Evaluating gender effect in the generic bioequivalence studies by physiologically based pharmacokinetic modeling - A case study of dextromethorphan modified release tablets

The United States Food and Drug Administration guidelines for the bioequivalence (BE) testing of the generic drug products suggests that there should be an equal proportion of male and female population in the BE study. Despite this requirement, many generic drug companies do not maintain the suggested proportion of female population in their studies. Several socio-economic and cultural factors lead to lower participation of the females in the BE studies. More recently, the regulatory agencies across the globe are requesting the generic drug companies to demonstrate the performance of their drug products in the under-represented sex via additional studies. In this work, we describe the case of Dextromethorphan modified release tablets where the gender effect on the product performance was evaluated by physiologically based pharmacokinetic (PBPK) modeling approach. We have compared the drug product's performance by population simulations considering four different scenarios. The data from all-male population (from in house Pharmacokinetic [PK] BE studies) was considered as a reference and other scenarios were compared against the all-male population data. In the first scenario, we made a comparison between all-male (100% male) vs all-female (100% female) population. Second scenario was as per agency's requirements-equal proportion of male and female in the BE study. As an extreme scenario, 100% male vs 30:70 male:female was considered (higher females than males in the BE studies). Finally, as a more realistic scenario, 100% male versus 70:30 male:female was considered (lower females than males in the BE studies). Population PK followed by virtual BE was employed to demonstrate the similarity/differences in the drug product performance between the sexes. This approach can be potentially utilized to seek BE study waivers thus saving cost and accelerating the entry of the generic products to the market.

Sex differences in the pharmacokinetics and bioequivalence of the delayed-release combination of doxylamine succinate-pyridoxine hydrochloride; implications for pharmacotherapy in pregnancy

Most bioequivalence (BE) studies are conducted in males with the assumption that variability in pharmacokinetics is similar between the sexes. The purpose of this single-center, reference replicate study was to determine the effect of sex on the pharmacokinetics and BE of doxylamine-pyridoxine 10 mg-10 mg delayed-release tablets. Healthy males (n = 12) and non-pregnant females (n = 12) were administered two tablets, and blood sampling was conducted from 1 hour pre-dose until 72 hours post-dose. After 21 days, dose administration and blood sampling were re-conducted. All analytes were measured using liquid chromatography-tandem mass-spectrometry. Pharmacokinetic parameters were calculated for each study period using standard, non-compartmental methods, and differences were assessed using ANOVA. BE testing was conducted using the relative 90% confidence interval for the AUC0-t for each analyte. Females had significantly larger AUC0-t for doxylamine, 1,550 ng h/mL (coefficient of variance [CV = 19%]) versus 1,272 ng h/mL (CV = 21%; P ≤ .05), and pyridoxine, 35 ng h/mL, (CV = 43%) versus 25 ng h/mL (CV = 31%; P ≤ .05) compared to males. A higher Cmax for doxylamine was observed in females, 107 ng/mL (CV = 16%), compared to males, 86 ng/mL (CV = 15%) (P ≤ .05). BE testing did not demonstrate bioequivalence between males and females. Pharmacokinetic differences observed between the sexes have implications for future BE studies using doxylamine-pyridoxine.

Biologic and molecular mechanisms for sex differences in pharmacokinetics, pharmacodynamics, and pharmacogenetics: Part II

There are specific pharmacology issues related to women's unique physiology, including the hormonal changes that occur throughout their life span. Studies have shown alterations in drug metabolism in relation to phase of menstrual cycle, during pregnancy, or after menopause. In the brain, hormones can alter the response to drugs through various mechanisms. Estrogen and other compounds can bind to the estrogen receptor and modulate a wide range of activities within the cell. In addition, animal studies have demonstrated sexual dimorphism in the brain in terms of both the type of response to estrogen and the response as related to timing of administration. Many normal physiological changes that occur during pregnancy can affect pharmacokinetics and pharmacodynamics. These changes during pregnancy are dramatic rises in levels of estrogen and progesterone, increases in maternal blood volume, altered protein binding resulting from a drop in albumin levels, and a rise in levels of other plasma proteins. The field of chronobiology offers a way to study these changes in biological functions. Chronopharmacology is the study of how biological rhythms, particularly 24-hour, menstrual cycle, and annual rhythms, impact the pharmacokinetics and pharmacodynamics of drugs as a function of their timing. Chronopharmacokinetics is the study of the absorption, distribution, metabolism, and elimination of medicines according to the time of day, menstrual cycle, or year. In addition to applying chronobiology to the study of drugs used in women, new technologies were addressed from computer modeling, pharmacogenetics (genetics of the response to drugs), and in vivo drug metabolism studies.

Reproductive toxicity testing of pharmaceutical compounds to support the inclusion of women in clinical trials

1. The potential for toxicity to reproduction and the developing fetus is an important concern requiring attention during the development of new medicines. However, there are differences in the opinions of the regulatory authorities in Europe, Japan and the USA regarding the nature and amount of data from reproductive toxicity tests that should be available at the various stages of clinical development. 2. Forty-one companies or their subsidiaries from Europe, Japan and the USA provided data for a questionnaire-based study, carried out in 1994, to ascertain the practices of pharmaceutical companies and their views on an ideal approach to the timing of reproduction and development toxicity studies in relation to clinical investigation. 3. Differences were identified in the stage of drug development at which animal studies were completed, the sequence of completion of specific studies, and the extent of reproduction testing completed to support the inclusion of women in clinical trials. 4. A harmonised, but flexible, guidelines, encompassing the timing of reproductive toxicity studies in relation to clinical trials, would permit better integration between clinical and non-clinical studies in an international drug development programme.