Determination of zidovudine in human plasma with LC/MS/MS method and application to a bioequivalence Article Abstract

AIM:To develope a sensitive and selective LC/MS/MS method for determination of zidovudine in human plasma and to study the bioequivalences with different formulations. METHODS:Zidovudine and internal standard stavudine were extracted from plasma using liquid-liquid extraction and then separated on a Zorbax Extend C18 column. The mobile phase consisted of methanol-water (70:30, v/v, adjusting pH to 6.0 with 1 % NH4OH), at a flow-rate of 0.5 mL·min-1. A Thermo Finnigan TSQ Quantum Ultra tandem mass spectrometer e- quipped with electrospray ionization source was used as detector and operated in the positive ion mode. Selected reaction monitor using the precursor to produce ion combinations of m/z 268 to 127 and m/z 225 to 127 was taken to quantify zidovudine and the internal standard, respectively. The pharmacokinetic parameters of zidovudine in different formulations were calculated by non-compartment model statistics. RESULTS:The linear calibration curves were obtained in the concentration range of 1.0-2 500 μg·L-1. The lower limit of quantification was 1.0 μg·L-1. The intra-and inter-day relative standard deviation (RSD) over the entire concentration range was less than 8.0 %. Accuracy determined at three concentrations (2.5,50 and 2 000 μg·L-1 for zidovudine) ranged from -1.8 % to 2.8 %. Each plasma sample was chromatographed within 3.6 min. The method was successfully used in bioequivalence study of zidovudine in human plasma after oral administration of 200 mg zidovudine. Pharmacokinetic parameters of zidovudine reference formulation was obtained as follows: tmax was (0.6 ± s 0.3) h, cmax was(l 345 ± 656) μg·L-1, t1/2 was(1.70 ± 0.24) h,AUC0-8 was(l 603 ± 492) μg·h·L-1. For test formulation: tmax was (0.6 ± 0.3) h, cmax was (1 263 ± 637) μg·L-1,t1/2 was(1.60 ± 0.22) h,AUC0-8 was(l 555 ± 361) μg·h· L-1. Calculated with AUC0-8, the bioavailability of two formulations was (100 ± 17) %. The 90 % confidence interval of the individual ratios (test/reference formulation) for cmax and AUC0-8 were within the range of 77.0 % -119.2 % and 90.7 %-107.0 % respectively,supporting the bioequivalent of two formulations. CONCLUSION: LC/MS/MS method is rapid, selective, robust and proved to be suitable for bioequivalence evaluation of different formulations containing zidovudine.