Stereoselective metabolism of metoprolol: enantioselectivity of alpha-hydroxymetoprolol in plasma and urine.
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.
Cerqueira
Paula Macedo
PM
Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, SP, Brazil.
Cesarino
Evandro José
EJ
Bertucci
Carlo
C
Bonato
Pierina Sueli
PS
Lanchote
Vera Lucia
VL
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
D000319:Adrenergic beta-Antagonists; C029504:alpha-hydroxymetoprolol; D008790:Metoprolol