Interactions with oral contraceptives

The effect of hormonal contraceptive therapy on clinical laboratory parameters: a literature review

Hormonal contraceptives (HC) are widely used among women in reproductive ages. In this review, the effects of HCs on 91 routine chemistry tests, metabolic tests, and tests for liver function, hemostatic system, renal function, hormones, vitamins and minerals were evaluated. Test parameters were differently affected by the dosage, duration, composition of HCs and route of administration. Most studies concerned the effects of combined oral contraceptives (COC) on the metabolic, hemostatic and (sex) steroids test results. Although the majority of the effects were minor, a major increase was seen in angiotensinogen levels (90-375 %) and the concentrations of the binding proteins (SHBG [∼200 %], CBG [∼100 %], TBG [∼90 %], VDBP [∼30 %], and IGFBPs [∼40 %]). Also, there were significant changes in levels of their bound molecules (testosterone, T3, T4, cortisol, vitamin D, IGF1 and GH). Data about the effects of all kinds of HCs on all test results are limited and sometimes inconclusive due to the large variety in HC, administration routes and dosages. Still, it can be concluded that HC use in women mainly stimulates the liver production of binding proteins. All biochemical test results of women using HC should be assessed carefully and unexpected test results should be further evaluated for both methodological and pre-analytical reasons. As HCs change over time, future studies are needed to learn more about the effects of other types, routes and combinations of HCs on clinical chemistry tests.

Contraceptive use and counseling in patients with systemic lupus erythematosus

OBJECTIVES

(1) Describe contraception use in women with systemic lupus erythematosus (SLE); (2) characterize the types of contraception used by this population; (3) determine factors affecting the documentation of contraception use; (4) identify if contraception counseling was received in this population at risk for adverse pregnancy outcomes.

STUDY DESIGN

This cross-sectional study analyzed data from clinic visits from 2016 - 2018 among 453 women of reproductive age who have SLE. Documentation of contraception use, contraception method, contraception counseling, and other medication use were abstracted from the medical record and analyzed with percentage based statistics, chi-squared test, t-test, and logistic regression.

RESULTS

Of the 453 women included in the analysis, 71% had a method of contraception documented within 2 years of the study period. Only 37% were using highly effective contraception. 78% had documentation of contraception counseling. Half (50%) were using teratogenic medications; patients on teratogenic medications had higher odds of having a contraceptive method documented (OR 1.56, 95% CI 1.04 - 2.36) however 24% did not have any contraception documented. 28% of patients were using contraception for which they had a possible or absolute contraindication.

CONCLUSIONS

Given a substantial proportion of women with SLE did not have any contraception or contraceptive counseling documented, these findings suggest the need to improve universal reproductive health counseling in patients with SLE.

IMPLICATIONS

There is room to improve reproductive health care in patients with SLE through provider training to help optimize pregnancy outcomes in this high-risk population.

No. 329-Canadian Contraception Consensus Part 4 of 4 Chapter 9: Combined Hormonal Contraception

OBJECTIVE

To provide guidelines for health care providers on the use of contraceptive methods to prevent pregnancy and on the promotion of healthy sexuality.

OUTCOMES

Overall efficacy of cited contraceptive methods, assessing reduction in pregnancy rate, safety, and side effects; the effect of cited contraceptive methods on sexual health and general well-being; and the availability of cited contraceptive methods in Canada.

EVIDENCE

Medline and the Cochrane Database were searched for articles in English on subjects related to contraception, sexuality, and sexual health from January 1994 to December 2015 in order to update the Canadian Contraception Consensus published February-April 2004. Relevant Canadian government publications and position papers from appropriate health and family planning organizations were also reviewed.

VALUES

The quality of the evidence is rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care. Recommendations for practice are ranked according to the method described in this report.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Contraception in Patients with Rheumatic Disease

Contraception represents an important area of reproductive health for patients with rheumatic diseases given the potential pregnancy risks associated with active disease, teratogenic medications, and severe disease-related damage. A high proportion of patients with rheumatic disease do not use effective contraception. Long-acting contraceptives are most effective. Antiphospholipid-negative patients with stable systemic lupus erythematosus may use oral combined contraceptives. Antiphospholipid-positive patients, or patients with rheumatic disease with other risk factors for thrombosis, should avoid estrogen-containing contraceptives. Contraceptive methods should be addressed by both the rheumatologist and gynecologist to determine the safest, most effective, and most convenient form for each patient.

