Interrelationship of serum levonorgestrel and sex hormone-binding globulin levels following vaginal and oral administration of combined steroid contraceptive tablets

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.

The Effect of Gene Variants on Levonorgestrel Pharmacokinetics When Combined With Antiretroviral Therapy Containing Efavirenz or Nevirapine

Reduced levonorgestrel concentrations from the levonorgestrel contraceptive implant was previously seen when given concomitantly with efavirenz. We sought to assess whether single nucleotide polymorphisms (SNPs) in genes involved in efavirenz and nevirapine metabolism were linked to these changes in levonorgestrel concentration. SNPs in CYP2B6, CYP2A6, NR1I2, and NR1I3 were analyzed. Associations of participant demographics and genotype with levonorgestrel pharmacokinetics were evaluated in HIV-positive women using the levonorgestrel implant plus efavirenz- or nevirapine-based antiretroviral therapy (ART), in comparison to ART-naïve women using multivariate linear regression. Efavirenz group: CYP2B6 516G>T was associated with lower levonorgestrel log₁₀ C_max and log₁₀ AUC. CYP2B6 15582C>T was associated with lower log₁₀ AUC. Nevirapine group: CYP2B6 516G>T was associated with higher log₁₀ C_max and lower log₁₀ C_min . Pharmacogenetic variations influenced subdermal levonorgestrel pharmacokinetics in HIV-positive women, indicating that the magnitude of the interaction with non-nucleoside reverse transcriptase inhibitors (NNRTIs) is influenced by host genetics.

Metabolism of endogenous and exogenous reproductive hormones

Estradiol and progesterone are produced in abundance by the ovary of the reproductive-age female (and by the placenta in pregnancy). Serum levels of both hormones are very low in the postmenopause, and indistinguishable from women who have undergone castration. Postmenopausal women have higher levels of aromatase in skin and adipose and convert androstenedione to estrone more effectively than younger women. Estradiol is well absorbed orally, but undergoes extensive first-pass effect resulting in production of the less potent metabolites estrone and estrone sulfate. Ethinyl estradiol is well absorbed, potent, and has more pronounced effects in the production of important hepatic proteins. Progesterone is absorbed orally only if ingested in a micronized form, has a relatively short serum half-life, and is metabolized to products with little biologic activity. The synthetic progestogens are abundant in number; potent in effect; and well absorbed orally, vaginally, and transdermally. New formulations of estrogens and progestogens and new delivery systems promise to provide gynecologists and patients with a long list of potential solutions to contraceptive needs and alternatives for hormone replacement therapies.