Determination of ranolazine and its pharmacokinetics in dog by LC-MS

Aim: To develop an LC-MS method for the determination of ranolazine concentration in dog plasma and study pharmacokinetics of ranolazine in Beagle dog. Method: 20 μl plasma was mixed 10 min with 300 μl acetonitrile. After being centrifuged, 10 μl supernatant was injected into a Shim-pack C₁₈ 150 mm × 2.0 mm column. The mobile phase consisted of acetonitrile-0.05% acetic acid (60:40, v/v) at flow rate of 0.2 ml/min. The elute from the HPLC column was plumbed directly into APCI probe. Analysis in the mass spectrometer was operated in the selected-ion monitoring model. The mass spectrometers was operated in SIM m/z 428 for ranolazine and 344 for DDPH (as internal standard). Dog blood samples were obtained after oral and intravenous administration of 25 mg/kg respectively. Ranolazine concentrations in plasma were determined and pharamcokinetic parameters were also estimated. Result: Recoveries of ranolazine at 0.16, 0.62 and 10.0 μg/ml were 90.8, 87.0 and 79.3% respectively. The standard curve was linear in the range of 0.039 ∼ 10.00 μg/ml. The relative standard derivation of intra-day and inter-day was smaller than 10%. Terminal phase t_1/2 were estimated to be 7.31 and 5.67 hours after ig and iv of 25 mg/kg ranolazine. Peak concentration (4.32 ± 1.25 μg/ml) occurred at 1.0 ± 0.6 hours after ig. Absolute bioavailability was (72.6 ± 15.6)% for ig. Conclusion: The bioanalytical method of LC-MS is suitable for pharmacokinetic study of ranolazine. Oral absorption of ranolazine occurs rapidly and completely in dogs.