Development and validation of a stability-indicating RP-HPLC method for analysis of doxofylline in human serum. Application of the method to a pharmacokinetic study

A simple, isocratic, stability-indicating reversed-phase high-performance liquid chromatographic (RP-HPLC) method has been developed for determination of doxofylline in human serum. The method employs precipitation for isolation and sample concentration, followed by reversed-phase liquid chromatographic analysis with ultraviolet (UV) detection at 275 nm. Analytes were extracted from serum with 400 µL methanol. Samples containing the internal standard (metronidazole) and doxofylline were chromatographed on a C18 column with 18:82 acetonitrile–phosphate buffer (12.5 mM potassium dihydrogen orthophosphate, pH 3.0) as mobile phase at a flow rate of 1 mL min.1. The retention times of doxofylline and metronidazole were 7.54 min and 4.36 min, respectively. The intra-day and inter-day coefficients of variation and the error of the assay were <15%. The calibration plot was linear for concentrations in the range of 0.025 to 25 µg mL.1. The extraction recovery of doxofylline was >95%. The validated method was applied to a pharmacokinetic study of doxofylline in human serum after administration of a single doxofylline tablet (400 mg). The method is ideally suited to estimation of the drug for pharmacokinetic studies on human volunteers after oral administration of doxofylline.