SIMULTANEOUS MEASUREMENT OF NICOTINIC-ACID AND ITS MAJOR METABOLITE, NICOTINURIC ACID IN URINE USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY - APPLICATION OF SOLID-LIQUID EXTRACTION

The concentrations of nicotinic acid (NiAc) and nicotinuric acid (NiUAc), a major metabolite of NiAc, were simultaneously determined in urine using solid-phase extraction (cation-exchange extraction) and reversed-phase high-performance liquid chromatography with ultraviolet detection. The intra- and inter-day precision studies showed good reproducibilities: the coefficients of variations were less than 8.1% for NiAc and 8.8% for NiUAc. The calibration curves were linear (r(2)>0.9934) in the concentration range 10-1000 mu g/ml. The removal of endogenous interferences in urine by solid-phase extraction presented here is superior to the pretreatment protocols reported previously by other workers. The method was used in a preliminary pharmacokinetic study in rats after intravenous administration of NiAc (5 and 15 mg/kg).