Spectrofluorimetric determination of 3-methylflavone-8-carboxylic acid, the main active metabolite of flavoxate hydrochloride in human urine

A simple, sensitive and selective spectrofluorimetric method has been developed for the determination of 3-methylflavone-8-carboxylic acid as the main active metabolite of flavoxate hydrochloride in human urine. The proposed method was based on the measurement of the native fluorescence of the metabolite in methanol at an emission wavelength 390 nm, upon excitation at 338 nm. Moreover, the urinary excretion pattern has been calculated using the proposed method. Taking the advantage that 3-methylflavone-8-carboxylic acid is also the alkaline degradate, the proposed method was applied to in vitro determination of flavoxate hydrochloride in tablets dosage form via the measurement of its corresponding degradate. The method was validated in accordance with the ICH requirements and statistically compared to the official method with no significant difference in performance.

Development of a high-performance liquid chromatographic method for bioequivalence study of flavoxate tablets

An improved HPLC method was developed for the concentration determination of the metabolite of flavoxate, 3-methyl-flavone-8-carboxylic acid (MFCA), in plasma in an attempt to compare two flavoxate tablet formulations. This HPLC method was validated by examining the precision and the accuracy for inter-day and intra-day runs in a linear concentration range of 0.1-24 microg/ml. The coefficients of variation (C.V.) of inter-day and intra-day assays were 0.24-7.18% and 0.06-5.70%, respectively. The standard errors of mean (S.E.M.) were -0.004-8.68% and -2.52-4.86% for inter-day and intra-day assays, respectively. Bioequivalence of the two formulations was determined on 12 normal healthy male volunteers in a single-dose, two-period, two-sequence, two-treatment crossover study. MFCA plasma concentrations were analyzed with this validated HPLC method. The normal pivotal parameters, AUC(0-last), AUC(0-inf) and Cmax, were calculated and compared using the SAS General Linear Model computer program. The two one-sided t distribution test was also performed, as well as the 90% confidence-interval method, for the mean difference of the three pivotal parameters. The results suggest that these two flavoxate tablet formulations are non-bioequivalent when orally administered in a 400-mg dose of two tablets. This result was consistent with the in vitro dissolution of these two formulations.

Determination of 3-methylflavone-8-carboxylic acid, the main metabolite of flavoxate, in human urine by capillary electrophoresis with direct injection

The effects of tetraalkylammonium salts and sodium dodecyl sulphate on the migration behaviour of human urinary components and other negatively charged or neutral solutes were investigated. The sulphate acted mainly on hydrophobic and positively charged substances, whereas the ammonium salts acted mainly on negatively charged solutes. By choosing the components of the eluent carefully, the free and conjugate forms of 3-methylflavone-8-carboxylic acid (MFA) in human urine, the major metabolites of flavoxate, could be simultaneously determined without pretreatment, using fenprofen as an internal standard. The calibration curve of MFA was linear in the range 1-50 micrograms/ml and the detection limit was 0.2 microgram/ml, which covered the urine levels encountered in pharmacokinetic studies. The intra-day and inter-day precisions of the method, expressed as the relative standard deviation, were less than 2 and 3%, respectively. This method was successfully applied to an excretion study of MFA in eight healthy volunteers, and the results were in agreement with data in the literature obtained by gas chromatography.