Oral contraception does not alter single dose saquinavir pharmacokinetics in women

From hazard to risk prioritization: a case study to predict drug-induced cholestasis using physiologically based kinetic modeling

Cholestasis is characterized by hepatic accumulation of bile acids. Clinical manifestation of cholestasis only occurs in a small proportion of exposed individuals. The present study aims to develop a new approach methodology (NAM) to predict drug-induced cholestasis as a result of drug-induced hepatic bile acid efflux inhibition and the resulting bile acid accumulation. To this end, hepatic concentrations of a panel of drugs were predicted by a generic physiologically based kinetic (PBK) drug model. Their effects on hepatic bile acid efflux were incorporated in a PBK model for bile acids. The predicted bile acid accumulation was used as a measure for a drug's cholestatic potency. The selected drugs were known to inhibit hepatic bile acid efflux in an assay with primary suspension-cultured hepatocytes and classified as common, rare, or no for cholestasis incidence. Common cholestasis drugs included were atorvastatin, chlorpromazine, cyclosporine, glimepiride, ketoconazole, and ritonavir. The cholestasis incidence of the drugs appeared not to be adequately predicted by their Ki for inhibition of hepatic bile acid efflux, but rather by the AUC of the PBK model predicted internal hepatic drug concentration at therapeutic dose level above this Ki. People with slower drug clearance, a larger bile acid pool, reduced bile salt export pump (BSEP) abundance, or given higher than therapeutic dose levels were predicted to be at higher risk to develop drug-induced cholestasis. The results provide a proof-of-principle of using a PBK-based NAM for cholestasis risk prioritization as a result of transporter inhibition and identification of individual risk factors.

Sexual life and contraception in people living with HIV

As people living with HIV (PLH) are living longer and healthier lives in the era of highly active antiretroviral therapy, common reproductive health issues are becoming more important. According to WHO, PLH should be offered routine counselling on sexual and reproductive health, so that they can implement informed, healthy, and appropriate decisions. PLH need special attention with regard to the use of contraceptive methods that provide dual protection against HIV/sexually transmitted infection transmission and unintended pregnancies. This article includes literature review on sexual life and contraception in the context of HIV infection including barrier methods, natural methods, sterilization, hormonal contraception, intrauterine device, spermicides/ microbicides and emergency contraception. To date, there is no perfect method that provides both protection against HIV transmission and unintended pregnancy. Although male condom remains the principal contraceptive method, its male-controlled usage is its most important obstacle. This article describes the pros and cons of each method for PLH as well as the interaction between hormonal contraceptives and antiretroviral drugs. Many questions remain to be answered. It is therefore important that studies of different methods of contraception in PLH continue.

Drug interactions between hormonal contraceptives and antiretrovirals

OBJECTIVE

To summarize published evidence on drug interactions between hormonal contraceptives and antiretrovirals.

DESIGN

Systematic review of the published literature.

METHODS

We searched PubMed, POPLINE, and EMBASE for peer-reviewed publications of studies (in any language) from inception to 21 September 2015. We included studies of women using hormonal contraceptives and antiretrovirals concurrently. Outcomes of interest were effectiveness of either therapy, toxicity, or pharmacokinetics. We used standard abstraction forms to summarize and assess strengths and weaknesses.

RESULTS

Fifty reports from 46 studies were included. Most antiretrovirals whether used for therapy or prevention, have limited interactions with hormonal contraceptive methods, with the exception of efavirenz. Although depot medroxyprogesterone acetate is not affected, limited data on implants and combined oral contraceptive pills suggest that efavirenz-containing combination antiretroviral therapy may compromise contraceptive effectiveness of these methods. However, implants remain very effective despite such drug interactions. Antiretroviral plasma concentrations and effectiveness are generally not affected by hormonal contraceptives.

CONCLUSION

Women taking antiretrovirals, for treatment or prevention, should not be denied access to the full range of hormonal contraceptive options, but should be counseled on the expected rates of unplanned pregnancy associated with all contraceptive methods, in order to make their own informed choices.

