, to wide conformational distributions. Surprisingly, despite their chemical diversity, the membrane/water partition coefficient is similar among most steroids, except for structural steroids such as cholesterol, leading to similar rates for exiting the membrane. By contrast, the rates of steroid flip-flop vary by at least 9 orders of magnitude, revealing that flip-flop is the rate-limiting step during cellular uptake of polar steroids. This study lays the ground for a quantitative understanding of steroid-membrane interactions, and it will hence be of use for studies of steroid biosynthesis and function as well as for the development and usage of steroids in a pharmacological context.

Postpartum intrauterine devices: clinical and programmatic review

The immediate postpartum period is a critical moment for contraceptive access and an opportunity to initiate long-acting reversible contraception, which includes the insertion of an intrauterine device. The use of the intrauterine device in the postpartum period is a safe practice with few contraindications and many benefits. Although an intrauterine device placed during the postpartum period is more likely to expel compared with one placed at the postpartum visit, women who initiate intrauterine devices at the time of delivery are also more likely to continue to use an intrauterine device compared with women who plan to follow up for an interval intrauterine device insertion. This review will focus on the most recent clinical and programmatic updates on postpartum intrauterine device practice. We discuss postpartum intrauterine device expulsion and continuation, eligibility criteria and contraindications, safety in regards to breastfeeding, and barriers to access. Our aim is to summarize evidence related to postpartum intrauterine devices and encourage those involved in the healthcare system to remove barriers to this worthwhile practice.

Influence of the Gastrointestinal Environment on the Bioavailability of Ethinyl Estradiol Sorbed to Single-Walled Carbon Nanotubes

Recent evidence suggests that, because of their sorptive nature, if single-walled carbon nanotubes (SWCNTs) make their way into aquatic environments, they may reduce the toxicity of other waterborne contaminants. However, few studies have examined whether contaminants remain adsorbed following ingestion by aquatic organisms. The objective of this study was to examine the bioavailability and bioactivity of ethinyl estradiol (EE2) sorbed onto SWCNTs in a fish gastrointestinal (GI) tract. Sorption experiments indicated that SWCNTs effectively adsorbed EE2, but the chemical was still able to bind and activate soluble estrogen receptors (ERs) in vitro. However, centrifugation to remove SWCNTs and adsorbed EE2 significantly reduced ER activity compared to that of EE2 alone. Additionally, the presence of SWCNTs did not reduce the extent of EE2-driven induction of vitellogenin 1 in vivo compared to the levels in organisms exposed to EE2 alone. These results suggest that while SWCNTs adsorb EE2 from aqueous solutions, under biological conditions EE2 can desorb and retain bioactivity. Additional results indicate that interactions with gastrointestinal proteins may decrease the level of adsorption of estrogen to SWCNTs by 5%. This study presents valuable data for elucidating how SWCNTs interact with chemicals that are already present in our aquatic environments, which is essential for determining their potential health risk.

Lack of a Pharmacokinetic Interaction Between SYM-1219 Granules Containing 2 Grams of Secnidazole and a Combined Oral Contraceptive in a Phase 1, Randomized, Open-Label Study in Healthy Female Volunteers

INTRODUCTION

Bacterial vaginosis (BV) is a serious infection that is the most common vaginal infection in women of childbearing potential. SYM-1219 is a novel, granule formulation containing 2 g of secnidazole that is being developed as a single, oral dose to treat women with BV. Because many of the women diagnosed with BV use hormonal contraception, the effect of SYM-1219 on the pharmacokinetics (PK) of commonly prescribed oral contraceptive drugs, ethinyl estradiol (EE2), and norethindrone (NET) was evaluated.

METHODS

This two-period, randomized, open-label study examined effects in 54 healthy female subjects. During the first period of the study, each subject received EE2 0.035-mg/NET 1-mg tablets. During the second period of the study, subjects were randomized to receive either EE2 0.035-mg/NET 1-mg tablets with concomitant 2-g SYM-1219 or 2-g SYM-1219 followed by EE2 0.035-mg/NET 1-mg tablets 1 day later. The PK of EE2 and NET were analyzed for 24 h following administration.

RESULTS

Coadministration of SYM-1219 and EE2/NET, either on the same day or 1 day apart, had no clinically relevant effects on the bioavailability of EE2 or NET. The combined use of SYM-1219 with EE2/NET was well tolerated. Taken together, these results indicate that contraceptive efficacy should be maintained during coadministration of SYM-1219 and EE2/NET.

CONCLUSION

SYM-1219 is a valuable single-dose treatment option for women with BV that will not interfere with combined oral contraceptive methods.

FUNDING

Symbiomix Therapeutics.

Endocrine-Modulating Substances in the Environment: Estrogenic Effects of Pharmaceutical Products

Several classes of anthropogenic substances modulate endocrine pathways. To date, most of the research has focused on chemical classes such as chlorinated hydrocarbon contaminants, pesticides, or degradation products of high-use industrial surfactants. However, little is known about the environmental impact of another important class of chem icals: hormonally active pharmaceutical products. This deficit of information is surprising, given the biological potencies of these widely used substances and their potential to enter the environment through sewage treatment effluents and runoff from agricultural applications. Estrogenic pharmaceutical products are used extensively in human estrogen-replacement therapy and oral contraceptive formulations. Estrogenic substances are also used as growth enhancement products in veterinary medicine. This report describes the potencies, pharm acokinetics, and metabolic pathways of such estrogenic products. The amounts of pharmaceutical-derived estrogens that reach the environment from doses and usage are estimated. Factors that affect environmental concentrations including metabolism and biodegradation are also considered. Finally, we present both chemical and analytical data, as well as bioassay evidence, that suggest that biologically active concentrations of estrogenic compounds are being released into the aquatic environment.

Analysis of steroid hormones and their conjugated forms in water and urine by on-line solid-phase extraction coupled to liquid chromatography tandem mass spectrometry

Background

In recent years, endocrine disrupting compounds (EDCs) have been found in rivers that receive significant inputs of wastewater. Among EDCs, natural and synthetic steroid hormones are recognized for their potential to mimic or interfere with normal hormonal functions (development, growth and reproduction), even at ultratrace levels (ng L⁻¹). Although conjugated hormones are less active than free hormones, they can be cleaved and release the unconjugated estrogens through microbial processes before or during the treatment of wastewater. Due to the need to identify and quantify these compounds, a new fully automated method was developed for the simultaneous determination of the two forms of several steroid hormones (free and conjugated) in different water matrixes and in urine.

