To develop a new method for quantifying fluoconazole in human plasma and to compare the bioavailability of two fluconazole capsule formulations, an open, randomized, two-period crossover study with a one-week washout interval was conducted in 24 healthy volunteers. Plasma samples were obtained up to 168 hours after drug administration and the serum fluconazole concentrations were analyzed using electrospray tandem mass spectrometry coupled to liquid chromatography using multiple reaction monitoring mode. The pharmacokinetic parameters obtained for fluconazole after the administration of each formulation included the Area under the curve (AUC)((0-168h)), AUC(-∞), Cmax, Cmax/AUC((0-168h)), Tmax, elimination rate constant (Ke), and half- life (T(1/2)). Within- and between-run imprecision was less than 2.3% and 8.2%, respectively. Inaccuracy within and between runs was -1.5% and -9.7%, respectively. The pharmacokinetic parameters for bioequivalence showed a normal distribution, and the variance of AUC((0-168h)), AUC((0-∞)), and Cmax were homoscedastic. The geometric mean for the Fluconal/Zoltec (Fluconal; Libbs Farmaceutica Ltda, Sao Paulo, Brazil; Zoltec; Laboratorios Pfizer Ltda., Sao Paulo, Brazil) individual percent ratio was 94.9% for AUC((0- 168h)), 94.7% for AUC((0-∞)), 80.1% for Cmax, 102.6% for Ke, 97.5% for T(1/2), and 0.93 for Tmax (arithmetic mean of individual differences). We have developed a method in which liquid chromatography is coupled with electrospray tandem mass spectrometry to improve the pharmacokinetic analysis of fluconazole. Because the 90% CI AUC is within the interval proposed for the Food and Drug Administration, we concluded that Fluconal is bioequivalent to Zoltec in terms of absorption. The CV was 27.5% for the Cmax parameter, indicating that fluconazole's absorption rate is highly variable. The European Union Regulatory Agency accepts an interval of 70-143 %, and because the 90% CI for Cmax is within the interval proposed for the European Union agency, we conclude that Fluconal is bioequivalent to Zoltec for the rate of absorption.
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