The role of CYP2C and CYP3A in the disposition of 3-keto-desogestrel after administration of desogestrel

Pharmacokinetics, metabolism and serum concentrations of progestins used in contraception

Many different forms of hormonal contraception are used by millions of women worldwide. These contraceptives differ in the dose and type of synthetic progestogenic compound (progestin) used, as well as the route of administration and whether or not they contain estrogenic compounds. There is an increasing awareness that different forms of contraception and different progestins have different side-effect profiles, in particular their cardiovascular effects, effects on reproductive cancers and susceptibility to infectious diseases. There is a need to develop new methods to suit different needs and with minimal risks, especially in under-resourced areas. This requires a better understanding of the pharmacokinetics, metabolism, serum and tissue concentrations of progestins used in contraception as well as the biological activities of progestins and their metabolites via steroid receptors. Here we review the current knowledge on these topics and identify the research gaps. We show that there is a paucity of research on most of these topics for most progestins. We find that major impediments to clear conclusions on these topics include a lack of standardized methodologies, comparisons between non-parallel clinical studies and variability of data on serum concentrations between and within studies. The latter is most likely due, at least in part, to differences in intrinsic characteristics of participants. The review highlights the importance of insight on these topics in order to provide the best contraceptive options to women with minimal risks.

Discovery and Preclinical Development of Orally Active Small Molecules that Exhibit Highly Selective Follicle Stimulating Hormone Receptor Agonism

An orally active follicle stimulating hormone receptor allosteric agonist would provide a preferred treatment for over 16 million infertile women of reproductive age in low complexity methods (ovulation induction-intrauterine insemination) or in high complexity methods (controlled ovarian stimulation-in vitro fertilization). We present two oral follicle stimulating hormone receptor allosteric agonist compounds that have the desired pharmacology, drug metabolism, pharmacokinetics, and safety profile for clinical use. These molecules provide a single agent suitable for ovulation induction-intrauterine insemination or controlled ovarian stimulation-in vitro fertilization that is more convenient for patients and achieves similar preclinical efficacy as rec-hFSH. TOP5668, TOP5300 were evaluated in vitro in Chinese hamster ovary cells transfected with individual glycoprotein receptors measuring cAMP (FSHR, LH/CGR, thyroid stimulating hormone receptor). TOP5668 was found to have solely follicle stimulating hormone receptor allosteric agonist activity while TOP5300 was found to have mixed follicle stimulating hormone receptor allosteric agonist and LHR-AA activity. Both compounds stimulated concentration-dependent increases in estradiol production from cultured rat granulosa cells in the presence or absence of low dose rec-hFSH, while only TOP5300 stimulated testosterone production from rat primary Leydig cells. In pooled human granulosa cells obtained from patients undergoing controlled ovarian stimulation-in vitro fertilization, TOP5300 stimulated 7-fold greater maximal estradiol response than rec-hFSH and TOP5668 was 10-fold more potent than TOP5300. Both TOP5300 and TOP5668 stimulated follicular development in immature rat to the same efficacy as recombinant follicle stimulating hormone. In mice treated with TOP5300, in the presence of low dose of follicle stimulating hormone, there were no differences in oocyte number, fertilization rate, and hatched blastocyst rate in mice with TOP5300 and low dose follicle stimulating hormone vs. reference proteins pregnant mare serum gonadotropin or high dose rec-hFSH. ADME/PK and safety profiles were favorable. In addition, there was no appreciable activity on thyroid hormones by TOP5300 in 14-days toxicological study in rat or dog. The selected lead compound, TOP5300 stimulated a more robust increase in estradiol production from granulosa-lutein cells from women with polycystic ovarian syndrome patient compared to rec-hFSH. Conclusions: Two novel oral FSHR allosteric agonist, TOP5668 and TOP5300, were found to mimic the biological activity of rec hFSH in preclinical studies. Both compounds led to folliculogenesis and superovulation in rat and mice. Specifically, TOP5300 led to a similar number of ovulated oocytes that fertilized and developed into hatched blastocysts in mice when compared to rec-hFSH. The safety profile demonstrated lack of toxicity.

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.

