High-performance liquid chromatography of deacetylmetipranolol in plasma.

A sensitive high-performance liquid chromatographic method with electro-chemical detection is developed for the determination of deacetylmetipranolol (DMP), an active metabolite of beta-sympatholytic drug metipranolol (MP). DMP is extracted from the plasma after basifying with dichloromethane. After evaporation, the residue is reconstituted in the mobile phase, injected onto the reversed-phase ODS column and chromatographed at 50 degrees C. The sensitivity of the method is 2 ng of DMP in 1 ml plasma. Pindolol, another beta-blocking agent is used as internal standard. The method is used for a pharmacokinetic investigation of MP in healthy volunteers and in the patients with liver cirrhosis.

Direct high-performance liquid chromatographic determination of the enantiomeric purity of levodopa and methyldopa: comparison with pharmacopoeial polarimetric methods.

Chiral high-performance liquid chromatography was employed for determination of the enantiomeric purity of levodopa and methyldopa. The determination of D-DOPA in levodopa was accomplished using a chiral ligand-exchange chromatograpy with an ordinary C18 column and a chiral mobile phase containing N,N-dimethyl-L-phenylalanine and Cu(II) acetate or by means of LC on a teicoplanin column in conjunction with ethanol-water (65:35, v/v). Both methods gave good performance, however, the latter was faster and more convenient and suitable for routine analyses. For the determination of D-methyldopa a LC method based on the use of a teicoplanin column in polar organic mode with methanol-acetic acid-triethylamine (1,000:0.05:0.05, v/v/v) mobile phase was developed. The precision, accuracy, linearity and selectivity were satisfactory. In comparison with pharmacopoeial polarimetric methods (according to the European Pharmacopoeia and the Pharmacopoea Bohemoslovaca), the LC methods proved to be much more sensitive giving detection limits 0.04% of D-DOPA and 0.3% of D-methyldopa.

LC determination of the enantiomeric purity of levamisole using stationary phase with bonded naphthylethylcarbamoylated-beta-cyclodextrin.

A direct enantioselective high-performance liquid chromatography was employed successfully for determination of the enantiomeric purity of levamisole. The elaborated method used S-naphthylethylcarbamoylated beta-cyclodextrin stationary phase in reversed-phase mode. The optimized mobile phase composition was acetonitrile-0.5% triethylammonium acetate buffer, pH 5.0 (2:8, v/v). Linearity, precision, accuracy, and the quantitation limit were determined. The method proved to be capable of determining 0.05% (w/w) of dexamisole (the enantiomeric impurity) contrary to the pharmacopoeial optical rotation measurement, in which only amounts of dexamisole higher than 2.2% (w/w) caused the test to fail. The enantiomeric purity of three different levamisole substances and levamisole tablets was assessed with the use of the method. The content of dexamisole impurity was found to be in the range 0.66-1.60% (w/w).

Disposition kinetics and concentration-effect relationship of metipranolol in patients with cirrhosis and healthy subjects.

The disposition kinetics and heart rate reducing effect of deacetylmetipranolol (DMP), the active form of the beta-adrenoreceptor blocking agent metipranolol (MP), administered as a single 40 mg oral dose have been compared in 6 patients with cirrhosis and 6 healthy volunteers. The mean maximal DMP concentration was significantly higher and the time to reach the peak level shorter in the patients compared to the healthy subjects. There was also a significantly higher AUC of DMP, a shorter half-life of the rapid phase of the decline in DMP concentrations, a smaller central compartment and lower apparent DMP clearance in patients. A correlation with the albumin level was observed in cirrhotics for individual values of apparent DMP clearance (r = 0.92) and AUC (r = -0.89). The maximal reduction in heart rate was recorded in patients at plasma DMP levels which were already significantly lower than the peak levels. Median inhibitory concentrations (IC50) and maximum possible heart rate reductions (delta HRmax), obtained by fitting individual plots of the plasma DMP concentration-effect relationship to the inhibitory Emax model in the postdistributional phase of DMP disposition were significantly higher in cirrhotics than in healthy subjects. It is conjectured that down-regulation of adrenoreceptors due to chronic sympathetic activation in hepatic cirrhosis contributes to decreased sensitivity to the reduction in heart rate following a single dose of the beta-blocker.