CYP2D6-inhibiting drugs and risk of fall injury after newly initiated therapy with beta-blockers-a register-based case-crossover study.

We assessed whether concomitant use of CYP2D6-inhibiting drugs associates with increased risk of fall injuries after newly initiated therapy with beta-blockers. A case-crossover study design was applied which eliminates confounding from individual fixed characteristics by pairing cases with themselves across time. Data on prescribed and dispensed beta-blockers and hospitalizations for first-time fall injuries in the Swedish population aged ≥ 20 for the period 2006-01-01-2013-12-31 were extracted from national registers. Odds ratios (OR) with 95% confidence interval (CI) of fall injury associated with newly initiated beta-blocker therapy (prescription dispensed within the 28 days preceding the fall injury) while considering concomitant use of CYP2D6-inhibiting drugs, were estimated. Newly initiated beta-blocker therapy (any type) with concomitant use of CYP2D6-inhibiting drugs (any type) was associated with an increased risk of fall injury (OR 1.37, 1.24-1.52). This risk became elevated after restriction to concomitant use of moderate (OR 1.63, 1.26-2.10) or strong CYP2D6 inhibitors (OR 2.25, 1.39-3.63). The results remained similar independent of the beta-blockers' degree of CYP2D6 metabolism (none, partial or major). Our study indicates the presence of drug-drug interaction for concomitant use of beta-blockers and CYP2D6 inhibitors in relation to the risk of fall injury, irrespective of degree of CYP2D6 metabolism.