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Objective: To develop sensitive and specific LC-MS/MS methods for determination of nicotinic acid （NA）, nicotinuric acid （NUA） and nicotin- amide （NAM） in human plasma and to study the clinical pharmacokinetics of nicotinic acid sustain release capsules.Method: To simultaneous determine nicotinic acid, nicotinuric acid and nicotinamide by a liquid chromatographic?tandem mass spectrometric method. NA, NUA, NAM and the internal standard, paracetamol, were isolated from 100μL plasma by protein precipitation with methanol, and then chromatographed on a Venusil ASB C18 column （150 mm×4.6 i.d., 5μm）, using methanol?water?acetic acid?ammonia solution （30: 70: 0.02: 0.002, v/v/v/v） as the mobile phase. The detection was performed on a tandem mass spectrometer equipped with an atmospheric pressure chemical ionization source. Detection was performed by atmospheric pressure chemical ionization （APCI） in multiple reaction monitoring （MRM） mode using the transitions m/z 124→m/z 80 for NA, m/z 181→m/z 135 for NUA, m/z 123→m/z （78 + 80） for NAM and m/z 152→m/z 110 for paracetamol （internal standard）.Result: Linear calibration curves of NA, NUA and NAM were obtained in the concentration ranges of 2.00?1000, 2.00?1000, and 15.0?1000 ng/mL, respectively. This method was successfully applied for the pharmacokinetic study of nicotinic acid sustained release capsules. Thirty volunteers received after a single oral dose of 500, 750, 1000 mg nicotinic acid. Maximal nicotinic acid plasma level was observed after （2.75±0.589） h, （2.65±1.16） h, （3.95±1.74） h, respectively; Cmax was （767±879）μg·L-1, （609±642）μg·L-1, （297±377）μg·L-1, respectively; T1/2 was （6.07±2.35） h, （8.43±4.40） h, （13.0±10.9） h, respectively; AUC(0-24 was （1677±1223）μg·h·L-1, （1195±572）μg·h·L-1, （628±358）μg·h·L-1, respectively; AUC0-∞ was （1751±1195）μg·h·L-1, （1301±572）μg·h·L-1, （796±352）μg·h·L-1. Maximal nicotinuric acid plasma level was observed after （2.70±0.675） h, （2.70±0.715） h, （3.10±0.966） h, respectively; Cmax was （1694±1201）μg·L-1, （1011±436）μg·L-1, （577±302）μg·L-1, respectively; T1/2 was （2.87±2.03） h, （2.87±1.29） h, （2.74±1.90） h, respectively; AUC(0-24 was （5722±4538）μg·h·L-1, （2743±1201）μg·h·L-1, （1403±655）μg·h·L-1, respectively; AUC0-∞ was （5748±4520）μg·h·L-1, （2754±1208）μg·h·L-1, （1413±661）μg·h·L-1. Maximal nicotinamide plasma level was observed after （4.65±0.709） h, （5.10±1.87） h, （5.70±2.08） h, respectively; Cmax was （513±225）μg·L-1, （302±98.0）μg·L-1, （223±58.8）μg·L-1, respectively; T1/2 was （6.69±4.26） h, （16.3±14.8） h, （8.05±5.52） h, respectively; AUC(0-24 was （4121±1621）μg·h·L-1, （2674±1133）μg·h·L-1, （1618±665）μg·h·L-1, respectively; AUC0-∞ was （4727±1631）μg·h·L-1, （4230±2251）μg·h·L-1, （1961±985）μg·h·L-1 respectively.Ten volunteers received after multiple oral dose of 1000 mg nicotinic acid. Maximal nicotinic acid plasma level was observed after （2.75±0.635） h, Cmax was （1901±1133）μg·L-1, T1/2 was （10.5±8.26） h, AUC(0-24 was （3470±1977）μg·h·L-1, AUC0-∞ was （3589±1958）μg·h·L-1, AUCss was （3329±1974）μg·h·L-1; Maximal nicotinruic acid plasma level was observed after （2.77±1.11） h, Cmax was （2052±929）μg·L-1, Tmax was （3.25±0.890） h, AUC(0-24 was （7205±4348）μg·h·L-1, AUC0-∞ was （7217±4353）μg·h·L-1, AUCss was （7131±4312）μg·h·L-1; Maximal nicotinamide plasma level was observed after （12.4±8.11） h, Cmax was （558±264）μg·L-1, Tmax was （4.85±1.55） h, AUC(0-24 was （6312±2884）μg·h·L-1, AUC0-∞ was （8772±3795）μg·h·L-1, AUCss was （4111±1963）μg·h·L-1.Conclusion: A sensitive, rapid and convenient LC?MS/MS method was developed and validated for determination of NA, NUA and NAM in human plasma. The method was proved suitable for the pharmacokinetic study of nicotinic acid sustained release capsules.
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