Two different spectrophotometric determinations of potential anticancer drug and its toxic metabolite

Flutamide is a hormone therapy used for men with advanced prostate cancer. Flutamide is highly susceptible to hydrolysis with the production of 3-(trifluoromethyl)aniline, which is reported to be one of its toxic metabolites, impurities and related substances according to BP and USP. Flutamide was found to be stable when exposed to oxidation by 30% hydrogen peroxide and direct sunlight for up to 4h. Two accurate and sensitive spectrophotometric methods were used for determination of flutamide in bulk and in pharmaceutical formulations. Method (I) is the area under curve (AUC) spectrophotometric method that depends on measuring the AUC in the wavelength ranges of 275-305 nm and 350-380nm and using Cramer's rule. The linearity range was found to be 1-35 μg/mL and 0.5-16 μg/mL for the drug and the degradate, respectively. In method (II), combination of the isoabsorptive and dual wavelength spectrophotometric methods was used for resolving the binary mixture. The absorbance at 249.2 nm (λiso) was used for determination of total mixture concentration, while the difference in absorbance between 232 nm and 341.2 nm was used for measuring the drug concentration. By subtraction, the degradate concentration was obtained. Beer's law was obeyed in the range of 2-35 μg/mL and 0.5-20 μg/mL for the drug and its degradate, respectively. The two methods were validated according to USP guidelines and were applied for determination of the drug in its pharmaceutical dosage form. Moreover AUC method was used for the kinetic study of the hydrolytic degradation of flutamide. The kinetic degradation of flutamide was found to follow pseudo-first order kinetics and is pH and temperature dependent. Activation energy, kinetic rate constants and t1/2 at different temperatures and pH values were calculated.