Results

The method is based on online solid phase extraction coupled with liquid chromatography and tandem mass spectrometry (SPE–LC–MS/MS). Several parameters were assessed in order to optimize the efficiency of the method, such as the type and flow rate of the mobile phase, the various SPE columns, chromatography as well as different sources and ionization modes for MS. The method demonstrated good linearity (R² > 0.993) and precision with a coefficient of variance of less than 10 %. The quantification limits vary from a minimum of 3–15 ng L⁻¹ for an injection volume of 1 and 5 mL, respectively, with the recovery values of the compounds varying from 72 to 117 %.

Conclusion

The suggested method has been validated and successfully applied for the simultaneous analysis of several steroid hormones in different water matrixes and in urine.

Electronic supplementary material

The online version of this article (doi:10.1186/s13065-016-0174-z) contains supplementary material, which is available to authorized users.

17α-Ethinylestradiol can disrupt hemoglobin catabolism in amphibians

Different chemical substances, which enter the environment due to anthropogenic influences, can affect the endocrine system and influence development and physiology of aquatic animals. One of these endocrine disrupting chemicals is the synthetic estrogen, 17α-ethinylestradiol (EE2), which is a main component of various oral contraceptives and demonstrably affects many different aquatic vertebrates at extremely low concentrations by feminization phenomena. The aim of the present study was to investigate whether a four week exposure to three different concentrations of EE2 (0.3 ng/L, 29.6 ng/L and 2960 ng/L) affects the catabolism of hemoglobin of the amphibian Xenopus laevis. The results of this study demonstrate for the first time that beside an increase of the hepatic vitellogenin gene expression, exposure to EE2 also decreases the gene expression of the hepatic heme oxygenase 1 and 2 (HO1, HO2), degrading heme of different heme proteins to biliverdin, as well as of the biliverdin reductase A (BLVRA), which converts biliverdin to bilirubin. The results further suggest that EE2 already at the environmentally relevant concentration of (29.6 ng/L) can disrupt hemoglobin catabolism, indicated by decreased gene expression of HO2, which becomes evident at the highest EE2 concentration that led to a severe increase of biliverdin in plasma.

Concomitant Administration of Lumiracoxib and a Triphasic Oral Contraceptive Does Not Affect Contraceptive Activity or Pharmacokinetic Profile

This study evaluated the effect of lumiracoxib on the pharmacokinetics and pharmacodynamics of ethinyl estradiol (EE) and levonorgestrel (LN) in Triphasil-28 (a triphasic oral contraceptive). Females stabilized on Triphasil-28 continued on Triphasil-28 alone for another month (Treatment Period 1), then also received lumiracoxib (400 mg daily) or placebo for 28 days each (Periods 2 and 3) in a double-blind crossover design. Plasma pharmacokinetic profiles were assessed on Day 21 of Periods 2 and 3. Progesterone and plasma sex hormone binding globulin (SHBG) concentrations were measured before and 2 hours after Triphasil-28 administration on Day 21 of all three treatment periods. Lumiracoxib had no significant effect on EE or LN pharmacokinetics or on progesterone or SHBG concentrations, indicating that anovulation and Triphasil-28 effectiveness was maintained. Adverse events were similar for lumiracoxib and placebo. Therefore, no clinically important consequences are anticipated if lumiracoxib is coadministered with oral contraceptives containing EE or LN.

Estrogens can disrupt amphibian mating behavior

The main component of classical contraceptives, 17α-ethinylestradiol (EE2), has high estrogenic activity even at environmentally relevant concentrations. Although estrogenic endocrine disrupting compounds are assumed to contribute to the worldwide decline of amphibian populations by adverse effects on sexual differentiation, evidence for EE2 affecting amphibian mating behaviour is lacking. In this study, we demonstrate that EE2 exposure at five different concentrations (0.296 ng/L, 2.96 ng/L, 29.64 ng/L, 2.96 µg/L and 296.4 µg/L) can disrupt the mating behavior of adult male Xenopus laevis. EE2 exposure at all concentrations lowered male sexual arousal, indicated by decreased proportions of advertisement calls and increased proportions of the call type rasping, which characterizes a sexually unaroused state of a male. Additionally, EE2 at all tested concentrations affected temporal and spectral parameters of the advertisement calls, respectively. The classical and highly sensitive biomarker vitellogenin, on the other hand, was only induced at concentrations equal or higher than 2.96 µg/L. If kept under control conditions after a 96 h EE2 exposure (2.96 µg/L), alterations of male advertisement calls vanish gradually within 6 weeks and result in a lower sexual attractiveness of EE2 exposed males toward females as demonstrated by female choice experiments. These findings indicate that exposure to environmentally relevant EE2 concentrations can directly disrupt male mate calling behavior of X. laevis and can indirectly affect the mating behavior of females. The results suggest the possibility that EE2 exposure could reduce the reproductive success of EE2 exposed animals and these effects might contribute to the global problem of amphibian decline.

Pharmacokinetic Drug Interactions Involving 17??-Ethinylestradiol

17alpha-Ethinylestradiol (EE) is widely used as the estrogenic component of oral contraceptives (OC). In vitro and in vivo metabolism studies indicate that EE is extensively metabolised, primarily via intestinal sulfation and hepatic oxidation, glucuronidation and sulfation. Cytochrome P450 (CYP)3A4-mediated EE 2-hydroxylation is the major pathway of oxidative metabolism of EE. For some time it has been known that inducers of drug-metabolising enzymes (such as the CYP3A4 inducer rifampicin [rifampin]) can lead to breakthrough bleeding and contraceptive failure. Conversely, inhibitors of drug-metabolising enzymes can give rise to elevated EE plasma concentrations and increased risks of vascular disease and hypertension. In vitro studies have also shown that EE inhibits a number of human CYP enzymes, such as CYP2C19, CYP3A4 and CYP2B6. Consequently, there are numerous reports in the literature describing EE-containing OC formulations as perpetrators of pharmacokinetic drug interactions. Because EE may participate in multiple pharmacokinetic drug interactions as either a victim or perpetrator, pharmaceutical companies routinely conduct clinical drug interaction studies with EE-containing OCs when evaluating new chemical entities in development. It is therefore critical to understand the mechanisms underlying these drug interactions. Such an understanding can enable the interpretation of clinical data and lead to a greater appreciation of the profile of the drug by physicians, clinicians and regulators. This article summarises what is known of the drug-metabolising enzymes and transporters governing the metabolism, disposition and excretion of EE. An effort is made to relate this information to known clinical drug-drug interactions. The inhibition and induction of drug-metabolising enzymes by EE is also reviewed.

