title: Stereoselective metabolism of metoprolol: enantioselectivity of alpha-hydroxymetoprolol in plasma and urine.
abstract: Direct stereoselective separation on chiral stationary phase was developed for HPLC analysis of the four stereoisomers of alpha-hydroxymetoprolol in human plasma and urine. Plasma samples were prepared using solid-phase extraction columns and urine samples were prepared by liquid-liquid extraction. The stereoisomers were separated on a Chiralpak AD column at 24 degrees C with fluorescence detection and a mobile phase consisting of a mixture of hexane:ethanol:isopropanol:diethylamine (88:10.2:1.8:0.2) for plasma samples and hexane:ethanol:diethylamine (88:12:0.2) for urine samples. Calibration curves for the individual stereoisomers were linear within the concentration range of 2.0-200 ng/ml plasma or 0.125-25 microg/ml urine. The methods were validated with intra- and interday variations less than 15%. The absolute configuration of the pure stereoisomers were assigned by circular dichroism spectra. The methods were employed to determine the concentrations of alpha-hydroxymetoprolol stereoisomers in a metabolism study of multiple-dose administration of racemic metoprolol to hypertensive patients phenotyped as extensive metabolizers of debrisoquine. We observed stereo-selectivity in the alpha-hydroxymetoprolol formation favoring the new 1'R chiral center from both metoprolol enantiomers (AUC(0-24) (1'R1'S) = 3.02). The similar renal clearances (Cl(R)) of the four stereoisomers demonstrated absence of stereoselectivity in their renal excretion. (-)-(S)-metoprolol was slightly more alpha-hydroxylated than its antipode (AUC(0-24) (2S/2R) = 1.19), suggesting that this pathway is not responsible for plasma accumulation of this enantiomer in humans.
authors.affiliation: Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Paula Macedo
authors.initials: PM
authors.lastname: Cerqueira
authors.forename: Evandro José
authors.initials: EJ
authors.lastname: Cesarino
authors.forename: Carlo
authors.initials: C
authors.lastname: Bertucci
authors.forename: Pierina Sueli
authors.initials: PS
authors.lastname: Bonato
authors.forename: Vera Lucia
authors.initials: VL
authors.lastname: Lanchote
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000097:blood* / Q000737:chemistry / Q000652:urine; D000328:Adult; D000368:Aged; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006801:Humans; D007700:Kinetics; D008790:Metoprolol / Q000031:analogs & derivatives* / Q000097:blood* / Q000737:chemistry* / Q000652:urine; D008875:Middle Aged; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism
chemical_list: D000319:Adrenergic beta-Antagonists; C029504:alpha-hydroxymetoprolol; D008790:Metoprolol