Stability study of flutamide in solid state and in aqueous solution.

A high-performance liquid chromatography (HPLC) assay has been developed for the determination of flutamide and its degradation products. Using this method, the influence of important formulation factors on the stability of flutamide has been estimated. The stability studies have been carried out in solid state as well as in aqueous solution. The results obtained have shown a good stability for flutamide in solid state. This drug remained practically unchanged after a four-month assay in adverse temperature and humidity conditions. On the other hand, the results obtained from the stability study in solution during 12 days have shown that flutamide in aqueous solution underwent a clear degradation at mean or high temperature (22 degrees C, 37 degrees C) and acidic pH conditions (1.1). With respect to the influence of ionic strength, it has been found that the presence of sodium chloride prevents the degradation of flutamide in aqueous solution. The second-order kinetics model provides the best fit for highly degraded solutions.