Distribution of estrogens, 17beta-estradiol and estrone, in Canadian municipal wastewater treatment plants

The distribution of female hormones, 17beta-estradiol and estrone, was determined in effluents of 18 selected municipal treatment plants across Canada. Replicate 24-h composite samples were collected from the influent and final effluent of each treatment plant, and the removal efficiency compared to the operational characteristics of the plants. In conventional activated sludge and lagoon treatment systems, the mean concentrations of 17beta-estradiol and estrone in influent were 15.6 ng/l (range 2.4-26 ng/l) and 49 ng/l (19-78 ng/l). In final effluents, the mean concentrations of both 17beta-estradiol and estrone were reduced to 1.8 ng/l (0.2-14.7 ng/l) and 17 ng/l (1-96 ng/l), respectively. 17beta-estradiol was removed effectively, >75% and as high as 98%, in most of the conventional mechanical treatment systems with secondary treatment. The removal of estrone was much more complex with removal varying from 98% to situations where the concentrations in the effluent were elevated above that detected in the influent. The estrogenicity, measured using a transfected estrogen receptor in yeast (YES) assay, was also variable, ranging from high removal to elevations of estrogenicity in final effluent. Although the apparent removals were not statistically correlated with either hydraulic (HRT) or solid (SRT) retention times, plants or lagoons with high SRT were very effective at reducing the levels of hormones. Well-operated plants that achieved nitrification also tended to have higher removal of hormones than those that did not nitrify. Laboratory aerobic reactor experiments confirmed the rapid removal of 17beta-estradiol, estrone, and estrogenicity when exposed to sewage slurries.

Oral contraception does not alter single dose saquinavir pharmacokinetics in women

AIMS

Women experience more adverse drug reactions (ADR) to antiretroviral therapy than men. This may be attributed to higher plasma concentrations of protease inhibitors due to pharmacokinetic interactions with hormonal preparations. Thus, in the present study we aimed to investigate the influence of oral contraceptives (OC) on the pharmacokinetics of the protease inhibitor saquinavir.

METHODS

Saquinavir was administered in a hard gelatin capsule formulation (Invirase) to rule out confounding by pharmaceutical aids of the more frequently used soft gelatin capsule. After an overnight fast, eight healthy female participants ingested a single oral dose of 600 mg saquinavir immediately before and after the 19th dose of a combined, low dose OC (0.03 mg ethinylestradiol, 0.075 mg gestodene) in a prospective, fixed sequence study design. The first saquinavir application was scheduled on day 1, 2, or 3 of the individual menstrual cycle. Plasma concentrations of saquinavir and relative concentrations of its M2&M3-hydroxy metabolites were determined by LC/MS/MS for 48 h.

RESULTS

Intake of OC resulted in a significant decrease in morning serum concentrations (before intake of OC, compared to day 19 of OC therapy) of 17beta-estradiol by -23.4 pg ml-1 (57%, 95%CI: -76% to -37.4%); progesterone by -0.25 ng ml-1 (33%, 95%CI: -45.3% to -21.5%); follicle-stimulating hormone by -4.06 U l-1 (82%, 95%CI: -96.5% to -67.7%); and luteinizing hormone by -3.49 U l-1 (74%, 95%CI: -93 to -54.6%). Conversely, sexual hormone binding globulin serum concentrations increased by 83.6 nmol l-1 (205%, 95%CI: 32.2% to 377%). Pharmacokinetic parameters of saquinavir (AUC, Cmax, tmax, t1/2, CLR) were not affected by OC, nor was the relative metabolic ratio of saquinavir/M2&M3-hydroxy saquinavir. Furthermore, there was no association of serum hormone concentrations or MDR1-polymorphisms (C3435T and G2677T) with pharmacokinetic parameters of saquinavir.

CONCLUSIONS

There was no effect of OC on saquinavir pharmacokinetics. Thus, pharmacokinetic interactions of synthetic sexual steroids with saquinavir are not likely to account for the increased ADR to antiretroviral therapy seen in women.

Occurrence and analysis of estrogens and progestogens in river sediments by liquid chromatography-electrospray-mass spectrometry

In this study, an analytical procedure for the determination in sediment of the most abundant and/or physiological active estrogens (estradiol, estriol, estrone, ethynyl estradiol, and diethylstilbestrol) and progestogens (progesterone, norethindrone. and levonorgestrel) is described. The procedure includes ultrasonic extraction of the lyophilized sediment, clean-up with octadecylsilica cartridges, and analysis by liquid chromatography-diode array detection-mass spectrometry (LC-DAD-MS). MS detection is performed with an electrospray interface in the positive ion mode for determination of the progestogens and in the negative ion mode for determination of the estrogens. The method was applied to the determination of the target compounds in river sediments from the area of Catalonia. Estrogens and progestogens were found at concentrations usually in the low ng g(-1) range. Estriol and norethindrone were the compounds most frequently found whereas maximum concentrations in all sediment samples were obtained for ethynyl estradiol (22.8 ng g(-1)) and estrone (11.9 ng g(-1)). Detection limits were in the range of 0.04-1.00 ng g(-1). Preliminary conjectures with regards to the environmental behavior and impact of estrogens and progestogens in rivers are made. To the authors' knowledge, this is the first work reporting a detailed method for the analysis of estrogens and progestogens in river sediments and data on the environmental occurrence of both groups of compounds.

Effect of rofecoxib on the pharmacokinetics of chronically administered oral contraceptives in healthy female volunteers

The effect of rofecoxib, a highly selective cyclooxygenase (COX)-2 inhibitor, on the pharmacokinetics of ethinyl estradiol (EE) and norethindrone (NET), two common components of a combination oral contraceptive product, was examined. A double-blind, two-period crossover study was conducted in 18 healthy women who received ORTHO-NOVUM 1/35, a combination of EE (35 microg) and NET (1 mg), concurrently for 14 days with either 175 mg rofecoxib or matching placebo during two consecutive menstrual cycles. Plasma was sampled for EE, NET, sex hormone binding globulin (SHBG), and albumin. The AUC(0-24 h) geometric mean ratio (GMR: rofecoxib/placebo) with corresponding 90% confidence interval (CI) of EE and NET was 1.13 (1.06, 1.19) and 1.18 (1.13, 1.24), respectively. The Cmax GMR of EE and NET was 1.06 (0.98, 1.16) and 1.04 (0.99, 1.09), respectively. In each case, the 90% CIs satisfied the predefined bioequivalence limits of (0.80, 1.25). Measures of SHBG and albumin and routine clinical and laboratory safety parameters showed no clinically meaningful changes. The addition of rofecoxib to the oral contraceptive was not associated with any clinically important changes in EE or NET pharmacokinetics and thus would not be anticipated to influence the efficacy of this contraceptive regimen.

The effects of an oral contraceptive containing ethinyloestradiol and norgestrel on CYP3A activity

AIMS

To examine the effects of an oral contraceptive containing ethinyloestradiol and norgestrel on intestinal and hepatic CYP3A activity using midazolam as a probe substrate.

