Sex-by-formulation interaction assessed through a bioequivalence study of efavirenz tablets

Considerations of sex in bioequivalence assessments: does sex affect pharmacokinetic variability between evaluation formulations?

BACKGROUND

Bioequivalence assessment determines the equivalence between drug formulations and is primarily used to demonstrate that a generic product is equivalent to its reference. The sex of the drug consumer is a major consideration in bioequivalence assessment, but specific ratios or absolute criteria for sex composition are usually not specified.

PURPOSE

This study explored whether the sex of participants in a bioequivalence assessment could significantly affect the pharmacokinetic variability between formulations and decision outcomes. In bioequivalence studies, the sex composition should reflect the drug's target population, but it is often acceptable to limit it to healthy adult males. Therefore, it is essential to consider the variation in bioequivalence results according to sex.

METHODS

Levocetirizine and rabeprazole enteric-coated tablets were chosen as investigational agents, and clinical trial data for these were used in the bioequivalence analysis. This analysis was conducted both with and without considering sex, and the final determination of equivalence was based on whether the 90% confidence interval for the ratio of standard pharmacokinetic parameters between the reference and test formulations fell within the 80 to 125% range. Additionally, principal component analysis (PCA) was performed to determine whether there were significant differences in the targeted pharmacokinetic parameter values between drug formulations across each sex group.

RESULTS

Bioequivalence of levocetirizine's reference and test formulations was confirmed, independent of sex. For rabeprazole, bioequivalence was established in males-even without considering sex-but not in females, based on extended criteria for drugs with significant pharmacokinetic variability. The PCA results also showed that there were significant differences (P < 0.05) in the distribution of pharmacokinetic parameters of rabeprazole by gender and formulation. This indicates that equivalence assessments may vary based on pharmacokinetic differences related to sex among subjects in bioequivalence studies. Thus, it was shown that sex may influence pharmacokinetic variability between reference and test formulations of the same drug.

CONCLUSION

This study provided valuable insights into the role of sex in bioequivalence studies. For drugs exhibiting significant pharmacokinetic differences between sexes, it is crucial to recognize that bioequivalence results may vary based on the sex ratio in the participant group. Therefore, further analysis and interpretation, taking sex-related factors into account, will be necessary during bioequivalence evaluations.

Perspective on statistical power and equivalence tests

The use of both sexes or genders should be considered in experimental design, analysis, and reporting. Since there is no requirement to double the sample size or to have sufficient power to study sex differences, challenges for the statistical analysis can arise. In this article, we focus on the topics of statistical power and ways to increase this power. We also discuss the choice of an appropriate design and statistical method and include a separate section on equivalence tests needed to show the absence of a relevant difference.

Investigation on the Existence of Sex-By-Formulation Interaction in Bioequivalence Trials

The US Food and Drug Administration recommends that if a drug product is intended for use in both sexes, similar proportions should be recruited for bioequivalence (BE) studies. In contrast, in Europe, subjects can belong to either sex. Literature suggesting the existence of sex-by-formulation interaction (S × F) is limited to few studies. To investigate if S × F is observed, this work includes 120 BE studies. Differences larger than 20% between the ratio test/reference of women and men or statistically significant S × F occurred in 25 of 120 studies (20.8%). The prevalence is higher in small studies (36.00% vs. 16.8%). Large differences between the ratios of the sex groups are the tails of the distribution. Two studies were repeated, and the differences between the ratios of the sex groups disappeared. The 90% confidence intervals of S × F did not confirm any relevant S × F. There is no evidence to require studies in both sex groups, combined or separately.

Sex-by-formulation interaction in bioequivalence trials with transdermal patches

PURPOSE

The existence of a sex-by-formulation interaction in bioequivalence studies implies that the bioequivalence results (i.e., the test/reference ratio of the pharmacokinetic parameters) obtained in one sex are not similar to those obtained in the other sex. Therefore, results obtained in studies including only males may not be representative of the results obtained in females and vice versa. The best evidence of the existence of a sex-by-formulation interaction has been obtained from a study conducted with transdermal patches. This observation might be caused by the different characteristics of the skin of males and females. The purpose of this work is to investigate the existence of a sex-by-formulation interaction in all bioequivalence studies of transdermal patches submitted to the Spanish Agency for Medicines between 2010 and 2016.

METHODS

Only five different products (Buprenorphine-1, Fentantyl-1, Fentanyl-2, Rivastigmine-1 and Rivastigmine-2) that were submitted for registration included nine bioequivalence studies conducted in males and females. As single dose and multiple dose studies are required for registration of transdermal patches in the European Union, more than one study may be available to confirm the existence of a sex-by-formulation interaction.

