Stereoselective metabolism of metoprolol: Enantioselectivity of α‐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.

Stereoselective analysis of metoprolol and its metabolites in rat plasma with application to oxidative metabolism

“…Metoprolol (MET) is a selective ␤ 1 -adrenoceptor antagonist used as a racemic mixture for the treatment of hypertension and ischemic heart disease [1][2][3]. The (S)-(−)-MET enantiomer has significantly greater ␤ 1 -adrenergic receptor affinity by 25-fold [4][5][6].…”

Chiral Separation of β-Adrenergic Blockers in Human Plasma by SPE-HPLC

“…It is well known that both the enantiomers of b-adrenergic blockers show different pharmaceutical activities due to their stereo-selective binding with human plasma proteins [18,21]. Therefore, efforts were made to determine the binding concentrations of the reported b-adrenergic blockers, which are given in Table 2.…”

“…Nowadays, solid phase extraction (SPE) is considered as an ideal technique for the extraction of drugs from human plasma as about 80% chromatographers are using this approach [17]. In spite of this, literature survey indicates only one paper describing SPE-Chiral HPLC method for analyses of metoprolol in human plasma [18]. Briefly, the development of SPE-Chiral HPLC method is the need of today for monitoring the concentrations of each enantiomer of b-adrenergic blockers.…”

Análise enantiosseletiva de fármacos: contribuições da cromatografia líquida de alta eficiência e eletroforese capilar

“…As referências já citadas nesse texto 44,48,52,[89][90][91][92][93][94][95]100,104,110 e algumas outras publicações recentes [121][122][123][124] demostram o grande envolvimento desses grupos na análise enantiosseletiva de fármacos e metabólitos em materiais biológi-cos. Como as análises são feitas em matrizes biológicas complexas e analitos presentes em quantidades muito baixas, também estão sendo desenvolvidos e validados novos procedimentos de preparação da amostra como, por ex., a microextração em fase sóli-da 110 . Graças a esses métodos desenvolvidos, vários estudos de disposição cinética estão sendo realizados, possibilitando estabelecer a influência de várias doenças e aspectos genéticos na disposição cinética de fármacos quirais, sendo citados apenas os mais recentes [125][126][127][128][129] . Um outro grupo, do Instituto de Química da Universidade Federal de São Carlos, atua no desenvolvimento de novas fases estacionárias quirais e modos de separação e, mais recentemente, em aplicações na análise de fármacos quirais em materiais biológicos.…”