Effects of resveratrol on P-glycoprotein and cytochrome P450 3A in vitro and on pharmacokinetics of oral saquinavir in rats

Background

The intestinal cytochrome P450 3A (CYP 3A) and P-glycoprotein (P-gp) present a barrier to the oral absorption of saquinavir (SQV). Resveratrol (RESV) has been indicated to have modulatory effects on P-gp and CYP 3A. Therefore, this study was to investigate the effects of RESV on P-gp and CYP 3A activities in vitro and in vivo on oral SQV pharmacokinetics in rats.

Methods

In vitro, intestinal microsomes were used to evaluate RESV effect on CYP 3A-mediated metabolism of SQV; MDR1-expressing Madin–Darby canine kidney (MDCKII-MDR1) cells were employed to assess the impact of RESV on P-gp-mediated efflux of SQV. In vivo effects were studied using 10 rats randomly assigned to receive oral SQV (30 mg/kg) with or without RESV (20 mg/kg). Serial blood samples were obtained over the following 24 h. Concentrations of SQV in samples were ascertained using high-performance liquid chromatography-tandem mass spectrometry analysis.

Results

RESV (1–100 μM) enhanced residual SQV (% of control) in a dose-dependent manner after incubation with intestinal microsomes. RESV (1–100 μM) reduced the accumulation of SQV in MDCKII-MDR1 cells in a concentration-dependent manner. A double peaking phenomenon was observed in the plasma SQV profiles in rats. The first peak of plasma SQV concentration was increased, but the second peak was reduced by coadministration with RESV. The mean AUC_0–∞ of SQV was slightly decreased, with no statistical significance probably due to the high individual variation.

Conclusion

RESV can alter the plasma SQV concentration profiles, shorten the T_max of SQV. RESV might also cause a slight decrease tendency in the SQV bioavailability in rats.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

Hormonal contraceptive use in HIV-infected women using antiretroviral therapy: A Systematic review

BACKGROUND

While extensive research has explored pharmacokinetic interactions between antiretroviral therapy and hormonal contraception, few studies have examined whether these interactions affect clinical outcomes. To address this gap, we conducted a systematic review of the literature that describes hormonal contraceptive among HIV infected women who also antiretroviral therapy, focusing on papers that address clinically important outcomes such as pregnancy or ovulation.

METHODS

An electronic literature search was conducted of PUBMED and OVID to identify all articles that addressed hormonal contraception co-administered with antiretroviral therapy published in English between 01 January 1990 and 30 October 2014. In addition, manual reference checks of all articles of interest were conducted to identify articles not captured in the electronic search. Our search criteria identified 405 records. The title and abstract of data reports retrieved via the search were reviewed to identify potential articles of interest. Those with any indication of the main outcomes of interest were considered for inclusion (N=162). Abstracts were then reviewed to identify those manuscripts that would merit a review of the full text version (N=64). Eight articles that addressed the outcomes of interest were identified. The Newcastle-Ottawa Scale was used to assess the quality of these articles.

RESULTS

The studies reviewed were limited in a number of ways that precluded their providing a rigorous assessment of the efficacy of contraception when co-administered with antiretroviral therapy.

DISCUSSION

None of the studies were of adequate quality to provide the guidance that providers and HIV infected women need when considering contraceptive options. High quality, well-powered studies are required to address the efficacy of hormonal contraception when co-administered with antiretroviral therapy.

Effects of hormonal contraception on antiretroviral drug metabolism, pharmacokinetics and pharmacodynamics

Among women, human immunodeficiency virus type 1 (HIV-1) infection is most prevalent in those of reproductive age. These women are also at risk of unintended or mistimed pregnancies. Hormonal contraceptives (HCs) are one of the most commonly used methods of family planning worldwide. Therefore, concurrent use of HC among women on antiretroviral medications (ARVs) is increasingly common. ARVs are being investigated and have been approved for pre-exposure prophylaxis (PrEP), and therefore, drug-drug interactions must also be considered in HIV-1-negative women who want to prevent both unintended pregnancy and HIV-1 infection. This article will review four main interactions: (i) the effect of HCs on ARV pharmacokinetics (PK) and pharmacodynamics (PD) during therapy, (ii) the effect of ARVs on HC PK and PD, (iii) the role of drug transporters on drug-drug interactions, and (iv) ongoing research into the effect of HCs on pre-exposure prophylaxis PK and PD.