The influence of bariatric surgery on oral drug bioavailability in patients with obesity: A systematic review

Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery. This review systematically examines the effects of bariatric surgery on drug pharmacokinetics, focusing especially on the mechanisms involved in restricting oral bioavailability. Studies with a longitudinal before-after design investigating the pharmacokinetics of at least one drug were reviewed. The need for dose adjustment following bariatric surgery was examined, as well as the potential for extrapolation to other drugs subjected to coinciding pharmacokinetic mechanisms. A total of 22 original articles and 32 different drugs were assessed. The majority of available data is based on Roux-en-Y gastric bypass (RYGBP) (18 of 22 studies), and hence, the overall interpretation is more or less limited to RYGBP. In the case of the majority of studied drugs, an increased absorption rate was observed early after RYGBP. The effect on systemic exposure allows for a low degree of extrapolation, including between drugs subjected to the same major metabolic and transporter pathways. On the basis of current understanding, predicting the pharmacokinetic change for a specific drug following RYGBP is challenging. Close monitoring of each individual drug is therefore recommended in the early postsurgical phase. Future studies should focus on the long-term effects of bariatric surgery on drug disposition, and they should also aim to disentangle the effects of the surgery itself and the subsequent weight loss.

Efavirenz decreases etonogestrel exposure: a pharmacokinetic evaluation of implantable contraception with antiretroviral therapy

OBJECTIVES

The primary objective of this study was to characterize the pharmacokinetics of etonogestrel (ENG) released from a contraceptive implant in Ugandan women living with HIV who were receiving efavirenz (EFV) or nevirapine (NVP)-based antiretroviral therapy (ART), compared with ART-naive women over 24 weeks.

DESIGN

Nonrandomized, parallel-group study with three arms: ART-naive, NVP, or EFV-based ART (N = 20/group).

METHODS

Sparse pharmacokinetic sampling of ENG, NVP, or EFV were performed at screening, entry, and then 1, 4, 12, and 24-week postimplant insertion. The primary endpoint was ENG concentrations at week 24, compared between the ART-naive group and each ART group, using geometric mean ratio (GMR) with 90% confidence intervals.

RESULTS

Sixty participants competed the 24-week study and data from 58 participants are included; one participant each was excluded from the NVP group and EFV group because of a sample processing error and ART nonadherence, respectively. At week 24, geometric mean ENG was 362, 341, and 66 pg/ml in the ART-naive, NVP, and EFV groups, respectively [GMR: NVP : ART-naive 0.94 (0.90-1.01); EFV : ART-naive 0.18 (0.17-0.20)]. NVP and EFV concentrations were lower at week 24 compared to preimplant [NVP: geometric mean 5.7 versus 6.8 mg/l, respectively, GMR 0.84 (0.83-0.85); EFV: geometric mean 3.6 versus 4.9 mg/l, respectively, GMR 0.73 (0.69-0.80)].

CONCLUSION

After 24 weeks of combined use, ENG exposure was 82% lower in women using EFV-based ART compared with ART-naive women. In contrast, NVP did not significantly impact ENG exposure. These results raise concerns about reduced effectiveness of implantable contraception for women taking EFV-based ART.

High Variability of Hormonal Levels and No Clinically Relevant Interaction Between Ethinyl Estradiol, Desogestrel and Lopinavir/Ritonavir in a Small Sample of HIV-positive Adolescents

BACKGROUND

We report the pharmacokinetic interactions of combined oral contraceptive (COC) containing ethinyl estradiol (EE2)/desogestrel (DSG) with lopinavir/ritonavir (LPV/r) in 16 HIV-positive adolescents.

METHODS

We measured Ctrough of EE2 and etonogestrel (ENG), the active metabolite of DSG, in HIV-positives on LPV/r-based ART; Ctrough of LPV/r with and without COC; endogenous progesterone. EE2/ENG levels were compared with our own historical data of HIV-negative controls.

RESULTS

Ctrough of EE2 and ENG varied from 3 to 57 pg/mL and from 1051 to 5000 pg/mL, respectively. The geometric mean ratios (GMR) of Ctrough in HIV-positives on LPV/r with COC versus HIV-negative controls with COC only were 0.68 (95% CI: 0.42 to 1.08) or 32% decreased (P = 0.10) for EE2; and 1.08 (95% CI: 0.73 to 1.60) or 8% increased (P = 0.68) for ENG. Endogenous progesterone was <1.0 ng/mL in all participants, consistent with anovulation. Ctrough of LPV decreased statistically insignificantly with COC and remained above the desired therapeutic minimum of 1.0 mg/L in all.

CONCLUSIONS

The study found no clinically relevant interaction between EE2/DSG and LPV/r. This was supported by suppressed ovulation, assessed by low endogenous progesterone levels in all participants; and preserved antiretroviral activity, assessed by LPV/r levels above the desired therapeutic minimum in all participants. However, the high variability of hormonal levels warrants individual monitoring and further investigation. Condom use should always be encouraged for infection prevention.