The other side of progestins: effects in the brain

Progestins are a broad class of progestational agents widely differing in their chemical structures and pharmacological properties. Despite emerging data suggest that progestins, besides their action as endometrial protection, can also have multiple nonreproductive functions, much remains to be discovered regarding the actions exerted by these molecules in the nervous system. Here, we report the role exerted by different progestins, currently used for contraception or in postmenopausal hormone replacement therapies, in regulating cognitive functions as well as social behavior and mood. We provide evidence that the effects and mechanisms underlying their actions are still confusing due to the use of different estrogens and progestins as well as different doses, duration of exposure, route of administration, baseline hormonal status and age of treated women. We also discuss the emerging issue concerning the relevant increase of these substances in the environment, able to deeply affect aquatic wildlife as well as to exert a possible influence in humans, which may be exposed to these compounds via contaminated drinking water and seafood. Finally, we report literature data showing the neurobiological action of progestins and in particular their importance during neurodegenerative events. This is extremely interesting, since some of the progestins currently used in clinical practice exert neuroprotective and anti-inflammatory effects in the nervous system, opening new promising opportunities for the use of these molecules as therapeutic agents for trauma and neurodegenerative disorders.

Progestogens used in postmenopausal hormone therapy: differences in their pharmacological properties, intracellular actions, and clinical effects

The safety of progestogens as a class has come under increased scrutiny after the publication of data from the Women's Health Initiative trial, particularly with respect to breast cancer and cardiovascular disease risk, despite the fact that only one progestogen, medroxyprogesterone acetate, was used in this study. Inconsistency in nomenclature has also caused confusion between synthetic progestogens, defined here by the term progestin, and natural progesterone. Although all progestogens by definition have progestational activity, they also have a divergent range of other properties that can translate to very different clinical effects. Endometrial protection is the primary reason for prescribing a progestogen concomitantly with postmenopausal estrogen therapy in women with a uterus, but several progestogens are known to have a range of other potentially beneficial effects, for example on the nervous and cardiovascular systems. Because women remain suspicious of the progestogen component of postmenopausal hormone therapy in the light of the Women's Health Initiative trial, practitioners should not ignore the potential benefits to their patients of some progestogens by considering them to be a single pharmacological class. There is a lack of understanding of the differences between progestins and progesterone and between individual progestins differing in their effects on the cardiovascular and nervous systems, the breast, and bone. This review elucidates the differences between the substantial number of individual progestogens employed in postmenopausal hormone therapy, including both progestins and progesterone. We conclude that these differences in chemical structure, metabolism, pharmacokinetics, affinity, potency, and efficacy via steroid receptors, intracellular action, and biological and clinical effects confirm the absence of a class effect of progestogens.

Effect of a Triphasic Oral Contraceptive on Drug-Metabolizing Enzyme Activity as Measured by the Validated Cooperstown 5+1 Cocktail

The effects of a common oral contraceptive preparation on the activity of 7 drug-metabolizing enzymes were investigated using the validated Cooperstown 5+1 Cocktail. In a randomized crossover fashion, 10 premenopausal women received caffeine, dextromethorphan, omeprazole, intravenous midazolam, and warfarin + vitamin K with and without a triphasic oral contraceptive (ethinyl estradiol 35 microg) and varying doses of daily norgestimate (0.18, 0.215, and 0.25 mg). Bioequivalence testing showed nonequivalence in drug versus no-drug treatment on the activity of drug-metabolizing enzymes (as reflected by metabolite ratios following probe drug administration); the activity of CYP1A2, CYP2C19, and NAT-2 decreased following the oral contraceptive, whereas the activity of CYP2C9 and CYP2D6 increased. No effects on xanthine oxidase or hepatic CYP3A were seen. Application of a non-parametric statistical testing approach revealed a significant difference only for CYP1A2 and CYP2C19. This triphasic oral contraceptive may have a clinically significant effect on the activity of some drug-metabolizing enzymes.