Drug interactions between antiretrovirals and hormonal contraceptives

INTRODUCTION

Significant advances in antiretroviral therapy have transformed HIV into a chronic manageable disease, and millions of women living with HIV now have the opportunity to reconsider their reproductive choices, be it contraception or pregnancy planning. Hormonal contraceptives are metabolized by cytochrome P450 isoenzymes and sulfate and glucuronide conjugation in the liver. Many antiretrovirals have inducing or inhibiting effects on the cytochrome P450 system. As such, the pharmacokinetics of hormonal contraceptives can be affected by antiretroviral therapy with potential for significant clinical impact.

AREAS COVERED

This article presents the pharmacology and metabolism of selected antiretrovirals and hormonal contraceptives, and highlights the potential interactions between these two classes of drugs. Furthermore, the authors present the pharmacokinetic evidence of interactions from available clinical trials, product monographs, and international conference abstracts.

EXPERT OPINION

Drugs most likely to interact with combined oral contraceptives, transdermal and implant contraceptives include protease inhibitors, the NNRTIs efavirenz and nevirapine, and cobicistat-boosted elvitegravir. There do not appear to be significant pharmacokinetic interactions with depo-medroxyprogesterone or intrauterine systems and antiretrovirals, although further study is needed. Clinicians working with HIV-positive women need to know the significance of these interactions in order to properly counsel patients and prevent unplanned pregnancies.

Contraception for the HIV-positive woman: a review of interactions between hormonal contraception and antiretroviral therapy

BACKGROUND

Preventing unintended pregnancy in HIV-positive women can significantly reduce maternal-to-child HIV transmission as well as improve the woman's overall health. Hormonal contraceptives are safe and effective means to avoid unintended pregnancy, but there is concern that coadministration of antiretroviral drugs may alter contraceptive efficacy.

MATERIALS AND METHODS

We performed a literature search of PubMed and Ovid databases of articles published between January 1980 and February 2012 to identify English-language reports of drug-drug interactions between hormonal contraceptives (HCs) and antiretroviral drugs (ARVs). We also reviewed the FDA prescribing information of contraceptive hormone preparations and antiretrovirals for additional data and recommendations.

RESULTS

Twenty peer-reviewed publications and 42 pharmaceutical package labels were reviewed. Several studies of combined oral contraceptive pills (COCs) identified decreased serum estrogen and progestin levels when coadministered with certain ARVs. The contraceptive efficacy of injectable depot medroxyprogesterone acetate (DMPA) and the levonorgestrel intrauterine system (LNG-IUS) were largely unaffected by ARVs, while data on the contraceptive patch, ring, and implant were lacking.

CONCLUSIONS

HIV-positive women should be offered a full range of hormonal contraceptive options, with conscientious counseling about possible reduced efficacy of COCs and the contraceptive implant when taken with ARVs. DMPA and the LNG-IUS maintain their contraceptive efficacy when taken with ARVs.

[Evidence-based therapeutic drug monitoring for saquinavir]

The human immunodeficiency virus (HIV) protease inhibitor saquinavir displays a large inter-individual variability in its pharmacokinetic parameters, related to a low absorption rate and an important hepatic metabolism. Based on literature, is the saquinavir therapeutic drug monitoring relevant? In naïve HIV-infected patients, the probability of achieving an undetectable HIV viral load at W48 was significantly associated with a saquinavir plasma trough concentration >100 ng/mL. Two studies in HIV-infected pre-treated patients reported that the genotypic inhibitory quotient was a predictive factor of virologic response with a threshold value around 40 ng/mL/mutation. Concerning the exposure-toxicity relationship, the risk of occurrence of grade 3-4 abdominal pains was more frequently associated with high concentrations of saquinavir, but without threshold value determination. Several studies, one of which was randomized, have reported the interest of saquinavir therapeutic drug monitoring to optimize the virologic response. Therefore, the level of evidence of the interest of saquinavir therapeutic drug monitoring is "recommended".

