Determination Of Extended-release Niacin Formulation By RP-HPLC In Dog's Plasma And Its Pharmacokinetics Study

ObjectiveTo establish a simple RP—HPLC method for the determination of ni-acin in dogs plasma and calculate the pharmacokinetics parameters and the relative bioavailability of extended — release(ER) niacin formulation.Methods1. Chromatographic conditionsNiacin was measured by HPLC using DIKMA Diamonsil^TMC₁₈Column (200mm × 4. 6mm,5μm) as stationary phase and methanol — water — acetic acid(20:80:0.1)(V : V : V) as mobile phase. The UV detector wavelength was 254nm, and the flow rate was 1.0ml/min.2. Drug administration and sample collection8 Beagle dogs were divided into two groups at random . One group was given ER niacin tablet 500mg(Test) ,and the other was given con— ventional niacin tablets 500mg(Reference). Blood samples (1. 0ml) were taken just before drug ingestion and at 0. 5,1. 0, 1. 5,2. 0, 2. 5,3. 0, 3. 5, 4. 0, 5. 0,7. 0,11. 0 and 24. 0h after administration of the drug, then immediately transferred into heparinized tubes and centrifuged for 10 min at 3500rpm. The supernatants were pipetted into another clean centrifuged tube and stored at — 20℃ until being assayed. After a washout period of 7 days,a crossover test was repeated in the same manner.3. Pretreatment of blood sampleTo a 1. 5 ml centrifuged tube,200^1 of blood plasma,40/Ltl of internal standard solution and 400jud alcohol were added. Each tube was mixed thoroughly by vortexing for 1 min. After centrifugation for 5 min at 10900rpm, the supernatants were filtered through a 0. 45jnm filter and 20}j.\ of the sample was injected into the analytical column. Blank plasma sample was prepared in the same way as a control.4. Data analysisThe pharmacokinetics parameters were calculated by using the "3p97" Pharmacokinetics Program (Chinese Society of Mathematic pharmacology, Beijing, China, 1997) .Results1. Identification of determination of niacin in plasma1. 1 Chromatograms of niacinThe retention time of niacin is (4. 47 + 0. 03) min and retention time of the internal standard is (11. 52 + 0. 03) min. Plasma endogenous materials has no interference with -the content of niacin.1. 2 Standard curveA series of plasma with different concentrations of niacin at 150, 100,50,25,12. 5,6. 25,3. 125,1. 56,0. 78 /Mg/ml were mixed with 40/llL of internal standard solution and treated as described in the section of "Pre-treatment of plasma sample". A standard curve was derived by using the ratio (Y) (peak area niacin versus peak area internal standard ) against the concentration of niacin(X) . The regression equation is :Y = 0. 0153X + O.OO66,(r=O. 9993,n = 8). The results showed that the curve is linear over the concentration range between 0. 78 and 150 jug/ml . The detection limit of niacin is 0. 78/^g/ml .1. 3 Validation studyThe intra— and inter—day precision were 90%. Stability experiment showed that niacin in plasma stored at — 20°C was stable.2. Pharmacokinetics analysisA two—compartment model was adopted in niacin plasma concen — tration — time data analysis. The main pharmacokinetics parameters of Test and Reference tablets were as following : Cmax( jMg/ml ) were 15. 54 + 3.47 and 107.45 ±17.02;Tmax( h)were 1.84 +0. 28 and 1. 01+ 0.09;AUC0₂4(^g. h/ml ) were 169. 22 ±31. 85 and 414. 82 ±29. 64, respectively. The relative bioavailability of extended — release (ER)niacin tablet was (40.79 ±1.07)%.ConclusionThis method is simple,accurate,sensitive and applicable for pharma-cokinetic study of niacin. The Tmax of ER niacin tablet is significantly longer than that of the conventional niacin tablet(P