Concepts of contraception for adolescent and young adult women with chronic illness and disability

Sexual behavior is common in adolescents and young adults with or without chronic illness or disability, resulting in high levels of unplanned pregnancy and STDs. Individuals with chronic illness or disability should not receive suboptimal preventive health care. These individuals have a need for counseling regarding issues of sexuality and contraception. Sexually active adolescent and young adult women can be offered safe and effective contraception if they wish to avoid pregnancy. Women with chronic illnesses and disabilities who are sexually active should also be offered contraception based on their specific medical issues. Condoms are also recommended to reduce STD risks. Table 36 summarizes basic principles of contraception application for specific illnesses, which have been identified since the release of the combined OC in 1960. Clinicians should also consider the noncontraceptive benefits of this remarkable and life-changing technology that allows all reproductive age women to improve their lives, including those with chronic illnesses and disabilities.

Molecular mechanisms of steroid receptor-mediated actions by synthetic progestins used in HRT and contraception

Synthetic progestins are used by millions of women as contraceptives and in hormone replacement therapy (HRT), although their molecular mechanisms of action are not well understood. The importance of investigating these mechanisms, as compared to those of progesterone, has been highlighted by clinical evidence showing that medroxyprogesterone acetate (MPA), a first generation progestin, increases the risk of breast cancer and coronary heart disease in HRT users. A diverse range of later generation progestins with varying structures and pharmacological properties is available for therapeutic use and it is becoming clear that different progestins elicit beneficial and adverse effects to different extents. These differences in biological activity are likely to be due to many factors including variations in dose, metabolism, pharmacokinetics, bioavailability, and regulation of, and/or binding, to serum-binding proteins and steroidogenic enzymes. Since the intracellular effects on gene expression and cell signaling of steroids are mediated via intracellular steroid receptors, differential actions via the progesterone and other steroid receptors and their isoforms, are likely to be the major cause of differential intracellular actions of progestins. Since many progestins bind not only to the progesterone receptor, but also to the glucocorticoid, androgen, mineralocorticoid, and possibly the estrogen receptors, it is plausible that synthetic progestins exert therapeutic actions as well as side-effects via some of these receptors. Here we review the molecular mechanisms of intracellular actions of old (MPA, norethisterone, levonorgestrel, gestodene) vs. new (drospirenone, dienogest, trimegestone) generation progestins, via steroid receptors.

Pharmacology of different progestogens: the special case of drospirenone

The pharmacological properties of progestins used in contraception and hormone replacement therapy (HRT) vary, depending upon the molecules from which they are derived. Very small structural changes may induce considerable differences in effects. It is unclear if the currently available progestins are able to bind specifically to the progesterone receptors, PR-A or PR-B. The clinical relevance of more specific binding to one or the other isoforms of the progesterone receptor is still unknown. The development of new generations of progestins, with improved receptor-selectivity profiles, has been a great challenge. Steroidal and non-steroidal progesterone agonists have also been synthesized, although these molecules are at a very early stage of development. Several new progestins have been synthesized in the past decade, including dienogest, drospirenone, Nestorone, nomegestrol acetate and trimegestone. Drospirenone differs from the classic progestins in its derivation from spirolactone. The major effect of drospirenone is antimineralocorticoid activity. By that property, drospirenone causes decreased salt and water retention, and thus lowering of blood pressure. The affinity of drospirenone for the mineralocorticoid receptor is about five times that of aldosterone, the naturally occurring mineralocorticoid. In addition, drospirenone has no androgenic effect, but does exhibit partial antiandrogenic activity; its antiandrogenic potency is about 30% of that of cyproterone acetate, the progestin with the most potent antiandrogenic activity. This property, shared by several new progestins, may counteract the negative effect of androgens on hair growth, lipid changes, insulin and, possibly, body composition in postmenopausal women. Drospirenone has a long terminal half-life (about 32 hours), and its bioavailability is about 76%. Drospirenone, which has pharmacodynamic properties very similar to those of progesterone, has been developed as a combined oral contraceptive (30 microg ethinylestradiol/3 mg drospirenone; Yasmin, Schering AG, Berlin, Germany). Drospirenone is also available in combination with estradiol as an HRT preparation (1 mg 17beta-estradiol/2 mg drospirenone; Angeliq, Schering AG).