Contraception in HIV-positive female adolescents

Sexual behavior of HIV-positive youths, whether infected perinatally, through risky behavior or other ways, is not substantially different from that of HIV-uninfected peers. Because of highly active antiretroviral therapy, increasing number of children, infected perinatally, are surviving into adolescence and are becoming sexually active and need reproductive health services. The objective of this article is to review the methods of contraception appropriate for HIV-positive adolescents with a special focus on hormonal contraceptives. Delaying the start of sexual life and the use of two methods thereafter, one of which is the male condom and the other a highly effective contraceptive method such as hormonal contraception or an intrauterine device, is currently the most effective option for those who desire simultaneous protection from both pregnancy and sexually transmitted diseases. Health care providers should be aware of the possible pharmacokinetic interactions between hormonal contraception and antiretrovirals. There is an urgent need for more information regarding metabolic outcomes of hormonal contraceptives, especially the effect of injectable progestins on bone metabolism, in HIV-positive adolescent girls.

Contraception and HIV infection in women

BACKGROUND

More than 15 million women, many of reproductive age, were infected with human immunodeficiency virus (HIV) at the end of 2007. As the HIV epidemic evolves, heterosexual intercourse is increasingly risky: the risk of infection in exposed young women is 4- to 7-fold higher than in young men and nearly half a million newborns annually have HIV. This review aims to show the effect of contraceptive choices on risk of HIV and on the course of disease in women with HIV.

METHODS

Relevant citations were selected by agreement between the authors after a search of MEDLINE using the terms HIV/AIDS and contraception.

RESULTS

Risk of transmission of HIV varies from 1 in 200 to 1 in 10 000 coital incidents, depending in part on the integrity of the vaginal epithelium. Consistent use of male condoms has been proven to reduce horizontal transmission of HIV by 80% among HIV-serodiscordant couples. Hormonal contraception may increase the risk of HIV acquisition in high-risk women such as commercial sex workers, but not in women at low risk of HIV. While hormonal contraception did not affect progression of disease in two cohort studies involving 370 women, in a randomized trial among women not receiving antiretroviral medication, clinical disease accelerated in the oral contraception group (13.2/100 woman-years) compared with the copper intrauterine devices group (8.6/100 woman-years; hazard ratio, 1.5; 95% confidence interval, 1.04-2.1). Hormonal contraception does not interfere with antiviral drug effectiveness.

CONCLUSIONS

All the available reversible contraceptive methods can generally be used by women at risk of HIV infection and by HIV-infected women. Further studies are needed to investigate the safety and efficiency of hormonal contraception in women living with HIV/AIDS.

Effects of HIV antiretrovirals on the pharmacokinetics of hormonal contraceptives

OBJECTIVES

To review available information on pharmacokinetic effects of HIV antiretrovirals on hormonal contraceptives.

METHODS

A PubMed search was conducted from 1964 to 2006 using each antiretroviral generic name and the keywords contraceptive, contraception, ethinyl oestradiol, oestrogen, and progestin. Abstracts from the annual Conference on Retroviruses and Opportunistic Infections and International AIDS Society Conferences from 1998-2006 as well as package product inserts were reviewed for completeness.

RESULTS

Antiretroviral regimens containing protease inhibitors and non-nucleoside reverse transcriptase inhibitors may decrease the area under the curve (AUC) levels of steroids released by hormonal contraceptives. Some antiretroviral-hormonal contraceptive pairs do not decrease steroid hormone levels.

CONCLUSION

Pharmacokinetic interactions of antiretrovirals on hormonal contraceptives are specific to the type of antiretroviral and hormonal contraceptive being utilized. HIV-positive women may be counselled to use dual methods of hormonal and barrier contraception to prevent pregnancy with maximal efficacy as well as to reduce possibility of HIV transmission. Oral contraceptives might be administered with non-ritonavir boosted atazanavir or non-ritonavir boosted indinavir without a loss of contraceptive efficacy. Depot medroxyprogesterone acetate may be safe to administer with efavirenz, nevirapine, and nelfinavir. However, further studies are needed to determine the clinical relevance of the interactions between hormonal contraceptives and antiretrovirals and to explore potential dose adjustments to improve contraceptive efficacy.

Influence of adenosine triphosphate and ABCB1 (MDR1) genotype on the P-glycoprotein-dependent transfer of saquinavir in the dually perfused human placenta

BACKGROUND

The ATP-dependent drug-efflux pump, P-glycoprotein (P-gp) encoded by ABCB1 (MDR1), plays a crucial role in several tissues forming blood-tissue barriers. Absence of a normally functioning P-gp can lead to a highly increased tissue penetration of a number of clinically important drugs.