Drug-Drug Interactions, Effectiveness, and Safety of Hormonal Contraceptives in Women Living with HIV

Family planning options, including hormonal contraceptives, are essential for improving reproductive health among the more than 17 million women living with HIV worldwide. For these women, prevention of unintended pregnancy decreases maternal and child mortality, as well as reduces the risk of perinatal HIV transmission. Similarly, treatment of HIV with antiretroviral therapy (ART) is essential for reducing morbidity and mortality among HIV-positive individuals, as well as preventing HIV transmission between sexual partners or from mother to child. Importantly, despite the benefits of hormonal contraceptives, barriers to effective family planning methods exist for HIV-positive women. Specifically, drug-drug interactions can occur between some antiretroviral medications and some hormonal contraceptives, which may influence both contraceptive efficacy and tolerability. In addition, safety concerns have been raised about the impact of hormonal contraceptives on HIV disease progression, tolerability, and the risk of female-to-male HIV transmission. This review article summarizes the potential for drug-drug interactions, tolerability, and contraceptive effectiveness when hormonal contraceptives are combined with ART. In addition, the evidence surrounding the influence of hormonal contraceptives on HIV transmission and HIV disease progression in women living with HIV are summarized.

Contraceptive challenges in adolescents living with or at risk of HIV

Many adolescents living with or without HIV are sexually active and in need of continuous free access to a variety of contraceptive methods. Dual contraception, condom use together with reversible effective contraception (hormonal contraception [HC] or intrauterine device), seems to be the most effective option for female adolescents for protection from unintended pregnancy and sexually transmitted infections. When counselling on specific contraceptive choice, healthcare providers should be aware about possible interactions of some types of HC with the immune system, with possible changes in infectivity, as well as about drug interactions between mainly efavirenz and some types of progestins. Adding HC to HIV-positive status and antiretroviral therapy could have additive effects on metabolism. At the same time, the possible disadvantages of using HC in women living with HIV should be balanced against the advantages of very reliable methods of preventing unintended pregnancies. To reach and deliver a contraceptive service to more young women, it has proven effective to organise adolescent-friendly clinics and/or integrate them with HIV services. Diverse approaches, including community-based contraceptive service provision and the use of modern technologies, can complement the effort of providing contraceptive services to this target group of female adolescents living with HIV or at risk of HIV.

Effect of antiretroviral therapy including lopinavir/ritonavir or efavirenz on etonogestrel-releasing implant pharmacokinetics in HIV-positive women

OBJECTIVE

Data on the interaction between the etonogestrel (ENG) implant and antiretroviral therapy are lacking. We evaluated the effect of 2 highly active antiretroviral therapy (HAART) regimens (1 including efavirenz and the other ritonavir-boosted lopinavir) on the pharmacokinetic (PK) parameters of an ENG-releasing implant in HIV-positive women.

DESIGN

Prospective nonrandomized PK study.

METHODS

Forty-five HIV-positive women who desired to use ENG implants were included: 15 had received zidovudine/lamivudine + lopinavir/ritonavir for ≥3 months (LPV/r-based HAART group), 15 had received zidovudine/lamivudine + efavirenz for ≥3 months (EFV-based HAART group), and 15 had not received HAART (non-HAART group). PK parameters were measured using ultra-performance liquid chromatography-mass spectrometry at baseline and 2, 4, 6, 8, 10, 12, 16, 20, and 24 weeks after implant placement.

RESULTS

The EFV-based HAART regimen was associated with a reduction in the bioavailability of ENG, which showed decreases of 63.4%, 53.7%, and 70% in the area under the curve (AUC), maximum concentration (Cmax), and minimum concentration (Cmin) of ENG, respectively, compared with the non-HAART group. The LPV/r-based HAART regimen was associated with an increase in ENG bioavailability, which showed 52%, 60.6%, and 33.8% increases in the ENG AUC, Cmax, and Cmin, respectively, compared with the non-HAART group.

CONCLUSIONS

The coadministration of EFV decreased the bioavailability of ENG released from the implant, which could impair contraceptive efficacy. However, the coadministration of LPV/r increased the bioavailability of ENG released from the implant, which suggests that this antiretroviral combination does not impair the ENG implant efficacy.

Pharmacokinetics of the etonogestrel contraceptive implant in obese women

OBJECTIVE

We sought to examine the pharmacokinetics and acceptability of the etonogestrel contraceptive implant in obese women.

STUDY DESIGN

We developed and validated a plasma etonogestrel concentration assay and enrolled 13 obese (body mass index ≥30) women and 4 normal-weight (body mass index <25) women, who ensured comparability with historical controls. Etonogestrel concentrations were measured at 50-hour intervals through 300 hours postinsertion, then at 3 and 6 months to establish a pharmacokinetic curve.

RESULTS

All obese participants were African American, while all normal-weight participants were white. Across time, the plasma etonogestrel concentrations in obese women were lower than published values for normal-weight women and 31-63% lower than in the normal-weight study cohort, although these differences were not statistically significant. The implant device was found highly acceptable among obese women.

