Analysis of Drug-Drug Interaction Labeling Language and Clinical Recommendations for Newly Approved Drugs Evaluated With Digoxin, Midazolam, and S-Warfarin

Abstract

Purpose: To best promote drug tolerability and efficacy in the clinic, data from drug-drug interaction (DDI) evaluations and subsequent translation of the results to DDI prevention and/or management strategies must be incorporated into the US Food and Drug Administration (FDA) product labeling in a consistent manner because differences in language might result in varied interpretations. This analysis aimed to assess the consistency in DDI labeling language in New Drug Applications (NDAs).

Methods: NDAs of recently approved drugs (2012-2020) that increase the exposure of digoxin, midazolam, and S-warfarin, index substrates of P-glycoprotein, cytochrome P450 (CYP) 3A, and CYP2C9 activity, respectively, were fully reviewed. Noninhibitors were also evaluated to appreciate the extent of mechanistic extrapolation in case of negative index studies.

Findings: After a systematic review of the DDI studies available in NDAs, FDA-approved labeling, and commonly used clinical tertiary resources, differences in DDI results presentation and resulting clinical recommendations were found, even for inhibitors that affect similarly the exposure of the same index substrate. Studies with negative results were often reported in the labels without providing mechanistic interpretation, thus limiting the possible extrapolation of this information to other known substrates.

Implications: The variability in language affects how the information was presented to clinicians in tertiary resources. Strategies that aim to improve the translation of mechanistic DDI index studies into consistent labeling recommendations are briefly discussed in this review.

Keywords: drug-drug interactions; labeling; newly approved drugs; regulatory.