METHODS

In a nonblinded sequential study, nine healthy women received simultaneous doses of intravenous midazolam (0.05 mg kg(-1)) and oral 15N3-midazolam (3 mg) on days 0, 4, 6, 8, and 14. On study day 5, Ovral(50 microg ethinyloestradiol/500 microg norgestrel) was administered for 10 days. Serum and urine samples were assayed for midazolam, 15N3-midazolam and metabolites by liquid chromatography-mass spectrometry. A Digit Symbol Substitution Test (DSST) was used to assess changes in the pharmacodynamic activity of midazolam.

RESULTS

Moderate (% CV 26-46) interindividual variability in the pharmacokinetics of midazolam were observed. Compared with baseline, AUC(0,infinity)iv ratios (95% CIs) after 2, 4, and 10 days treatment with OC were 89% (79, 101), 96% (85, 109), and 88% (77, 99), respectively. The AUC(0,infinity)oral ratios (95% CIs) were 101% (82, 125), 105% (85, 130), and 114% (92, 141), respectively, after 2, 4, and 10 days OC treatment compared with baseline. Concomitant administration of the oral contraceptive, Ovral for 2, 4 or 10 days did not significantly alter the area under the curve, clearance, or half-life of midazolam after either oral or intravenous administration. No alterations in pharmacodynamic effects of midazolam were observed between treatment days. Mean DSST scores strongly correlated with mean total midazolam blood concentrations (r = -0.936).

CONCLUSIONS

Administration of Ovral for 10 days had no impact on intestinal or hepatic CYP3A activity as determined by midazolam metabolism.

Effects of the synthetic estrogen 17 alpha-ethinylestradiol on the life-cycle of the fathead minnow (Pimephales promelas)

A fish full life-cycle (FFLC) study was conducted for 17 alpha-ethinylestradiol (EE2) using the fathead minnow, Pimephales promelas. Newly fertilized embryos (< 24 h old) were exposed to five concentrations of EE2 (0.2, 1.0, 4.0, 16, and 64 ng/L nominal) in continuous flow-through conditions for 305 d at 25 +/- 1 degrees C. Exposure concentrations were verified by 14C-EE2 radiochemistry, supported by radioimmunoassay, and mean measured values were > or = 70% of nominal. For the F0 adult phase until 301 d posthatch, the no-observed-effect concentrations (NOECs) for growth, survival, and reproduction (as egg production) were all > or = 1.0 ng/L. The NOEC values for F1 embryo hatching success and larval survival (at 28 d posthatch) were both > or = 1.0 ng/L. While statistically detectable changes in F1 growth were evident at 0.2 ng/L, these were not considered to be biologically significant when compared with historical control data. Male fish exposed to EE2 at 4.0 ng/L failed to develop normal secondary sexual characteristics; on the other hand, assumed females exposed to this level of EE2 were able to breed when paired with males that had not been exposed to EE2. Histology of F0 control, 0.2-, and 1-ng/L exposed fish at 56 d posthatch indicated an approximate female-to-male (F:M) sex ratio of 50:50 (with no ovatestes observed in the control), while fish exposed to EE2 at 4.0 ng/L for 56 d posthatch had a F:M sex ratio of 84:5 (with ovatestes in 11% of fish). After 172 d posthatch, no testicular tissue was observed in any fish exposed to EE2 at 4.0 ng/L. At the same time point, plasma vitellogenin levels were significantly higher in fish exposed to EE2 at 16 ng/L. A lack of sexual differentiation occurred in males at concentrations > or = 4.0 ng/L. Taking into account these data, the overall no-observed-adverse-effect concentration was considered to be 1.0 ng/L.

Identification of UDP-glucuronosyltransferases involved in the human hepatic metabolism of GV150526, a novel glycine antagonist

The major metabolic pathway for elimination of GV150526 is by glucuronidation exerted by glucuronosyl transferases (UGTs). Potential exists for the modification of GV150526 pharmacokinetics by drugs capable of inhibiting the glucuronidation of GV150526. Using human liver microsomes, 44 compounds were screened for inhibition of GV150526 glucuronidation. These compounds were selected because they are extensively glucuronidated themselves or are used as concomitant medication in the treatment of acute stroke. For 11 compounds out of the 44, full inhibition kinetics were performed to determine their Ki-value and mechanism of inhibition. To predict possible in vivo drug-drug interactions, the theoretical percentage of inhibition (i) was determined, based on in vitro determined Ki-values, and the expected Cmax plasma levels of GV150526 and the inhibitor. Of the 11 compounds examined, only propofol had an i-value of 6.6; for all other compounds i-values were lower than 2.1. These results indicate that although in vitro inhibition is observed, the likelihood of in vivo drug-drug metabolic interactions occurring is low. The inhibition results suggest that in addition to UGT1A1, also UGT1A3, UGT1A8/9, and UGT2B4 are involved in the glucuronidation of GV150526. The involvement of UGT1A1 and UGT1A8/9 was confirmed from studies using cDNA expressed human UGT cell lines.

Hormonal properties of norethisterone, 7alpha-methyl-norethisterone and their derivatives