METHODS

We have studied the dose-response effect of exogenous ATP on the placental transfer of the well-established P-gp substrate saquinavir in 17 dually perfused human term placentas. We have also studied the influence of the ABCB1 polymorphisms 2677G>T/A and 3435C>T on placental P-gp expression (n = 44) and the transfer (n = 16) of saquinavir.

RESULTS

The present results indicate that the addition of exogenous ATP to the perfusion medium does not affect the function of P-gp as measured by saquinavir transfer across the human placenta. The variant allele 3435T was associated with significantly higher placental P-gp expression than the wild-type alleles. However, neither polymorphism affected placental transfer of saquinavir nor there was any correlation between P-gp expression and saquinavir transfer.

CONCLUSIONS

Our results indicate that addition of exogenous ATP is not required for ATP-dependent transporter function in a dually perfused human placenta. Although the ABCB1 polymorphism 3435C>T altered the expression levels of P-gp in the human placenta, this did not have any consequences on P-gp-mediated placental transfer of saquinavir.

Pharmacokinetic Interaction between Ethinyl Estradiol, Norethindrone and Darunavir with Low-Dose Ritonavir in Healthy Women

Background

An open-label, randomized, crossover study was performed to investigate the effect of multiple doses of darunavir co-administered with low-dose ritonavir (DRV/r) on the steady-state pharmacokinetics of the oral contraceptives ethinyl estradiol (EE) and norethindrone (NE) (commercial name of the combined drug Ortho-Novum 1/35) in 19 HIV-negative healthy women.

Methods

In session 1, participants received 35 μg EE and 1.0 mg NE from days 1 to 21. In session 2, participants received the same oral contraceptive treatment as in session 1 on days 1 to 21 plus DRV/r (600 mg/100 mg twice daily) on days 1 to 14. Pharmacokinetic assessments were performed on day 14 for each session.

Results

Steady-state systemic exposure to EE and NE decreased when DRV/r was co-administered, based on the ratio of least square means of the minimum plasma concentration (Cmin), the maximum plasma concentration (Cmax), and the area under the curve (AUC24h) of EE (which decreased by 62%, 32% and 44%, respectively) and NE (which decreased by 30%, 10% and 14%, respectively) compared with administration of EE and NE alone. Five participants discontinued the study due to grade 2 cutaneous events, as required per protocol, during treatment with EE and NE in combination with DRV/r. There were no clinically relevant findings for laboratory and cardiovascular parameters.

Conclusions

The pharmacokinetic interaction observed here is considered to be clinically relevant as EE concentrations are considerably reduced when DRV/r is co-administered with EE and NE. Alternative or additional contraceptive measures should be used when oestrogen-based contraceptives are co-administered with DRV/r.

Gender: a possible determinant in dosing of dermatologic drugs--an overview

The role of gender in pharmacokinetics could play a significant role in tailoring HIV and other drug regimens. Here we investigate sex as a factor in saquinavir pharmacokinetics. The HIV-positive women who use saquinavir in combination with other protease inhibitors frequently demonstrate higher saquinavir concentrations than their male counterparts. The majority of the data indicates that the root of women's higher saquinavir concentrations is not inherent to their gender. Rather, extenuating factors associated with HIV play a prominent role in the observed difference between men and women's pharmacokinetic parameters. The source of observed differences in saquinavir pharmacokinetics could not be definitively traced to CYP3A, the enzyme responsible for saquinavir's metabolism or drug transporters. Hormonal changes associated with HIV infection together with concurrent use of other protease inhibitors could help explain development of sex differences. These findings can be used to further investigate when and why gender-based differences in saquinavir pharmacokinetics exist and possible future dosage and therapy considerations. Our knowledge of gender-related pharmacokinetics should be extended for other systemic drugs in dermatology.

Gender-specific considerations in the antiretroviral management of HIV-infected women

The vast majority of HIV-infected women are of childbearing potential, so issues surrounding reproduction and mother-to-child transmission of the virus are critical in the management of this population. Optimal antiretroviral management of pregnant women is a major global issue since antiretroviral regimens offered to pregnant women to decrease mother-to-child transmission in many countries are often not highly active against HIV. The subsequent emergence of resistant virus can have long-term sequelae for the mother, child, and ultimately, other exposed individuals. The efficacy of antiretroviral therapy appears similar in men and women, although women may experience higher toxicity profiles, which may, in turn, be related to the higher antiretroviral concentrations shown in pharmacokinetic studies. Further investigation into gender-related issues, including sex-associated antiretroviral toxicities, unique pharmacokinetic profiles and optimal antiretroviral management during pregnancy is needed.