RESULTS

A sex-by-formulation interaction is suggested in six out of 27 datasets (22%), corresponding to two products, and it is statistically significant in three of them (11%).

CONCLUSIONS

The sex-by-formulation interaction detected in some pharmacokinetic parameters of some studies is excluded when the study is repeated, which shows that these results are not reproducible. There is no evidence to require bioequivalence demonstration for transdermal patches in males and females separately.

Sex-by-formulation interaction in bioequivalence studies: the importance of formulations and experimental conditions

In a recently published investigation, the authors argued against the likelihood of sex-based subject-by-formulation interactions in bioequivalence studies, i.e. male and female subjects exhibiting different discriminatory potential to detect bioavailability differences between formulations. The researchers performed a strong methodological study showing the increased probability of false-positive findings in exploratory subgroup analysis, a well-known and documented statistical issue. Indeed, the main limitation of assessing a sex-by-formulation interaction in average bioequivalence studies lies in the fact that these clinical trials are not designed for this purpose. In this commentary, we further discuss on why the impact of sex differences in gastrointestinal physiology over in vivo drug dissolution and absorption rate cannot remain hidden behind statistical limitations, particularly when average bioequivalence conclusions could be affected. Regulatory agencies should encourage and support these important issues related to biopharmaceutical quality of drug products in both sexes. In addition, a sex-based analysis of bioequivalence results will enhance the representativeness of conclusions and provide important information regarding formulation performance, thereby promoting the efficacy and safety of generic drugs and reducing consumer risk. The extrapolation of study conclusions from one sex to another is far away from being scientifically proven.

Evaluation of sex-by-formulation interaction in bioequivalence studies of efavirenz tablets

AIMS

The existence of a sex-by-formulation interaction in bioequivalence studies implies that the bioequivalence results (i.e., the test/reference ratio of the pharmacokinetic parameters) obtained in one sex are not similar to those obtained in the other sex. Therefore, results obtained in studies including only males would not be representative of the results that would have been obtained in females and vice versa. Recently, a sex-by-formulation interaction has been reported in a study for efavirenz tablets. The purpose of this paper is to investigate whether a sex-by-formulation interaction is actually observed in the bioequivalence studies conducted with efavirenz tablets.

METHODS

The existence of sex-by-formulation interaction was investigated in the two studies conducted in our centre, where the same test and reference products were investigated in a pilot study with 12 subjects and a pivotal study with 36 subjects.

RESULTS

In the pilot study, the point estimates for the test/reference ratio of geometrics means of C_max in females and males were more than 20% different (95.42% vs.79.38%, i.e., 120.21%), but in a subsequent pivotal study the difference was less than 2% (111.14% vs. 109.98%, i.e., 101.66%).

CONCLUSIONS

A sex-by-formulation interaction is suggested in the study with a small sample size, but it disappears when the study is repeated with a larger sample size. In conclusion, the analysis of subgroups should be conducted with caution when the size of the subgroups is not powered to show bioequivalence. There seems to be no reason to require bioequivalence studies for efavirenz in both sexes.

Integration of in vitro biorelevant dissolution and in silico PBPK model of carvedilol to predict bioequivalence of oral drug products

Bioequivalence implementation in developing countries where a high proportion of similar drug products are being marketed has found several obstacles, impeding regulatory agencies to move forward with this policy. Biopharmaceutical quality of these products, several of which are massively prescribed, remains unknown. In this context, an in vitro-in silico-in vivo approach is proposed as a mean to screen product performance and target specific formulations for bioequivalence assessment. By coupling in vitro biorelevant dissolution testing in USP-4 Apparatus (flow-through cell) with physiologically-based pharmacokinetic (PBPK) modeling in PK-Sim® software (Bayer, Germany), the performance of seven similar products of carvedilol tablets containing 25 mg available in the Uruguayan market were compared with the brand-name drug Dilatrend®. In silico simulations for Dilatrend® were compared with published results of bioequivalence studies performed in fasting conditions allowing model development through a learning and confirming process. Single-dose pharmacokinetic profiles were then simulated for the brand-name drug and two similar drug products selected according to in vitro observations, in a virtual Caucasian population of 1000 subjects (50% male, aged between 18 and 50 years with standard body-weights). Population bioequivalence ratios were estimated revealing that in vitro differences in drug release would have a major impact in carvedilol maximum plasma concentration, leading to a non-bioequivalence outcome. Predictions support the need to perform in vivo bioequivalence for these products of extensive use. Application of the in vitro-in silico-in vivo approach stands as an interesting alternative to tackle and reduce drug product variability in biopharmaceutical quality.

