ISOCRATIC HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF THIACETAZONE BY DIRECT-INJECTION OF PLASMA INTO AN INTERNAL SURFACE REVERSED-PHASE COLUMN

This report describes the determination of thiacetazone in human and r at plasma by direct-injection high-performance liquid chromatography ( HPLC). Plasma filtrate (50 mu l) was injected directly into the intern al surface reversed-phase (ISRP) mixed-functional phenyl column (Capce ll Pak, 50x4.6 mm, 5 mu m) and eluted with an aqueous mobile phase con taining 7.5% acetonitrile at a flow-rate of 1 ml/min. With UV detectio n at 322 nm, thiacetazone eluted at 11.0 min whereas endogenous interf erences eluted before 5 min. The lower detection limit for a 50-mu l s ample at a signal-to-noise ratio of 5 was 63 ng/ml, which was several hundred fold lower than its cytotoxic concentrations determined from i n vitro cell line studies. At a concentration range of 0.17 to 2.7 mu g/ml, the recovery of thiacetazone was 98.0+/-4.4% (mean+/-S.D.). The intra- and inter-day coefficients of variation were 3.0+/-1.4% and 4.2 +/-2.1%, respectively. This method was successfully applied to study t he pharmacokinetics of thiacetazone in rats. The direct injection meth od is simple, requires small sample volume and does not require sample extraction, internal standard, or gradient elution.