Pharmacokinetic evaluation of dipfluzine and its three metabolites in rat plasma using liquid chromatography-mass spectrometry.
A validated LC-MS/MS method to determine the content of dipfluzine (Dip) and its three metabolites (M1, M2, and M5) simultaneously within rat plasma samples was developed. After a single liquid-liquid extraction, the assay was performed by using a C18 column and positive electrospray ionisation mode (ESI) in the multiple reaction monitoring (MRM) mode with transitions of m/z 417.3?167.3, 251.2?165.2, 199.1?121.3, and 183.2?105.1 for Dip, M1, M2, and M5, respectively. Sulfamethoxazole (SMZ) was used as internal standard (IS). The method was linear ranged from 0.5-518, 0.5-524, 1.0-1036, and 0.5-514 ng/ml for Dip, M1, M2, and M5, respectively and all correlation coefficients were greater than 0.9919. The intra- and inter-day precision values obtained were less than 11.5% and the accuracy was between -3.2 and 9.7% for each analyte. The extraction recoveries of their three concentrations for Dip and its three metabolites were all higher than 71.9%. The technique was successfully applied to a pharmacokinetic study of Dip and its metabolites after a single oral administration of Dip (20 mg/kg) to rats. The results indicated that the metabolite formation was rapid and generated M5 as the predominant metabolite, followed by M1 and M2. The maximum plasma concentrations (Cmax) were 59±7, 37±4, 3±0.2, and 55±5 ng/ml; the time to maximum plasma concentration (Tmax) were 65±12, 95±12, 190±25, and 90±0 min and the areas under the concentration-time curves (AUC0??) were 17573±704, 8328±355, 5602±753, and 16101±429 ng min/ml for Dip, M1, M2, and M5, respectively. These results suggested that Dip was extensively metabolized and rapidly absorbed. The half-life (t1/2) of Dip, M1, M2, and M5 were 329±15, 767±75, 2364±434, and 378±36 min, respectively, which indicated that Dip and M5 were eliminated quickly. M2 reached its Tmax later and exhibited a longer t1/2 than the other metabolites, which indicated that there might be some type of flip-flop mechanism at work in the pharmacokinetics of M2.