Sex Effect on Average Bioequivalence

PURPOSE

Generic formulations are by far the most prescribed drugs. This scenario is highly beneficial for society because medication expenses are significantly reduced after expiration of the exclusivity period conceded to the branded name drug. Correspondingly, these formulations must be adequately evaluated to avoid drug inefficacy and toxicity in the overall patient population. Bioequivalence studies are the only in vivo evaluation that a generic drug must overcome to reach the market. These clinical trials have not been exempt from underrepresentation of female subjects and a lack of sex-based analysis. Frequently, conclusions obtained in men are extrapolated to women. Furthermore, the obtained results are not analyzed to determine sex differences. The aim of this study was to discuss the effect that male and female differences in gastrointestinal physiology can have on bioequivalence conclusions and to show why a sex-based analysis must be conducted in these studies to improve the evaluation of generic drugs.

METHODS

This discussion was based on observed sex differences in product bioavailability discrimination (sex-by-formulation interaction) and on residual variability through an analysis of average bioequivalence data previously reported by other researchers and data collected by our center. Bioequivalence studies of oral formulations, with a 2-period, 2-sequence, 2-treatment random crossover design performed in healthy subjects with at least 6 subjects of each sex, were included. In addition, the bioequivalence conclusion that would have been reached in each study if performed with only 1 sex was estimated.

FINDINGS

The data reveal that differences in both product bioavailability discrimination and residual variability occur with a significant incidence in bioequivalence studies. In either C_max or AUC, a significant sex-by-formulation interaction was present in 1 of 3 reviewed studies, whereas differences in residual variability between sexes were significant for >50% of studies. Moreover, the performed estimations suggest that the reported bioequivalence conclusions were not verified in at least 1 sex for 1 of 3 studies and were not verified in men and in women for 1 of 6 studies.

IMPLICATIONS

This research shows that extrapolation of bioequivalence results from the male population to the female population is not always valid. Bioequivalence studies must therefore be performed with both male and female subjects in similar proportions. Sex-based analysis in bioequivalence can improve study design, enhance the representativeness of conclusions, and provide important information regarding formulation performance, thereby promoting the efficacy and safety of generic drugs.

Physiologically-based pharmacokinetic models: approaches for enabling personalized medicine

Personalized medicine strives to deliver the 'right drug at the right dose' by considering inter-person variability, one of the causes for therapeutic failure in specialized populations of patients. Physiologically-based pharmacokinetic (PBPK) modeling is a key tool in the advancement of personalized medicine to evaluate complex clinical scenarios, making use of physiological information as well as physicochemical data to simulate various physiological states to predict the distribution of pharmacokinetic responses. The increased dependency on PBPK models to address regulatory questions is aligned with the ability of PBPK models to minimize ethical and technical difficulties associated with pharmacokinetic and toxicology experiments for special patient populations. Subpopulation modeling can be achieved through an iterative and integrative approach using an adopt, adapt, develop, assess, amend, and deliver methodology. PBPK modeling has two valuable applications in personalized medicine: (1) determining the importance of certain subpopulations within a distribution of pharmacokinetic responses for a given drug formulation and (2) establishing the formulation design space needed to attain a targeted drug plasma concentration profile. This review article focuses on model development for physiological differences associated with sex (male vs. female), age (pediatric vs. young adults vs. elderly), disease state (healthy vs. unhealthy), and temporal variation (influence of biological rhythms), connecting them to drug product formulation development within the quality by design framework. Although PBPK modeling has come a long way, there is still a lengthy road before it can be fully accepted by pharmacologists, clinicians, and the broader industry.

Complete dataset for 2-treatment, 2-sequence, 2-period efavirenz bioequivalence study conducted with nightly dosing

The efavirenz pharmacokinetic raw data presented in this article was obtained in an average bioequivalence study between a local brand and Stocrin (Merck Sharp & Dohme, purchased from Australia, batch H009175, expiration date November 2013). Dose was administered at night (9:00 p.m.) two hours after food intake. Fourteen healthy subjects, 8 women and 6 men, completed the study. For each subject, 15 data points until 96 h post-administration are included. Subject demographic characteristics and sequences of administration are provided along with individual pharmacokinetic profiles of efavirenz obtained for both formulations after a single oral dose of 600 mg. This data provides information in support of the research article “Sex-by-formulation interaction assessed through a bioequivalence study of efavirenz tablets” [1].