Plasma determination of the enantiomers of SL 84.0418, a new antihyperglycaemic drug, by HPLC on a chiral alpha 1-AGP column.

SL 84.0418 is a new antihyperglycaemic drug. It is an orally active and selective alpha 2-adrenoceptor antagonist. This molecule, a pyrroloindole derivative, contains an asymmetric center yielding two enantiomers. In order to evaluate the pharmacokinetic profile of both enantiomers following oral administration of the racemate we have developed an HPLC method for their separation and quantification. The liquid-liquid extraction involved three steps with two salting-out procedures at pH 11.5 before and after a back-extraction with 0.005 M H2SO4. The enantiomers were separated by HPLC on a stainless-steel column (100 x 4.0 mm) packed with a chiral alpha 1-acid. The UV response was linear from 1 to 250 ng/ml for both enantiomers. The relative standard deviation (RSD) for reproducibility was below 10.7%. Using quality control samples, precision was found below 7.8% and accuracy was 108%. Extraction recoveries were ca. 60% for both enantiomers and 94% for the internal standard. Column life was brought up to 2 months, which corresponds to about 1,000 injections of biological extract. No guard column was used, but a daily back-flush was carried out. This method is suitable for routine analysis and 30 to 40 plasma samples a day can be processed. This method allows the definition of the pharmacokinetic profile of both enantiomers of SL 84.0418 in human plasma after single oral administration of doses as low as 20 mg of the racemic drug.

Determination of mephenesin in plasma by high-performance liquid chromatography with fluorimetric detection.

A procedure for the determination of the CNS-active muscle-relaxant mephenesin in plasma samples is described. The method involved a single-step extraction with diethyl ether followed by high-performance liquid chromatography separation and fluorimetric detection. Linearity of the detection response was observed between 1 ng/ml, which is the limit of determination, and 500 ng/ml. Inter-day assays, including quality-control samples, performed over a 4-month period, showed the method to be reproducible and precise, and suitable for routine analysis in pharmacokinetic studies.

High-performance liquid chromatographic determination of alfuzosin in biological fluids with fluorimetric detection and large-volume injection.

A high-performance liquid chromatographic method has been developed for the determination of alfuzosin, a new antagonist of alpha 1 post-synaptic adrenergic receptors, in blood, plasma or urine. With fluorimetric detection and the large volume injection technique, the limit of detection in plasma is 0.5-1 ng ml-1, which is sensitive enough for pharmacokinetic studies in man. The calibration graph is linear between 1 and 200 ng ml-1 in blood plasma, with coefficients of variation of 6.2 and 1%, respectively. In urine, the linearity range is 0.05-10 micrograms ml-1; at the lowest concentration, the coefficient of variation is about 10%. A constant plasma/blood concentration ratio (1.25 +/- 0.05) allows the measurement of drug in either fluid. In blood or plasma, alfuzosin is stable at 37 degrees C for 24 h and at -20 degrees C for 6 months. As expected for reversed-phase chromatography, the retention times of alfuzosin and a few of its analogues decrease inversely with the concentration of acetonitrile in the mobile phase. However, as this concentration reaches about 75%, the retention times increase sharply. This U-shaped curve may be explained by interactions of the amino groups with silanol groups of the stationary phase.