MDR1 genotype-related pharmacokinetics: fact or fiction?

Multidrug resistant transporter MDR1/P-glycoprotein, the gene product of MDR1, is a glycosylated membrane protein of 170 kDa, belonging to the ATP-binding cassette superfamily of membrane transporters. A number of various types of structurally unrelated drugs are substrates for MDR1, and MDR1 and other transporters are recognized as an important class of proteins for regulating pharmacokinetics. The first investigation of the effects of MDR1 genotypes on pharmacotherapy was reported in 2000; a silent single nucleotide polymorphism (SNP), C3435T in exon 26, was found to be associated with the duodenal expression of MDR1, and thereby the plasma concentration of digoxin after oral administration. In the last 5 years, clinical studies have been conducted around the world on the association of MDR1 genotype with MDR1 expression and function in tissues, and with the pharmacokinetics and pharmacodynamics of drugs; however, there are still discrepancies in the results on C3435T. In 1995, a novel concept to predict in vivo oral pharmacokinetic performance from data on in vivo permeability and in vitro solubility has been proposed, and this Biopharmaceutical Classification System strongly suggested that the effects of intestinal MDR1 on the intestinal absorption of substrates is minimal in the case of commercially available oral drugs, and therefore MDR1 genotypes are little associated with the pharmacokinetics after oral administration. This review summarizes the latest reports for the future individualization of pharmacotherapy based on MDR1 genotyping, and attempts to explain discrepancies.

Sex Differences in Antiretroviral Therapy-Associated Intolerance and Adverse Events

Although women account for a substantial proportion of the global population infected with HIV, most clinical trials evaluating the safety and efficacy of specific antiretroviral therapy regimens have been preformed in predominantly male cohorts. Our knowledge of the sex differences associated with responses to these treatments is therefore limited. Potentially sex-specific influences, such as endogenous or exogenous hormones, could impact antiretroviral tolerance. Women also have different pharmacokinetic profiles for selected antiretrovirals compared with men. These factors could influence how women respond and react to antiretrovirals. Several observational studies have described a higher frequency of antiretroviral-related adverse effects among women compared with men. Women appear to be at an especially high risk for lactic acidosis, nevirapine-associated rashes and hepatotoxicity, and fat redistribution after highly active antiretroviral therapy exposure. Although a statistical association between antiretroviral toxicity and pregnancy has not been described, pregnancy may provide an additional influence on the toxicity of several antiretrovirals or antiretroviral combinations. Potential tolerability should be an important component in discussions of antiretroviral options among women.

In vitro and ex vivo evidence for modulation of P-glycoprotein activity by progestins

The well known gender-related differences in drug action may partly be explained by changes in activity and expression of drug metabolising enzymes, but also by modulation of active drug transport systems (e.g. P-glycoprotein, Pgp) by sexual steroids, which is yet not well investigated. Because many women are using hormones (e.g. as oral contraceptives) we investigated the influence of different synthetic progestins on Pgp activity. Pgp inhibition of progesterone, medroxyprogesterone, chlormadinone, cyproterone, levonorgestrel, norethisterone, desogestrel, and norgestimate was measured in vitro in two Pgp over-expressing cell lines (L-MDR1, P388/dx cells) and the corresponding parental cell lines by means of calcein assay, and ex vivo in human peripheral blood mononuclear cells (PBMCs) by rhodamine123 efflux. For most progestins tested, concentrations needed to double baseline fluorescence (f2) in L-MDR1 cells were similar to that of the potent Pgp inhibitor quinidine, whereas levonorgestrel and norethisterone did not reach f2. The results in P388/dx cells essentially confirmed our findings in L-MDR1 cells. Additionally, Pgp inhibitory activity of all progestins tested was also shown ex vivo in PBMCs. The potent Pgp inhibition by several synthetic progestins in vitro and ex vivo suggests that such an interaction might be clinically relevant despite generally low plasma concentrations of progestins. The results may be of particular importance for Pgp substrates, such as protease inhibitors and chemotherapeutic agents, for which intracellular concentrations are critical.