(M1030-06-32) Analytical Considerations of Drug Products Containing Isomeric Active Pharmaceutical Ingredients in Abbreviated New Drug Application (ANDA) Submissions

Purpose: Active pharmaceutical ingredients (API) can exist as isomers, which are chemical compounds with identical molecular formula. Isomers of many drugs can significantly affect the rate and extent of the absorption, distribution, metabolism, and excretion. During bioanalysis of the bioequivalence (BE) study samples for such drugs, a critical component of bioanalytical method validation is to demonstrate the specificity of the method for individual isomer. During simultaneous determination of isomers, monitoring additional peaks and avoiding cross-interference can be challenging, especially when isomers can undergo reversible interconversion. In addition, variation in the ratio of individual isomers amounts between test and reference listed drug (RLD) products can influence the outcome of a BE study where API is a mixture of isomers. This project compiles issues related to the bio-analysis and/or drug product formulation of in-house ANDA submissions for two representative isomeric APIs i.e., Isotretinoin capsules (cis- isomer which can undergo in vivo conversion to trans- isomer, tretinoin) and Phytonadione Tablets (mixture of cis- and trans- isomers), to provide applicants the clarity and recommendations for avoiding encountered issues.

Methods: ANDAs submitted to the Agency for Isotretinoin and Phytonadione drug products from 2010 to 2024 were evaluated for bioequivalence issues. For both the drug products, issues identified in the bio-analytical portions of the ANDAs and consequent deficiencies issued by the Agency were collected. For the phytonadione drug product where API is a mixture of cis- and trans- isomers, the amounts of individual isomers in the generic formulations were collected and correlated with outcome of bioequivalence.

Results: In all the ANDAs collected for Isotretinoin Capsules and Phytonadione Tablets, repeat analysis of study samples due to poor chromatography such as extra peak, split peak and/or interference at retention time of API was observed. Since isotretinoin and tretinoin (retinoic acid) can interconvert in vivo or during sample storage, therefore a cross analyte interference study to avoid repeats due to poor chromatography is required during method validation. Approximately 50% of the ANDA submissions did not include a cross-analyte interference study, resulting in deficiencies being issued. Additionally, for the ANDAs collected for Phytonadione Tablets, approximately in 50% of the submissions, test/reference ratios of pharmacokinetic (PK) parameters for cis- isomer were not within 0.80-1.25 and deficiency was issued. The meta-analysis of these BE studies showed that the point estimates for PK parameters correlated with the difference in potency of cis- isomer in the test as compared to RLD product. After correcting for potency, the point estimates for the PK parameters were found to be within the range of 0.8 to 1.25.

Conclusion: Based on the data collected from in-house ANDA submissions for Isotretinoin Capsules and Phytonadione Tablets, all submissions exhibited issues related to poor chromatography. The pre-study bio analytical method validation for these submissions lacked adequate “specificity” data for individual isomers, resulting in issuance of bioanalytical deficiencies in the BE studies due to cross analyte interference. Specifically, for Phytonadione Tablets, applicants should conduct reverse engineering to maintain the similar ratio of individual isomers amounts in test product as is in the RLD product to demonstrate comparable therapeutic equivalence. In such cases, adhering solely to USP specifications for the amounts of individual isomers may not yield the desirable BE outcome. Overall, this project provides guidance to ANDA applicants to avoid unnecessary deficiencies during approval process, thereby facilitating early access to safe and effective generic drugs to the American public.