Fig. 1

Principal pathways of metoprolol metabolism. Metoprolol is primarily metabolized to α-hydroxymetoprolol (HM) and O-demethylmetoprolol (DM) by hepatic CYP2D6 and to a lesser extent CYP3A4. O-demethylmetoprolol (DM) subsequently undergoes rapid oxidation to form metoprolol acid (MA)