Chiral separation of the enantiomers of metoprolol and its metabolites by high performance liquid chromatography

Development of a sensitive and rapid method for quantitation of (S)-(-)- and (R)-(+)-metoprolol in human plasma by chiral LC-ESI-MS/MS

A selective, sensitive and high throughput liquid chromatography-tandem mass spectrometry (LC–ESI–MS/MS) method has been developed for separation and quantification of metoprolol enantiomers on a chiral Lux Amylose-2 (250 mm×4.6 mm, 5 μm) column. Solid phase extraction of (S)-(−)- and (R)-(+)-metoprolol and rac-metoprolol-d6 as an internal standard (IS) was achieved on Lichrosep DVB HL cartridges employing 200 μL human plasma. Both the analytes were chromatographically separated with a resolution factor of 2.24 using 15 mM ammonium acetate in water, pH 5.0 and 0.1% (v/v) diethyl amine in acetonitrile (50:50, v/v) as the mobile phase within 7.0 min. The precursor→product ion transitions for the enantiomers and IS were monitored in the multiple reaction monitoring and positive ionization mode. The method was validated over the concentration range of 0.500–500 ng/mL for both the enantiomers. Matrix effect was assessed by post-column analyte infusion experiment and the mean extraction recovery was greater than 94.0% for both the enantiomers at all quality control levels. The stability of analytes was evaluated in plasma and whole blood under different storage conditions. The method was successfully applied to a clinical study in 14 healthy volunteers after oral administration of 200 mg metoprolol tablet under fasting conditions. The assay reproducibility is shown by reanalysis of 68 incurred samples. The suitability of the developed method was assessed in comparison with different chromatographic methods developed for stereoselective analysis of metoprolol in biological matrices.

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.

Enantioselective determination of metoprolol acidic metabolite in plasma and urine using liquid chromatography chiral columns: applications to pharmacokinetics

Enantioselective separations on chiral stationary phases with or without derivatization were developed and compared for the HPLC analysis of (+)-(R)- and (-)-(S)-metoprolol acidic metabolite in human plasma and urine. The enantiomers were analysed in plasma and urine without derivatization on a Chiralcel OD-R column, and in urine after derivatization using methanol in acidic medium on a Chiralcel OD-H column. The quantitation limits were 17 ng of each enantiomer/ml plasma and 0.5 microgram of each enantiomer/ml urine using both methods. The confident limits show that the methods are compatible with pharmacokinetic investigations of the enantioselective metabolism of metoprolol. The methods were employed in a metabolism study of racemic metoprolol administered to a patient phenotyped as an extensive metabolizer of debrisoquine. The enantiomeric ratio (+)-(R)/(-)-(S)-acid metabolite was 1.1 for plasma and 1.2 for urine. Clearances were 0.41 and 0.25 l/h/kg, respectively, for the (+)-(R)- and (-)-(S)-enantiomers. The correlation coefficients between the urine concentrations of the acid metabolite enantiomers obtained by the two methods were >0.99. The two methods demonstrated interchangeable application to pharmacokinetics.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Enantioselective determination of metoprolol and major metabolites in human urine by capillary electrophoresis

The enantiomeric separation of metoprolol and its metabolites in human urine was undertaken using capillary electrophoresis (CE). Resolution of the enantiomers was achieved using carboxymethyl-beta-cyclodextrin (CM-beta-CD) as the chiral selector. A 100-mM acetate buffer (pH 4.0) containing 5% 2-propanol and 10 mM CM-beta-CD resulted in the optimum separation of the metoprolol enantiomers and its acidic metabolite in human urine. Following a single metoprolol oral administration of 100 mg racemic metoprolol tartrate, stereoselective pharmacokinetic analysis showed that urinary acidic metabolite 3 of metoprolol accounted for 62.3% of the dose with an R/S ratio of 1.23 and urinary unchanged metoprolol 1 accounted for 6.3% of the dose with an R/S ratio of 0.72.