Abstract: AIM: To establish a simple RP-HPLC method for the determination of niacin in dog plasma and calculate the relative bioavailability and the pharmacokinetic parameters of sustained-release niacin formulation. METHODS: Niacin was extracted from dog plasma with perchloric acid.The RP-HPLC was performed on a Lichrospher C18 column (5 μm, 250 mm×4.6 mm I.D.) with mobile phase of acetonitrile-10 mmol°L^-1 monopotassium phosphate (8∶92, v/v), and the pH of the water phase was adjusted to 4.0 with phosphoric acid at flow rate of 1.0 ml°min-1.Niacin was detected by UV absorbance at 263 nm.Single dose of sustained-release niacin formulation (500 mg)and rapid-release niacin formulation (500 mg)were given to six Beagle dogs.RESULTS: The t1 2, T_max, C_max and MRT of niacin in the sustained release formulation were 1.25±1.15 h, 2.3±0.8 h, 35.3±4.87 mg°L^-1 and 3.45±0.55 h, respectively.The T_max of sustained-release niacin formulation is significantly longer than that of the conventional niacin tablet (P<0.05), the C_max was significantly lower than that of the conventional niacin tablet (P<0.05). CONCLUSION: This method is simple, accurate, sensitive and applicable for pharmacokinetic study of niacin. The relative bioavailability is (40.7±8.6)% in the sustained- release formulation.

Key words: niacin, sustained-release formulation, RP-HPLC, pharmacokinetics, relative bioavailability