Simultaneous determination of niacin and its metabolites--nicotinamide, nicotinuric acid and N-methyl-2-pyridone-5-carboxamide--in human plasma by LC-MS/MS and its application to a human pharmacokinetic study.

An LC-MS/MS method for the simultaneous quantitation of niacin (NA) and its metabolites, i.e. nicotinamide (NAM), nicotinuric acid (NUA) and N-methyl-2-pyridone-5-carboxamide (2-Pyr), in human plasma (1 mL) was developed and validated using nevirapine as an internal standard (IS). Extraction of the NA and its metabolites along with the IS from human plasma was accomplished using a simple liquid-liquid extraction. The chromatographic separation of NA, NAM, NUA, 2-Pyr and IS was achieved on a Hypersil-BDS column (150 x 4.6 mm, 5 microm) column using a mobile phase consisting of 0.1% formic acid : acetonitrile (20:80 v/v) at a flow rate of 1 mL/min. The total run time of analysis was 2 min and elution of NA, NAM, NUA, 2-Pyr and IS occurred at 1.37, 1.46, 1.40, 1.06 and 1.27 min, respectively. A detailed validation of the method was performed as per the FDA guidelines and the standard curves were found to be linear in the range of 100-20000 ng/mL for NA; 10-1600 ng/mL for NUA and NAM and 50-5000 ng/mL for 2-Pyr with mean correlation coefficient of ≥ 0.99 for each analyte. The method was sensitive, specific, precise, accurate and suitable for bioequivalence and pharmacokinetic studies. The developed assay method was successfully applied to a pharmacokinetic study in humans.