Quantitative Analyses Of Nisoldipine And Rasagiline In Human Plasma And Their Applications

BACKGROUND Nisoldipine is a second generation of dihydropyridine calcium antagonist which has a selective arteriolar vasodilation but shows negligible effects on the other vessels and myocardium. Nisoldipine is rapidly absorbed by the gastrointestinal tract, whereas its oral bioavailability is very low (3.9% - 8.4%) due to a significant first-pass effect in the liver. Rasagiline is a potent selective irreversible inhibitor of monoamine oxidase type B and has been used for the treatment of idiopathic Parkinson's disease both as monotherapy in early disease and as adjunctive therapy for levodopa in advanced disease. Rasagiline is rapidly absorbed by the gastrointestinal tract and readily crosses the blood－brain barrier. Due to extensive metabolism and wide distribution to tissues, the plasma concentration of rasagiline is very low in humans. The challenge arise from low plasma concentration, results in difficulty in studying the pharmacokinetics of these agents.OBJECTIVE To develop and validate two sensitive, rapid and specific liquid chromatographic－tandem mass spectrometric methods forrespectively determination of nisoldipine and rasagiline in human plasma and application to the clinical pharmacokinetics of low dose.METHOD For determination of the plasma concentration of nisoldipine, an aliquot of 500μL plasma was extracted with n-hexane－dichlormethane - isopropanol (20: 10: 1, v/v/v), then separated on a Zorbax Eclipse XDB C₈ column using acetonitrile－water－formic acid (90: 10: 0.1, v/v/v) as the mobile phase. The triple quadrupole mass spectrometry was applied via an atmospheric pressure chemical ionization (APCI) source for detection. Quantitation was performed using multiple reaction monitoring(MRM) of the transitions of m/z 389.2→m/z 315.2 and m/z 419.2→m/z343.2 for nisoldipine and the internal standard nimodipine, respectively.For determination of the plasma concentration of rasagiline, an aliquotof 500μL plasma was treated with 100μL of pH 7 phosphate buffer andextracted with n-hexane－dichlormethane－isopropanol (20: 10: 1, v/v/v), then separated on a Zorbax Extend C₁₈ column using acetonitrile－5 mM ammonium acetate - acetic acid (40: 60: 0.05, v/v/v) as the mobile phase. The API 4000 triple quadrupole mass spectrometer was operated in multiple reaction monitoring mode via positive electrospray ionizationinterface using the transitions m/z 172.1→m/z (117.1+115.1) forrasagiline, and m/z 166.0→m/z 148.0 for the internal standard.RESULTS The linear calibration curves were obtained in the concentration range of 0.020－8.00 ng·mL^-1 for nisoldipine. The lowerlimit of quantification was 0.020 ng·mL^-1. The intra-day and inter-day precision (RSD) over the entire concentration range was less than 7.6%. The accuracy was in the range of -3.8% to 0.1% in terms of relative error. Each plasma sample was chromatographed within 3.0 min. More than 150 plasma samples could be assayed within each day. Following a single oral dose of 10 mg nisoldipine test formulation, 90% confidence interval forAUC_{0－24 h} and C_max were 96.0%－115% and 71.0%－97.5%, respectively.Thus the test formulation of nisoldipine was considered bioequivalent to the reference formulation according to both the rate and the extent of absorption.The linear calibration curves were obtained in the concentration rangeof 0.020 - 50.0 ng·mL^-1 for rasagiline. The lower limit of quantificationwas 0.020 ng·mL^-1. The intra-day and inter-day relative standard deviationover the entire concentration range was less than 11.2%. The accuracy was in the range of 0.1% to 6.4% in terms of relative error. Each plasma sample was chromatographed within 3.6 min. The method was successfully used in the clinical pharmacokinetic study of rasagiline mesylate tablet. After single oral doses of 1, 2 and 5 mg rasagiline to healthy volunteers,respectively, the pharmacokinetic parameters (AUC_{0－24 h} and C_max) ofrasagiline were increased inpro dose. The main pharmacokinetic parameters for rasagiline exhibited significant individual differences.CONCLUSION The validated liquid chromatographic－tandem mass spectrometric methods were sensitive, selective, rapid and suitable for evaluating the clinical pharmacokinetics of nisoldipine and rasagiline in humans.