cytochrome P450 2D6 - phenotype, probe drug, metoprolol

Metoprolol/alfa-hydroxymetoprolol metabolic ratio (MR) 3 hours after a single metoprolol dose is used for cytochrome P450 2D6 phenotyping. The aim was to compare cytochrome P450 2D6 metabolic activity after the first metoprolol dose and in steady state. Thirteen adult hypertinsive patients (7 females) in whom an antroduction of the beta-blocker metoprolol was indicated were included. Age (mean ? SD) was 42,8 ? 12,9 years, weight (mean ? SD) was 94,0 ? 25,4 kg. Metoprolol dose was chosen based on clinical grounds on the day of metoprolol first ingestion. Blood samples were drawn after the first dose and at least 2 weeks since metoprolol introduction to ensure steady state. The patients were phenotyped as extensive metabolizers in both periods, after metoprolol first ingestion and in steady state. We observed a significant correlation (rs = 0,8418, P = 0,0003) between the metoprolol/alfa-hydroxymetoprolol MRs.