Anesthetic issues and anxiety management in the female oral and maxillofacial surgery patient

Gender differences in preoperative anxiety, perioperative pain experience, and physiologic responses to anesthesia exist. Pharmacokinetic and pharmacodynamic gender differences in anesthetic drugs are especially significant for propofol and nondepolarizing muscle relaxants. Nonobstetric anesthesia for the pregnant patient is briefly reviewed.

Therapy insight: guidelines for selection of contraception in women with rheumatic diseases

Use of contraceptives by women with rheumatic diseases, especially those with systemic lupus erythematosus, has long been thought to carry risks, such as disease exacerbation, thrombosis and other adverse effects. The use of effective contraception has, therefore, been avoided, despite many affected women being of reproductive age. Knowledge of risks and benefits of contraceptive methods in the general population has improved, as have the safety and effectiveness of hormonal contraceptives. Methods of administration have evolved and now include transdermal and intravaginal routes, a progesterone-releasing intrauterine device, and an extended-cycle oral contraceptive. Birth control pills are not all alike; the risk of adverse effects varies depending on the amount of estrogen and type of progestin used. Data show that patients with stable systemic lupus erythematosus are not at increased risk of disease flare while taking standard oral contraceptives. Despite a lack of randomized studies, evidence strongly suggests that the elevated risk of thrombosis makes estrogen-containing contraceptives unsuitable for patients with antiphospholipid antibody. Other important issues include potential interactions between hormonal contraceptives and other medications and possible risk of infection if an intrauterine device is used. Rheumatologists are increasingly working with gynecologists and patients to make choices about which contraceptive methods to use. Decisions should be individualized according to the patient's medical status, personal preference, and stage of reproductive life.

Tabac et fertilité chez la femme et l'homme

Cigarette smoking consequences on female and male reproduction have been evaluated for twenty years only and thus poorly spread in the general population. However, several studies have noticed noxious effects of tobacco before and after conception, in both women and men, from smokers gametes to their offspring. This negative impact occurs in spontaneous as well as in assisted reproduction (ART). For women, pregnancy rate is decreased, early spontaneous abortions are increased and ovarian reserve is altered. For men, standard sperm parameters are modified and spermatozoon nuclear quality is compromised. One of the mechanisms involved in those anomalies could be the oxidative stress produced by some cigarette smoking components. The consequences on smokers offspring are hardly evaluated yet: pathologies of the respiratory system, decrease of fecundity and cancers outcomes. In conclusion, it seems obvious that smokers - men as women - have to quit smoking before having a parental project.

[Update on contraception]

Since the introduction of hormonal contraceptives in the 1960s, great advances have been achieved in contraception. Biological effects of sexual steroids as well as risks and benefits of oral contraception are better estimated. After the development of a new hormone-containing intra-uterine system, new hormone delivery systems offer women safe and effective contraceptive options. These new options that combine high efficacy and ease of use should allow better acceptance and compliance than daily pill ingestion and should then reduce the high rate of unintended pregnancies terminated by elective abortion. Transdermal contraceptive system and vaginal ring offer a promising innovative approach in pregnancy prevention. Subdermal implants give women the choice of a highly effective contraceptive system in spite of significant side effects. New hormonal delivery systems such as injectables are under development. Hysteroscopic tubal sterilization is now also available and is a very effective procedure. This wide variety of new contraceptive methods offers a marked improvement from previous medications for users by providing better efficacy and tolerability.

