(M1330-11-65) The Impact of Back Conversion of Acyl Glucuronide Metabolites on the Bioequivalence Studies Submitted in Abbreviated New Drug Applications

Purpose: The bioanalysis of drugs that undergo acyl glucuronidation represents an analytical challenge due to poor stability of acyl glucuronide metabolites in biological matrices. The purpose of this study is to investigate the impact of back conversion of acyl glucuronide metabolites on the drug concentration measurement in the bioequivalence (BE) studies submitted in Abbreviated New Drug Applications (ANDAs) by analyzing the prevalence of the treatments in preventing the back conversion of acyl glucuronide metabolites and the results of incurred sample reanalysis (ISR).

Methods: The data of ISR, method validation with acyl glucuronide metabolites, and the back conversation prevention treatments (lower pH, lower temperature, adding inhibitors/stabilizers) during the collection, processing, and extraction of study samples are collected from 346 ANDAs for 27 drugs known to generate acyl glucuronide metabolites. The non-parametric sign test was applied to evaluate if the ISR results are statistically higher than those of the corresponding original samples, suggesting a conversion of acyl glucuronide metabolites back to parent drugs. The effects of treatments of study samples, in preventing the back conversion of acyl glucuronide metabolites, on the ISR results were evaluated using the logistic regression.

Results: Among ANDAs for the drugs known to generate acyl glucuronide metabolites, only a small fraction (16.5%) conducted the validation on the detection of analytes in the presence of acyl glucuronide metabolites. For the prevalence of prevention treatments, more than two-third (67.9%) of the studies contains the procedures of lowering temperature for sample collection in the clinical phase. There are fewer studies contain the procedures of lowering pH of plasma samples (12.0%) or adding inhibitors/stabilizers (4.2%) during study sample collection phase. The majority (62.4%) of studies has the procedures of lowering pH during the sample extraction process in the bioanalytical phase. Approximately 28.8% of studies have significantly higher (p-value < 0.01 by sign test) ISR results than the corresponding original concentration values. Although lack of the prevention treatments is not statistically associated with higher ISR results, a very small portion (3.5%) of BE studies for the drugs known to generate reactive acyl glucuronide metabolites had higher ISR results but without any prevention treatments during bioanalysis, suggesting that back conversion of acyl glucuronide metabolites to parent drugs may be prominent for these studies.

Conclusion: The majority of ANDAs under investigation contain treatments in preventing the back conversion of acyl glucuronide metabolites. Combined with the prevention treatments, ISR data may be helpful in identifying the potential back-conversion of acyl glucuronide metabolites. The findings will benefit the Agency in the scientific evaluation of the impact of acyl glucuronide metabolites and its impact on the review timelines in order to be meet the user fee program commitments.