Norethisterone (NET) is a progestagenic compound with very weak androgenicity and estrogenicity. These low androgenic and estrogenic activities may be attributed to NET itself or induced by metabolites of NET. In order to improve the bioactivity of NET, the effects of a 7alpha-methyl substitution were studied. Thus this study has two objectives: first the comparison between biological activities of NET and 7alpha-methyl-NET (MeNET), and second the biological activity of tentative metabolites of NET and those of MeNET. The metabolites consist of a 3-keto-, 3alpha- or 3beta-hydroxy-group located next to a carbon 4 to 5 double bond (Delta(4)) or a 5alpha-hydrogen atom. The 7alpha-methyl substitution was of special interest as it prevents 5alpha-reduction. The biological activities of NET, MeNET and their potential metabolites were assessed by in vitro binding, transactivation and proliferation assays on progesterone (PR), androgen (AR), estrogen (ER) and glucocorticoid (GR) receptors and by in vivo progestagenic McPhail, androgenic Hershberger, estrogenic Allen-Doisy tests and combined estrogenic and progestagenic ovulation inhibition tests. NET is a compound with five- to eight-fold weaker PR binding and transactivation activities than the reference compound Org 2058 (100%) and two-fold stronger than progesterone. Binding and transactivation activities of NET for AR (DHT=100%) are 3.2 and 1.1%, respectively, for ER none (E2=100%) and for GR below 1% (DEX=100%). MeNET is 1.5- to two-fold less progestagenic and ten- to 20-fold more androgenic than NET, while it does not show activity for ER and GR. The relative binding affinity of 5alpha-NET was seven-fold lower for PR and 1.5-fold higher for AR than for NET, while in transactivation assays 5alpha-NET was only active at levels below 1% for all tested receptors. 3beta-Hydroxy-(5alpha-reduced)-metabolites showed clear ER binding and transactivation activities, while 3alpha-hydroxy-(5alpha-reduced)-metabolites did hardly possess these characteristics. These hydroxy metabolites did not bind or activate other receptors. Substitution of 7alpha-methyl to NET metabolites led to similar characteristics, but with higher activities for AR and ER and weaker activity for PR. The outcome of in vivo tests showed a remarkable effect for MeNET. Progestagenic activity in rabbits appeared for NET equipotent to or eight-fold higher than for MeNET, after subcutaneous or oral treatment, respectively. On the other hand, MeNET showed in rats a ten-fold higher androgenicity and eight-fold higher estrogenicity than NET. Ovulation inhibition was induced at very low oral or subcutaneous dose levels, being 120- or ten-fold lower than for NET, respectively. The estrogenicity can also be induced by 3alpha- or 3beta-hydroxy metabolites of MeNET, which are 15 or even more than 40-fold stronger than those of NET, respectively. In conclusion, after the introduction of a 7alpha-methyl substituent to NET an increased estrogenicity and androgenicity and a reduced progestagenic activity was found. The in vivo estrogenicity is mainly due to 3beta-hydroxy-MeNET and to a lesser extent to 3alpha-hydroxy-MeNET, while the androgenicity and progestagenicity are most likely caused by MeNET itself. Since the 7alpha-methyl substituent inhibits 5alpha-reductase, 5alpha-reduced MeNET metabolites can be excluded from biological activities. As MeNET is a very effective ovulation inhibitor, due to its mixed progestagenic and estrogenic profile, a further reduction of androgenicity of MeNET may yield new contraceptives with an attractive profile for contraception.

Contraceptive progestins. Various 11-substituents combined with four 17-substituents: 17alpha-ethynyl, five- and six-membered spiromethylene ethers or six-membered spiromethylene lactones

Norethisterone (NET) is a 19-nortestosterone derivative with progestagenic and some androgenic activity, which was used in the first generation of contraceptives. NET was succeeded by levonorgestrel (LNG) and later on by desogestrel (DSG) and gestodene (GSD). Although these latter two progestins had increased potency, there was still androgenicity with gestodene and to a lesser extent with desogestrel. New progestins were synthesized in order to further enhance progestagenic and to reduce androgenic activity. Four different chemical moieties were introduced in position 17 of 19-nortestosterone, viz. 17alpha-ethynyl, five- and six-membered spiromethylene ethers, and a six-membered-spiromethylene lactone. In combination with these structures seven different substituents were added at position 11, i.e. methylene, methyl, ethyl, ethenyl, ethynyl, 2-propenyl and 1-propynyl. All substituents except for methylene occupied the 11beta-position. All these 32 compounds were synthesized and analysed in vitro and in vivo against etonogestrel (ETG, 3-keto-desogestrel), the biologically active metabolite of desogestrel. Their relative binding potency to progesterone (PR), androgen (AR) and estrogen (ER) receptors were determined in cell lysates of human breast tumor MCF-7 cells and to glucocorticoid (GR) receptors in that of human leukemic IM-9 cells. Moreover, their relative agonistic activities were assessed in Chinese hamster ovary cell-based transactivation assays. All in vivo activities were determined in McPhail (progestagenic), ovulation inhibition (progestagenic and estrogenic), Hershberger (androgenic), hormone screening (glucocorticoid and estrogen) and Allen-Doisy (estrogenic) tests after oral and for the McPhail test also after subcutaneous administration. The progestagenic binding and transactivation potencies of all compounds in the three 17-spiro series were higher than those of the corresponding analogues in the 17alpha-ethynyl series. None of the compounds showed estrogenic or clear androgenic binding and transactivation potential except for a six-membered-spiromethylene lactone with a propynyl group. This compound showed strong androgenic binding. The glucocorticoid binding and transactivation were very low for the compounds with the 17alpha-ethynyl and the five-membered-spiromethylene ether groups, whereas both six-membered-spiro series showed, clearly with methyl and ethynyl substituents, and less pronounced with methylene and ethenyl, higher binding and transactivation values. For the 17alpha-ethynyl series, the McPhail test showed high potencies with methylene, methyl and ethenyl substituents after oral treatment or with propenyl after subcutaneous administration. The introduction of the spiro substituents in position 17 led to high potencies for other 11-substituents as well. Besides methyl, also ethyl, ethynyl and propynyl were potent substituents. With ovulation inhibition tests, the ethyl, ethenyl and ethynyl substituents were the more potent compounds in all four series. However, compounds with methyl or ethynyl additions appeared to be glucocorticoidal in the hormone screening test irrespective of the 17-substituent, while with the three spiro series even methylene and ethenyl groups became active. Androgenicity was only observed at dose levels at or above 5 mg/kg, which is 2.5-fold weaker than ETG. Moreover, estrogenicity appeared negligible with the three spiro series, while with the 17alpha-ethynyl series methyl, ethyl, ethenyl and ethynyl substituents, a very high estrogenic potential was assessed. Based on the high efficacy and low side-effects, the following compounds show a high selectivity: 17alpha-ethynyl with ethyl, ethenyl and 2-propenyl substituents, six-membered spiromethylene ether with ethyl and six-membered-spiromethylene lactone with ethyl, 2-propenyl or 1-propynyl substituents. (ABSTRACT TRUNCATED)

Effects of cytochrome P450 inducers on 17alpha-ethinyloestradiol (EE2) conjugation by primary human hepatocytes

AIMS

Our objective was to elucidate further the underlying mechanism responsible for therapeutic failures observed with concomitant administration of the oral contraceptive 17alpha-ethinyloestradiol (EE2 ) and rifampicin.

METHODS

We investigated both oxidative and direct conjugative [3H]-EE2 metabolism by human liver S9 fraction and the effect of known enzyme-inducing drugs using a human hepatocyte induction model in vitro.