Short-term oral contraceptive use and the risk of epithelial ovarian cancer

Oral contraceptive (OC) use has been consistently linked to a reduction in ovarian cancer in a dose-dependent fashion. Whether short-term OC use is protective remains controversial. In 1994-1998 in the Delaware Valley of Pennsylvania, the authors examined the association between short-term OC use and ovarian cancer in a population-based case-control study comparing 608 incident epithelial ovarian cancer cases with 926 community controls. Using unconditional logistic regression and adjusting for known confounders, they found a significant reduction in ovarian cancer risk for women who had used OCs for < or =6 months (odds ratio = 0.73, 95% confidence interval: 0.54, 0.99). This protective effect was observed in only that group who had used OCs for < or =6 months and stopped because of side effects (odds ratio = 0.59, 95% confidence interval: 0.40, 0.87 for side effects and odds ratio = 0.91, 95% confidence interval: 0.60, 1.37 for non-side-effects). Women who used OCs for >6 months were at a reduced risk independent of their reason for stopping. Results were similar when stratifying by parity and hormone therapy use. Thus, OC use for as little as 6 months provides significant protection against ovarian cancer risk, protection that appears limited to those women who stop using OCs because of side effects. Mediating factors may reflect endogenous hormone levels, OC metabolism, or OC bioactivity.

Ursodeoxycholic acid does not affect ethinylestradiol bioavailability in women taking oral contraceptives

OBJECTIVE

Contraception is recommended for female patients during ursodeoxycholic acid (UDCA) treatment for the potential teratogenic effect of this bile acid, and the aim of our study was to determine whether this treatment affects the bioavailability of ethinylestradiol (EE2).

METHODS

In this double-blind, randomised study, we measured EE2 pharmacokinetics in eight healthy volunteers randomly allocated to receive oral contraceptive (30 microg EE2 and 75 microg gestodene) plus either UDCA (8-10 mg/kg per day) or placebo for 21 days during the first of three consecutive menstrual cycles. After a washout period during the second cycle, the subjects received the alternative treatment during the third menstrual cycle. Serum EE2 and UDCA were measured using radioimmunoassay and gas chromatography-mass spectrometry, respectively.

RESULTS

The profile for serum EE2 concentration was similar during UDCA (mean maximum serum concentration 177 pg/ml, SEM 59) and during placebo treatment (153 pg/ml, SEM 62), and mean area under the curve (AUC) was 1374 pg/h per ml (SEM 580) and 1320 pg/h per ml (SEM 551) during the two regimens, respectively. The point estimates and 90% confidence intervals of UDCA/placebo ratios for EE2 AUC and for maximum serum concentration were 1.1 (0.8-1.5) and 1.2 (1.0-1.4), respectively. Mean serum triglycerides concentration increased from 58.3 mg/dl (SEM 6.8) at enrolment to 91.4 mg/dl (SEM 10.7) during placebo (P < 0.01) and to 88.6 mg/dl (SEM 13.7) during UDCA treatment (P < 0.05). During UDCA treatment, serum enrichment with this bile acid and with the metabolite iso-UDCA was 29% (16%) and 3% (2%), respectively.

CONCLUSION

Co-administration with UDCA does not affect the bioavailability of EE2 in healthy volunteers, indicating that contraceptive efficacy is not affected.

Oral contraceptive efficacy and antibiotic interaction: a myth debunked

The purpose of this study was to review the pharmacokinetic and clinical literature regarding the efficacy of oral contraceptives when used concomitantly with antibiotic therapy. Relevant literature was identified by searching MEDLINE and EMBASE. Other sources were located by consulting the bibliographies of the material collected from MEDLINE and EMBASE. Pharmacokinetic evidence demonstrates that plasma levels of oral contraceptive steroids are unchanged with the concomitant administration of antibiotics, including ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline. However, reduced steroid levels have been reported in women taking rifampin with oral contraceptives. Clinical reports of contraceptive failure with antibiotic use are retrospective, have multiple potential biases, and are not supported by pharmacokinetic data. Available scientific and pharmacokinetic data do not support the hypothesis that antibiotics (with the exception of rifampin) lower the contraceptive efficacy of oral contraceptives.

Effects of ABT-761, a novel 5-lipoxygenase inhibitor, on the pharmacokinetics of a single dose of ethinyl estradiol and levonorgestrel in healthy female volunteers

