Genetic variation in the CYP2D6 gene is associated with a lower heart rate and blood pressure in beta-blocker users.

Several beta-blockers are metabolized by the polymorphic enzyme cytochrome P450 2D6 (CYP2D6). CYP2D64 is the main polymorphism leading to decreased enzyme activity. The clinical significance of impaired elimination of beta-blockers is controversial, and most studies suffer from inclusion of small numbers of poor metabolizers (PMs) of CYP2D6. In this study, the association between CYP2D64 and blood pressure or heart rate was examined in 1,533 users of beta-blockers in the Rotterdam Study, a population-based cohort study. In CYP2D6 *4/*4 PMs, the adjusted heart rate in metoprolol users was 8.5 beats/min lower compared with *1/*1 extensive metabolizers (EMs) (P < 0.001), leading to an increased risk of bradycardia in PMs (odds ratio = 3.86; 95% confidence interval 1.68-8.86; P = 0.0014). The diastolic blood pressure in PMs was 5.4 mm Hg lower in users of beta-blockers metabolized by CYP2D6 (P = 0.017) and 4.8 mm Hg lower in metoprolol users (P = 0.045) compared with EMs. PMs are at increased risk of bradycardia.