RESULTS

Cofactor dependent [3H]-EE2 metabolism by human liver S9 fraction produced 2-hydroxy-[3H]-EE2, 2-methoxy-[3H]-EE2, and direct [3H]-EE2 sulphate and glucuronide conjugates. Only two detectable metabolites of [3H]-EE2 were produced by the S9 fraction in the presence of all cofactors: [3H]-EE2-3-sulphate (75.7+/-7.6% s. d.) and 2-methoxy-3H-EE2 (2.6%+/-0.5% s.d.). Human hepatocytes extensively metabolized [3H]-EE2 to its glucuronide and sulphate conjugates. Small amounts of a 2-methoxy-[3H]-EE2 3-conjugate, < or = 10%, was observed but no. 2-hydroxy-[3H]-EE2 was detected. An unexpected finding in our study was increased [3H]-EE2-3-sulphate production (1.5-3.3 fold, n=3 donor livers) by hepatocytes pretreated with rifampicin compared to control hepatocytes. No statistically significant increase in [3H]-EE2-3-sulphation was observed in hepatocytes pretreated with 3-methylcholanthrene, phenobarbitone, dexamethasone, or omeprazole over nontreated hepatocytes. To our knowledge, this is the first observation of sulphotransferase induction by rifampicin in human hepatocytes in vitro resulting in increased [3H]-EE2 sulphation.

CONCLUSIONS

Our data indicate that the major EE2 metabolic products formed by human hepatocytes in vitro are direct EE2 conjugates with EE2 oxidation representing minor pathways. Further studies are required to establish the mechanism of sulphotransferase induction and the clinical relevance of our findings.

Transformation of a non-oestrogenic steroid metabolite to an oestrogenically active substance by minimal bacterial activity

The majority of oestrogenic material excreted from humans and wildlife, and therefore released into sewers, is in a conjugated form. However, the finding of "free" oestrogens in sewage effluent suggests that these metabolites are somehow converted back into an active form, before or during passage through a sewage treatment process. When male fathead minnows (Pimephales promelas) were continuously exposed to oestradiol-3-glucuronide, in a continuous-flow system, it demonstrated no inherent oestrogenic activity. However, when fish were exposed to effluent generated from laboratory simulations of sewage treatment processes, to which had been added oestradiol-3-glucuronide, oestrogenic activity was observed, suggesting microbial activity was capable of degrading the steroid metabolite into a more potent oestrogen. Oestrogenic potency was determined by measuring changes in plasma vitellogenin (egg yolk precursor) concentrations and gonadosomatic index. The results suggest that inactive metabolites of steroids are very readily biotransformed into biologically active oestrogens.

Effect of troglitazone on the pharmacokinetics of an oral contraceptive agent

Fifteen healthy women participated in a study to determine the effect of multiple doses of troglitazone on the pharmacokinetics of Ortho-Novum 1/35 (35 micrograms ethinyl estradiol [EE] and 1 mg norethindrone [NE]). Participants received three cycles (21 days each of active drug followed by 7 days without medication) of Ortho-Novum. During the third cycle, participants also received troglitazone 600 mg qd for 22 days. Pharmacokinetic profiles of EE and NE were determined on day 21 of the second and third cycles. Progesterone and sex hormone binding globulin (SHBG) levels were also measured. Troglitazone decreased EE Cmax and AUC(0-24) by 32% and 29%, respectively. Likewise, troglitazone decreased NE Cmax and AUC(0-24) by 31% and 30%, respectively. Plasma SHBG concentrations increased from 113 nmol/L during cycle 2 to 220 nmol/L during cycle 3. Troglitazone reduced plasma unbound AUC for NE by 49%. Serum progesterone levels were lower than 1.5 ng/mL on all occasions. Thus, coadministration of troglitazone and Ortho-Novum decreases the systemic exposure to EE and NE. A higher dose of oral contraceptive or an alternate method of contraception should be considered for patients treated with troglitazone.

Effect of ritonavir on the pharmacokinetics of ethinyl oestradiol in healthy female volunteers

AIMS

To assess the effects of the protease inhibitor ritonavir on the pharmacokinetics of ethinyl oestradiol in healthy female volunteers.

METHODS

This was an open-label, single centre study in 23 subjects who received two single doses of oral contraceptive containing 50 microg ethinyl oestradiol on Day 1 (alone) and on Day 29 during concomitant ritonavir. Each subject received 16 days of every 12 h doses of ritonavir from Day 15 through Day 30. Blood samples were collected for serum ethinyl oestradiol concentrations for 48 h after each dose and for plasma ritonavir on Day 29 at 0 and 4 h postdose.

RESULTS

Statistically significant decreases in ethinyl oestradiol mean Cmax (-32%) and mean AUC (-41%), and a statistically significant increase in the mean terminal elimination rate constant (+31%) were observed during concomitant ritonavir. The harmonic mean terminal half-life decreased from 17 h to 13 h during concomitant ritonavir. No statistically significant change was noted in tmax. The ratios of means (95% confidence intervals) for Cmax and AUC were 0.682 (0.612-0.758) and 0.595 (0.506-0.694), respectively. The changes in ethinyl oestradiol pharmacokinetics were consistent with an increase in clearance from enzymatic induction of glucuronidation and/or cytochrome P450 hydroxylation. Mean steady-state ritonavir concentrations of 6.5 and 13.4 microg ml(-1) were observed at 0 and 4 h postdose, respectively.

CONCLUSIONS

Considering the extent of the decrease in ethinyl oestradiol concentrations, the use of alternate contraceptive measures should be considered when ritonavir is being administered.

Comparative pharmacokinetics of two new steroidal estrogens and ethinylestradiol in postmenopausal women

It was the aim of the study to compare the pharmacokinetic properties of the two new estrogens, ZK 136295 and ZK 115194, with those of ethinylestradiol (EE2) after single intravenous (60 micrograms) and oral (120 and 240 micrograms) administration in 54 postmenopausal women. In particular, our objective was to examine whether one or both compounds were characterized by an improved oral bioavailability with less inter-subject variability than EE2. Drug serum concentrations were determined using specific radioimmunoassays for EE2 and ZK 136295, and a GC/MS/MS-method for ZK 115194. Following i.v. administration of the new estrogens and of EE2, the drugs were rapidly distributed in the body. The mean terminal half-lives were calculated to be 12.3 +/- 12.4, 28.7 +/- 9.6, and 26.1 +/- 11.1 h for ZK 136295, ZK 115194, and EE2 respectively. After oral administration of 120 micrograms, the absolute bioavailability was calculated to be about 40% for ZK 136295 as well as for EE2 with a high inter-individual variation (variation coefficient: 44 and 67%). By doubling the dose, the systemic availability increased dose-dependently for both drugs to about 70% with the same high inter-individual variation. Following single oral administration of 240 micrograms ZK 115194, the absolute bioavailability amounted to 33 +/- 19%. The present study clearly revealed that although the two new estrogens differed considerably in their pharmacokinetic behavior, they demonstrated a reduced and highly variable systemic availability similar to that of EE2.

