Metoprolol apparent oral clearance of extensive and intermediate metabolizers during pregnancy and postpartum. Subjects were classified as extensive metabolizers (EMs) if they had 2 fully functional CYP2D6 alleles (*1 and *35) or 2 reduced-activity alleles (*9, *10, *17, or *41) or 1 fully functional allele together with 1 reduced-activity allele; intermediate metabolizers (IMs) if they had 1 nonfunctional CYP2D6 allele (*3, *4, *5, or *6) with either 1 functional allele or 1 reduced-activity allele; and poor metabolizers (PMs) if they carried 2 nonfunctional CYP2D6 alleles. The lines indicate mean values; closed circles indicate EMs; and open circles indicate IMs. Statistical significance (P < .05) when compared with postpartum is indicated by an asterisk.