Simultaneous solubility and dissolution rate of sulfamethoxazole and trimethoprim in binary mixture

The solubilities of trimethoprim in solutions with different pH values decreased in the presence of sulfamethoxazole, while that of the latter increased in the presence of the first. The dissolution rate of trimethoprim in HCl (0.1 mol/1) was the same in the presence and absence of sulfamethoxazole. That of sulfamethoxazole however, decreased in the presence of trimethoprim. The different reasons were explained.