Clinically significant drug interactions with cyclosporin. An update

Since its approval in 1983 for immunosuppressive therapy in patients undergoing organ and bone marrow transplants, cyclosporin has had a major impact on organ transplantation. It has significantly improved 1-year and 2-year graft survival rates, and decreased morbidity in kidney, liver, heart, heart-lung and pancreas transplantation. Several studies have supported the efficacy of cyclosporin in preventing graft-versus-host disease in bone marrow transplantation. Cyclosporin is also possibly effective in treating diseases of autoimmune origin and as an antineoplastic agent. The introduction of therapeutic drug monitoring of cyclosporin was extremely useful because of the wide inter- and intraindividual variability in the pharmacokinetics of cyclosporin after oral or intravenous administration. Optimal long term use of cyclosporin requires careful monitoring of the blood (or plasma) concentrations. Sustained and clinically significant drug-drug interactions can occur during long term therapy with cyclosporin. The coadministration of multiple drugs with cyclosporin could result in graft rejection, renal dysfunction or other undesirable effects. Any interaction that leads to modified cyclosporin concentrations is of potential clinical importance. Cyclosporin itself may have significant effects on the pharmacokinetics and/or pharmacodynamics of coadministered drugs, such as digoxin, HMG-CoA reductase inhibitors and antineoplastic drugs affected by multidrug resistance. Many drugs have been shown to affect the pharmacokinetics and/or pharmacodynamics of cyclosporin. Interactions between cyclosporin and danazol, diltiazem, erythromycin, fluconazole, itraconazole, ketoconazole, metoclopramide, nicardipine, verapamil, carbamazepine, phenobarbital (phenobarbitone), phenytoin, rifampicin (rifampin) and cotrimoxazole (trimethoprim/sulfamethoxazole) are well documented in a large number of patients. Other interactions (such as those with aciclovir, estradiol and imipenem) are documented only in isolated case studies.

Can grapefruit juice influence ethinylestradiol bioavailability?

The effects of grapefruit juice on the bioavailability of 17 alpha-ethinylestradiol (EE2) after a single oral administration of 50 micrograms EE2 have been investigated. The pharmacokinetics of EE2 were studied in an open, randomized, cross-over study in which 13 healthy volunteers were administered the drug with herbal tea or grapefruit juice (naringin, 887 mg/ml). In contrast to herbal tea, grapefruit juice increased the peak plasma concentration (Cmax) significantly to 137% (mean; range 64% to 214%, p = 0.0088) and increased the area under plasma concentration-time curve from 0 to 8 hours (AUC0-8) to 128% (mean; range 81% to 180%, p = 0.0186). This study shows that grapefruit juice increases the bioavailable amount of EE2. A possible explanation may be that grapefruit juice inhibits the metabolic degradation of EE2. Whether the increased bioavailability of EE2 following grapefruit juice administration is of clinical importance should be investigated in long-term studies.

Effects of felbamate on the pharmacokinetics of a low-dose combination oral contraceptive

The effects of felbamate on the pharmacokinetics of a low-dose combination oral contraceptive containing 30 micrograms ethinyl estradiol and 75 micrograms gestodene were assessed in a randomized, double-blind, placebo-controlled parallel-group study in healthy premenopausal female volunteers established in a regimen of oral contraceptive use. They received either placebo or 2400 mg/day felbamate from midcycle (day 15) to midcycle (day 14) of two consecutive oral contraceptive cycles (months 1 and 2). Pharmacokinetic assessments of ethinyl estradiol and gestodene were performed on day 14 of both cycles. To determine whether ovulation occurred, plasma progesterone and urinary luteinizing hormone levels were measured, and diaries recording vaginal bleeding were kept. Felbamate treatment resulted in a significant 42% decrease in gestodene area under the plasma concentration-time curve (0 to 24 hours) (p = 0.018) compared with baseline, whereas a minor but not clinically relevant effect was observed on the pharmacokinetic parameters of ethinyl estradiol. There were no changes in the pharmacokinetics of ethinyl estradiol or gestodene after placebo treatment. No volunteer showed hormonal evidence of ovulation; however, one volunteer reported the onset of intermenstrual bleeding during felbamate treatment. Because of the effect of felbamate on the pharmacokinetics of gestodene and the report of intermenstrual bleeding, it is possible that the contraceptive efficacy of low-dose combination oral contraceptives may be adversely affected during felbamate treatment.

Formation of ethinylestradiol in postmenopausal women during continuous treatment with a combination of estradiol, estriol and norethisterone acetate

Previous studies indicated that during treatment of postmenopausal women with preparations containing norethisterone, a small proportion of the progestogen is aromatized into ethinylestradiol. We therefore investigated the serum concentrations of estradiol, ethinylestradiol and norethisterone in 25 patients of a gynecological practice who were continuously treated for climacteric complaints with a combination of 2 mg estradiol, 1 mg estriol and 1 mg norethisterone acetate for a time period between 4 months and 6 years. Blood sampling occurred between 1 and 20 h after intake of the last tablet. The mean serum concentration of estradiol was 138 +/- 50 (53-279) pg/ml, of ethinylestradiol 18.1 +/- 13.5 (0-44) pg/ml, and of norethisterone 5.1 +/- 3.5 (0.7-11.6) ng/ml. The serum concentrations of estradiol showed a broad maximum between 1 and 14 h, and those of norethisterone a steep rise to maximum within 1-4 h after intake followed by a subsequent decline. Contrary to this, the ethinylestradiol levels were not related to the time after application indicating that the aromatization of norethisterone mainly occurs in peripheral tissue. There was no correlation between age, body mass index or duration of treatment and the ethinylestradiol levels. It is concluded that in the presence of the high estradiol concentrations the low conversion rate of norethisterone into ethinylestradiol is probably without clinical significance.

Pharmacokinetics of levonorgestrel and ethinylestradiol in 14 women during three months of treatment with a tri-step combination oral contraceptive: serum protein binding of levonorgestrel and influence of treatment on free and total testosterone levels in the serum