CONCLUSION

Obese women have lower plasma etonogestrel concentration than normal-weight women in the first 6 months after implant insertion. These findings should not be interpreted as decreased contraceptive effectiveness without additional considerations.

Probable Drug Interaction Between Warfarin and Hormonal Contraceptives

Objective:

To report a single patient case that presented with a probable drug interaction between warfarin and 3 methods of hormonal contraceptives, as assessed by the Horn Interaction Probability Scale.

Case Summary:

A 33-year-old female patient required long-term anticoagulation following an aortic valve replacement. While taking warfarin (38.5 mg weekly), she transitioned from a monophasic combined oral contraceptive (ethinyl estradiol plus norethindrone) to an implantable progestin-only contraceptive (etonogestrel) on the advice of her cardiologist. Nineteen days following etonogestrel implant insertion, her international normalized ratio (INR) decreased to 1.8 and required a 55.8% warfarin dose increase (resulting dose of 60 mg weekly). Within 10 months, the patient elected to have the implant removed due to vaginal bleeding. Nine days following removal of etonogestrel, she experienced a transient INR increase to 6.5. Her INR returned to within goal range after her warfarin dose was decreased to 55.5 mg weekly. After using barrier methods of contraception for 48 days, she initiated an oral progestin-only contraceptive (norethindrone). Further warfarin dose adjustments were made, resulting in a weekly warfarin dose of 53.5 mg. Thirty-nine days after initiation of oral norethindrone, she elected to discontinue use due to vaginal bleeding and no longer uses hormonal contraceptive methods. No further adjustments to her warfarin dose were warranted.

Discussion:

The increased warfarin requirement observed in this patient may have been a result of multiple factors. Based on a literature review, we hypothesize that the predominant mechanism of interaction was ethinyl estradiol inhibition of CYP1A2 and 2C19.

Conclusions:

We recommend that further in vivo studies be completed to definitively identify the mechanism of the interaction. It is necessary to intensify warfarin monitoring upon initiation or alteration of hormonal contraceptives.

Effect of etonogestrel contraceptive implant (Implanon) on portal blood flow and liver functions

BACKGROUND

This study was conducted to evaluate changes in portal blood flow and liver functions among women using Implanon for 2 years.

STUDY DESIGN

Fifty healthy Implanon users were enrolled in this longitudinal study and followed up for 24 months. Portal blood flow, assessed by color Doppler; prothrombin time and concentration; serum albumin; bilirubin; gamma-glutamyl transferase (GGT); alanine aminotransferase (ALT); and aspartate aminotransferase (AST) were measured before and 24 months after insertion.

RESULTS

After 24 months of Implanon insertion, there were no significant changes in portal blood flow, serum albumin, prothrombin time or concentration. However, there was a significant increase in serum levels of total and unconjugated bilirubin and GGT and a significant decrease in ALT and AST levels. All levels, however, remained within the normal range of values.

CONCLUSIONS

Implanon use for 2 years does not seem to influence portal hemodynamics. Changes in serum levels of bilirubin, GGT, ALT and AST are unlikely to be of clinical significance.

Drug-induced changes in P450 enzyme expression at the gene expression level: a new dimension to the analysis of drug-drug interactions

Drug-drug interactions (DDIs) caused by direct chemical inhibition of key drug-metabolizing cytochrome P450 enzymes by a co-administered drug have been well documented and well understood. However, many other well-documented DDIs cannot be so readily explained. Recent investigations into drug and other xenobiotic-mediated expression changes of P450 genes have broadened our understanding of drug metabolism and DDI. In order to gain additional information on DDI, we have integrated existing information on drugs that are substrates, inhibitors, or inducers of important drug-metabolizing P450s with new data on drug-mediated expression changes of the same set of cytochrome P450s from a large-scale microarray gene expression database of drug-treated rat tissues. Existing information on substrates and inhibitors has been updated and reorganized into drug-cytochrome P450 matrices in order to facilitate comparative analysis of new information on inducers and suppressors. When examined at the gene expression level, a total of 119 currently marketed drugs from 265 examined were found to be cytochrome P450 inducers, and 83 were found to be suppressors. The value of this new information is illustrated with a more detailed examination of the DDI between PPARalpha agonists and HMG-CoA reductase inhibitors. This paper proposes that the well-documented, but poorly understood, increase in incidence of rhabdomyolysis when a PPARalpha agonist is co-administered with a HMG-CoA reductase inhibitor is at least in part the result of PPARalpha-induced general suppression of drug metabolism enzymes in liver. The authors believe this type of information will provide insights to other poorly understood DDI questions and stimulate further laboratory and clinical investigations on xenobiotic-mediated induction and suppression of drug metabolism.