Metoprolol has been used during pregnancy for the treatment of maternal hypetension and tachycardia. The main route of elimination is oxidation via cytochrome P450 2D6 to 2 metabolites (especial alfa-hydroxymetoprolol). The serum half-lives determined during the 3rd trimester and repeated 3-5 months after delivery were reported similar, but peak levels during pregnancy were only 20-40% of those measured later.