Determination of antrafenine and its main acid metabolite, 2-{[7-(trifluoromethyl)-4-quinolinyl]amino}-benzoic acid, in biological fluids using high-performance liquid chromatography with large volume automatic injection and gas-liquid chromatography with derivative formation.

Specific and sensitive analytical methods have been developed for the measurement of antrafenine and its main acid metabolite, 2-([17-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid (FQB), at therapeutic concentrations in plasma and urine. Following the addition of internal standards (the methyl ester of FQB and 2-([8-(trifluoromethyl)-4-quinolinyl] amino) benzoic acid) the parent drug and the metabolite were extracted from biological material with diethyl ether at a weakly acid pH. Drug extracts were evaporated to dryness prior to chromatographic analysis. Antrafenine was measured by high-performance liquid chromatography using a Spherisorb 5-micrometer ODS column with acetonitrile-0.1 M sodium acetate as the mobile phase. Samples were injected automatically using a 500-microliter injection loop. The detector wavelength was 353 nm corresponding to the maximum UV absorption of both drug and internal standard. The coefficient of variation (C.V.) for the determination of antrafenine concentrations between 5 and 250 ng/ml ranged between 24 and 3%, respectively. The acid metabolite of antrafenine was measured by gas-liquid chromatography with electron-capture detection using a 1 m column packed with 3% OV-225 on Gas-Chrom Q (100-120 mesh) at 240 degrees C and on-column methylation with trimethylphenyl ammonium hydroxide. The C. V. of the method for the analysis of metabolite concentrations between 10 and 500 ng/ml ranged between 3 and 9%, respectively.

Determination of nifuroxazide in biological fluids by automated high-performance liquid chromatography with large-volume injection.

A high-performance liquid chromatographic method for the measurement of nifuroxazide in plasma is described. The technique is based on the single extraction of the drug from buffered plasma with chloroform, using nifuratel as internal standard. The chromatographic system consisted of a 15 cm x 4.6 mm I.D. stainless-steel column packed with Spherisorb ODS, 5 micrometer, and the mobile phase was acetonitrile-orthophosphoric acid (pH 2.5) (30:70). The method was able to measure accurately plasma nifuroxazide concentrations down to 2 ng . ml-1 using 2 ml of sample with no interference from endogenous compounds. The coefficients of variation of the method at 200 and 2 ng . ml-1 were 3% and 15%, respectively, and the calibration graph was linear in this range. The use of automatic injection makes the method suitable for the routine analysis of large numbers of samples.