Adverse events with co-prescription of angiotensin receptor blockers and clarithromycin compared to azithromycin: A population-based retrospective cohort study.

Background: Clinically relevant drug-drug interactions (DDIs) are a common cause of adverse drug reactions (ADRs). Hepatic organic anion transporting polypeptides (OATPs) have recently been studied for their role in DDIs. The commonly prescribed antihypertensive angiotensin receptor blockers (ARBs) are known to be eliminated by hepatic OATPs. ARBs are commonly prescribed to patients with reduced kidney function, and kidney disease can result in profound changes to nonrenal drug elimination through reduced hepatic drug transport-mediated excretion. The antibiotic clarithromycin inhibits OATP activity whereas azithromycin does not, making them useful comparators to study DDIs with OATP substrate drugs.

Objective: To investigate whether co-prescription of ARBs and clarithromycin results in increased adverse events compared to azithromycin and whether kidney function modifies this risk.

Methods: We conducted a retrospective population-based cohort study in Ontario, Canada (2010-2021) using linked health care data for 106,322 older individuals (≥66 years) receiving an OATP substrate ARB (candesartan, olmesartan, telmisartan, valsartan) and newly co-prescribed clarithromycin (n = 32,693) or azithromycin (n = 73,629). Primary outcomes were hospital admissions or emergency department visits for hyperkalemia or acute kidney injury (AKI) within 14 days of antibiotic prescription. Adjusted risk ratios (aRR) were obtained using modified Poisson regression after controlling for eight potential confounders. Pre-specified effect measure modification analysis evaluated whether kidney function influenced these outcomes.

Results: Compared to those co-prescribed azithromycin, patients receiving clarithromycin had a significantly higher risk of hyperkalemia (aRR 2.05, 95% confidence interval (CI) 1.32-3.18) and AKI (aRR 1.75, 95% CI 1.41-2.17). The risk of hyperkalemia increased as kidney function declined (multiplicative interaction; p = 0.01).

Conclusions: This population-based retrospective cohort study provides evidence of OATP-mediated drug interactions between ARBs and clarithromycin that warrants further investigation to guide clinical practice, especially for patients with reduced kidney function.