ABT-761 is a second-generation 5-lipoxygenase inhibitor in clinical development for the treatment of asthma. The effects of ABT-761 on the pharmacokinetics of an oral contraceptive were assessed in 21 female adult volunteers in a phase I, multiple-dose, open-label study. Subjects received a single dose of oral contraceptive (30 microg ethinyl estradiol and 0.15 mg of levonorgestrel) on each of days 1 and 29. Oral doses of 300 mg of ABT-761 were administered once daily beginning on day 15 continuing through day 29. Statistically significant decreases in maximum concentration (Cmax) and area under the concentration-time curve (AUC) of ethinyl estradiol were observed when oral contraceptive was administered concomitantly with ABT-761 compared with administration of oral contraceptive alone. The mean elimination rate constant of ethinyl estradiol increased by 30% (a mean decrease of 3.8 hours in half-life), and the mean apparent volume of distribution during the terminal phase (Vd(beta)/F) of ethinyl estradiol increased by 73% in the presence of ABT-761. Mean Cmax and AUC values for norgestrel decreased by 12% and 10%, respectively, when administered with ABT-761. Mean values for time to Cmax (tmax), terminal rate constant (beta), half-life (t1/2), and Vd(beta)/F of norgestrel were similar when oral contraceptive was administered alone or concomitantly with ABT-761. The mechanism responsible for the effect of ABT-761 on the clearance of ethinyl estradiol remains undefined. Because results of previous multiple-dose studies of ABT-761 do not provide any evidence of autoinduction, the effects of ABT-761 on the pharmacokinetics of ethinyl estradiol are more likely related to absorption of ethinyl estradiol.

Drug interactions of macrolides: emphasis on dirithromycin

OBJECTIVE

To describe the drug interactions of dirithromycin, a new macrolide, and to compare them with those of other macrolides.

DATA SOURCES

A literature search was performed using MEDLINE to identify articles published between January 1980 and July 1995 concerning the drug interactions of macrolides. Published abstracts were also examined. All studies using dirithromycin were performed under the sponsorship of Eli Lilly and Company.

DATA SYNTHESIS

Erythromycin, the first macrolide discovered, is metabolized by the cytochrome P450 enzyme system. By decreasing their metabolism, erythromycin can interact with other drugs metabolized by the cytochrome P450 enzymes. The lack of such interactions would be a desirable feature in a newer macrolide. We describe studies performed to detect any interactions of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, and ethinyl estradiol. The studies showed that dirithromycin, like azithromycin, is much less likely to cause the interactions detected with clarithromycin and erythromycin. A review of the literature showed differences among macrolides in their abilities to inhibit cytochrome P450 enzymes and, thus, to cause drug-drug interactions. Erythromycin and clarithromycin inhibit cytochrome P450 enzymes, and have been implicated in clinically significant interactions. Azithromycin and dirithromycin neither inhibit cytochrome P450 enzymes nor are implicated in clinically significant drug-drug interactions.

CONCLUSIONS

Dirithromycin, a new macrolide, does not inhibit the cytochrome P450 enzyme system. The concomitant use of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, or ethinyl estradiol was studied in pharmacokinetic and pharmacodynamic studies. In vitro, dirithromycin did not bind cytochrome P450. In healthy subjects, erythromycin increases the clearance of cyclosporine by 51%, whereas dirithromycin causes no significant changes in the pharmacokinetics of cyclosporine. In kidney transplant recipients, administration of dirithromycin was associated with a significant (p < 0.003) decrease of 17.4% in the clearance of cyclosporine. In patients taking low-dose estradiol, the administration of dirithromycin caused a significant (p < 0.03) increase of 9.9% in the clearance of ethinyl estradiol; escape ovulation did not occur. Unlike erythromycin and clarithromycin, dirithromycin had no significant effects on the pharmacokinetics of theophylline, terfenadine, or warfarin. The alterations typical of drug interactions that are based on inhibition of the cytochrome P450 system occurring with erythromycin and clarithromycin were not observed with dirithromycin.

Bioavailability of orally administered sex steroids used in oral contraception and hormone replacement therapy

The concept of bioavailability is discussed with particular references to the sex steroids. Problems encountered in the measurement of bioavailability of these steroids and the various factors that may affect their bioavailability are briefly described. Information regarding the bioavailability of the estrogens and gestogens, some of which are prodrugs, used in oral contraception and hormone replacement therapy is summarized and the implications regarding the clinical use of these steroids are discussed.

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.