The pharmacokinetics of levonorgestrel (LNG) and ethinylestradiol (EE2) were determined in 14 healthy women (age 18 to 27 years) during a treatment period of three months with a tri-step combination oral contraceptive (Triquilar). Prior to this treatment period, the same women received a single administration of a coated tablet containing 0.125 mg LNG together with 0.03 mg EE2. There was a washout phase of one week between both treatments. Following single dose administration, a mean terminal half-life of 22 h was observed for LNG. The total clearance was 1.0 ml x min-1 x kg-1 and the volume of distribution was 128 l. During a treatment cycle, LNG levels in the serum accumulated by a factor of about four as compared to single dose administration. Steady-state drug levels were reached during the second half of each cycle. As compared to single dose administration, the following changes were observed for LNG at the end of treatment cycles one and three: reduced total (0.5 ml x min-1 x kg-1) and free clearance (50 ml x min-1 x kg-1) and a reduced volume of distribution (52 l). A concomitant increase in the SHBG concentrations by a factor of two as compared to pretreatment values was observed during treatment and appeared to be mainly responsible for the changes in the pharmacokinetics of LNG. Marked changes were also seen for the serum protein binding of LNG. After single dose administration, the free fraction of LNG was 1.4% and the fractions bound to SHBG and albumin were 55.0% and 43.6%, respectively. At the end of cycle one, the free fraction was only 1.0% and the fractions bound to SHBG and albumin were 69.4% and 30.0%, respectively. There was no difference in corresponding pharmacokinetic parameters and in the serum protein binding of LNG at the end of cycles one and three. On the last day of treatment cycles one and three, the AUC(0-4h) values of EE2 were 331.2 and 369.6 pg x ml-1 x h, respectively, which corresponds to an about 11-24% increase as compared to single dose administration, where an AUC(0-4h) value of 298.3 pg x ml-1 x h was found. Total and free testosterone concentrations decreased during treatment cycles one and three by about 41% and 55%, respectively, compared with the corresponding values measured prior to treatment.

Lansoprazole does not affect the bioavailability of oral contraceptives

The effects of the proton pump inhibitor lansoprazole on the bioavailability of a low-dose oral contraceptive (OC), containing 0.03 mg ethinyloestradiol (EE) and 0.15 mg levonorgestrel (LNG), were investigated. Twenty-four healthy females (aged 19-35 years; weight 60.6 +/- 7.1 kg) participated in a multiple-dose, placebo-controlled, randomized two-way cross-over study. All subjects received the OC over 2 full menstrual cycles from day 1 to day 21 separated by a drug-free interval of 7 days. Lansoprazole (60 mg day-1) or placebo was coadministered for 3 weeks each. Plasma concentrations of EE and LNG were determined by GC-MS. The 90% confidence intervals for ratios of Cmax and AUC after log transformation of both EE and LNG ranged between 91 and 111%, indicating that lansoprazole did not affect the bioavailability of EE and LNG.

Aromatization and hydrolysis of norethisterone-3-oxime in rabbit

Two pharmacologically active metabolites, norethisterone (NET) and ethinylestradiol (EE2), were detected by HPLC and HPLC-RIA methods in rabbit plasma following single i.v. and i.g. administration at a dose of 1 mg/20 microCi/kg of [3H]norethisterone-3-oxime (NETO). Approximately 48% (i.v. injection) and 91% (i.g. administration) of the NETO dose were hydrolyzed to NET. Although only 0.35% of the NETO dose was aromatized to EE2, due to its high estrogenic potency, EE2 might contribute to the overall pharmacological pattern of NETO in the rabbit.

New knowledge in the physiology of hormonal contraceptives

The present review addresses some of the new knowledge regarding the physiology and mechanisms of action of hormonal contraceptives. Specific topics that are discussed include oral contraceptives, intravaginal rings, long-term contraception, gonadotropin-releasing hormone agonists and antagonists, and antiprogestins. It has been shown that in combined oral contraceptives, lower doses of the new progestins (desogestrel, norgestimate, and gestodene) can be used to inhibit ovulation compared with norethindrone and levonorgestrel. In addition, lower doses of ethinyl estradiol are now used with progestins. Estrogen has been added to intravaginal rings containing levonorgestrel or norethindrone acetate to reduce frequency of bleeding. A new ring containing 3-keto-desogestrel is under evaluation. The use of subdermal implants containing levonorgestrel is currently a popular and highly effective method of long-term contraception. Studies show that gonadotropin-releasing hormone agonists and antagonists can provide ovarian suppression, and antiprogestins such as RU486 effectively block the midcycle gonadotropin surge. These and other novel methods of hormonal contraception are still years away from general use.

Individual variation in first-pass metabolism

Individual variation in pharmacokinetics has long been recognised. This variability is extremely pronounced in drugs that undergo extensive first-pass metabolism. Drug concentrations obtained from individuals given the same dose could range several-fold, even in young healthy volunteers. In addition to the liver, which is the major organ for drug and xenobiotic metabolism, the gut and the lung can contribute significantly to variability in first-pass metabolism. Unfortunately, the contributions of the latter 2 organs are difficult to quantify because conventional in vivo methods for quantifying first-pass metabolism are not sufficiently specific. Drugs that are mainly eliminated by phase II metabolism (e.g. estrogens and progestogens, morphine, etc.) undergo significant first-pass gut metabolism. This is because the gut is rich in conjugating enzymes. The role of the lung in first-pass metabolism is not clear, although it is quite avid in binding basic drugs such as lidocaine (lignocaine), propranolol, etc. Factors such as age, gender, disease states, enzyme induction and inhibition, genetic polymorphism and food effects have been implicated in causing variability in pharmacokinetics of drugs that undergo extensive first-pass metabolism. Of various factors considered, age and gender make the least evident contributions, whereas genetic polymorphism, enzymatic changes due to induction or inhibition, and the effects of food are major contributors to the variability in first-pass metabolism. These factors can easily cause several-fold variations. Polymorphic disposition of imipramine and propafenone, an increase in verapamil first-pass metabolism by rifampicin (rifampin), and the effects of food on propranolol, metoprolol and propafenone, are typical examples. Unfortunately, the contributions of these factors towards variability are unpredictable and tend to be drug-dependent. A change in steady-state clearance of a drug can sometimes be exacerbated when first-pass metabolism and systemic clearance of a drug are simultaneously altered. Therefore, an understanding of the source of variability is the key to the optimisation of therapy.

Single- and multiple-dose pharmacokinetics of a low-dose oral contraceptive in women with chronic renal failure undergoing peritoneal dialysis

OBJECTIVE

Our purpose was to compare the pharmacokinetic parameters of oral administration of a 35 micrograms ethinyl estradiol, 1 mg norethindrone pill in peritoneal dialysis patients and normal women.

STUDY DESIGN

A single-dose study was performed with five patients and four controls, followed by a multiple-dose study with five subjects in each group. Pharmacokinetic parameters were calculated by noncompartmental analysis and statistical analysis performed with Mann-Whitney U testing.

RESULTS

There is no difference in the pharmacokinetic parameters for norethindrone in peritoneal dialysis patients compared with normal women. During multiple dosing an increased area under the concentration curve and decreased apparent oral clearance was observed for ethinyl estradiol in peritoneal dialysis patients compared with normal women.

CONCLUSION

Peritoneal dialysis patients have decreased apparent oral clearance of ethinyl estradiol, leading to slightly higher serum concentrations compared with women with normal renal function. The clearance of norethindrone is the same in peritoneal dialysis patients and normal women.