Invited Commentary: Building rigorous clinical evidence for drug-drug interactions.

Drug-drug interactions (DDIs) are a major cause of preventable adverse drug events. However, the clinical relevance of specific DDIs is often uncertain due to limited evidence beyond preclinical findings and pharmacokinetic studies. In this editorial, we discuss the recent study by Bea et al. (Am J Epidemiol. 0000;000(00):0000-0000), which assessed whether the pharmacologic interaction between hydrocodone and non-dihydropyridine calcium-channel blockers is associated with the risk of opioid overdose, finding no increased risk. We highlight the methodological strengths of the study, including the use of a control precipitant, the consideration of the order of drug initiation in concomitant use, and the application of multiple exposure definitions. At the same time, we outline remaining challenges -both in this study and more broadly in the DDI field- such as the appropriate selection of control precipitants and selection bias due to depletion of susceptibles. Finally, we briefly discuss potential applications of novel pharmacoepidemiologic methods for DDI studies and also ways to strengthen the rationale for DDI studies and prioritize study questions. Given the rising rates of polypharmacy that lead to increased concomitant use of medications potentially interacting with each other, pharmacoepidemiology is well-positioned to generate clinically actionable evidence to guide medication safety.