Pharmacokinetic and pharmacologic variation between different estrogen products

Due to the complex nature of endogenous and exogenous hormone concentration, formation, and metabolism and assay complexity, the pharmacokinetics of estrogen are difficult to study. Oral estrogens have minimal systemic bioavailability (2% to 10%) due to gut and liver (first-pass) metabolism. High concentrations of estrone are achieved with oral administration, whereas higher concentrations of estradiol are generally achieved after percutaneous absorption. Although vaginal products (such as gel, rings, etc.) are administered locally, they achieve high serum concentrations. Estradiol and estrone concentrations and estradiol-to-estrone ratios vary with different estrogen therapies. Approximately 95% to 98% of estradiol is bound loosely to albumin or tightly to sex hormone binding globulin, the major binding protein. The terminal half lives for the different estrogen compounds (after oral or intravenous administration) vary from 1-12 hours. Some conversion rates have been calculated between estrogen and its metabolites. Smoking decreases achievable estrogen concentrations, and has a greater effect on oral products. Oral contraceptives have been found to decrease antipyrine clearance. In the one study evaluating conjugated estrogens, antipyrine clearance was not altered. Oral contraceptives have a variable effect on the elimination of medications. Acetaminophen clearance is increased, whereas clearance of some benzodiazepines, caffeine,and prednisolone is decreased. Phenytoin increases the metabolism of conjugated estrogens. The various estrogen products may produce different clinical effects based on composition. The metabolites (minor components) of conjugated estrogens have been found to have significant effects on lipid concentrations, uterine weight, liver generated compounds, and bone resorption. Because transdermal products bypass the first-pass effect, delayed or decreased effects on lipid profiles and liver generated compounds have been observed.

Bioequivalence requirements for generic products

Many countries have established procedures for the introduction of generic pharmaceutical products. In order to protect consumers, these generic products must be demonstrated to be therapeutically equivalent to a previously approved product, typically an innovator product. The therapeutic equivalence of a generic and an innovator product is most commonly based on the demonstration of bioequivalence, i.e. clinically insignificant differences in the rate and extent of drug absorption usually assessed from pharmacokinetic measurements. This article reviews the bioequivalence requirements for generic products and, in the interest of promoting international harmonisation, highlights those areas where differences exist among countries.

New progestogens in oral contraception

The major developments in combined oral contraceptives (COCs) have been a reduction in the total dose of both the oestrogen and progestogen administered per cycle and the introduction of new progestogens which are claimed to be more 'selective' than the older ones. This review examines in detail the clinical efficacy of the new COCs, where possible in comparison with those containing levonorgestrel or norethisterone, and their pharmacological effect on carbohydrate and lipid metabolism, haematological factors, pituitary-ovarian function and serum protein and androgen concentrations. Based mainly on the pharmacological evidence, the newer COCs are an improvement over the older low-dose formulations and are clearly preferable to the high-dose ones. However, the older low-dose COCs, despite many years of use, have not resulted in a high incidence of adverse effects. The increasing use of the new COCs, as evidenced by their increasing market share throughout Europe, does indicate that they have been well accepted in clinical practice.

Common food additives are potent inhibitors of human liver 17 alpha-ethinyloestradiol and dopamine sulphotransferases

Interactions between dietary xenobiotics, drugs and biologically active endogenous compounds are a potential source of idiosyncratic adverse pathology. We have examined the inhibition of the sulphation of a number of xenobiotics and endobiotics in human liver cytosol by 15 food additives and constituents. Sulphation of dehydroepiandrosterone was resistant to inhibition by all compounds tested; however, dopamine sulphotransferase (ST) activity was inhibited strongly by (+/-)-catechin, (+)-catechin, octyl gallate, tartrazine and vanillin. Sulphation of the xenobiotic steroid 17 alpha-ethinyloestradiol (EE2) was inhibited by vanillin, erythrosin B and octyl gallate. Of these compounds, only vanillin was found to be sulphated to a significant extent by both human liver and platelets, and vanillin was determined to be a substrate for the monoamine-sulphating isoenzyme of phenolsulphotransferase. Vanillin was found to inhibit 50% of liver EE2 ST activity (IC50) at a concentration of approximately 1.3 microM and the mode of inhibition was non-competitive. The implications of these results for the adverse side effects associated with food additives and oral contraceptives are discussed.