Effect of metoprolol exposure following myocardial infarction on future cardiovascular events: a Mendelian randomization study

PURPOSE: The clinical benefit of up-titration of metoprolol to a guideline-recommended target dose after myocardial infarction (MI) is unknown. Our aim was to investigate whether variation in metoprolol exposure determined by cytochrome p450 enzyme 2D6 (CYP2D6) influences the occurrence of major adverse cardiovascular events (MACE) and cardiovascular death (CV death) among patients treated with metoprolol after MI. METHOD: This Mendelian randomization study was performed using individual-level data from 1554 patients treated with metoprolol after an acute MI. CYPD26 genotype was applied as a binary genetic instrument assigning patients into two metoprolol exposure groups: CYP2D6 normal metabolizers (NM) (low exposure) and CYP2D6 intermediate and poor metabolizers (IM + PM) (high exposure). The null hypothesis of no association between the CYP2D6 metabolizer subgroup and MACE or CV death was tested using the Cox proportional hazards model. All-cause mortality and individual components of MACE were included as secondary outcomes. RESULTS: In total, 879 (56.6%) patients were classified as NM and 675 (43.4%) as IM + PM. During the 3-year follow-up, 56 patients (6.4%) in the NM group had an outcome of MACE, and 24 (2.7%) patients died from CV disease. Corresponding frequency in the IM + PM group was 47 (7.0%) and 22 (3.3%), respectively. There was no association between genotype and MACE [unadjusted HR 1.12 (CI 0.76, 1.65)] or CV death [unadjusted HR 1.20 (CI 0.67, 2.14)], or between the CYP2D6 group and any of the secondary outcomes. CONCLUSION: In patients treated with metoprolol after MI, variation in metoprolol exposure determined by CYP2D6 did not impact the occurrence of cardiovascular events.