Mixtures of acidic and basic compounds

Sometimes a combination formulation requires the admixture of acidic and basic dmgs. One example (Septrin infusion) is discussed here. 

Because sulfamethoxazole (XVll) is a weakly acidic substance and trimethoprim (XVlll) is a weakly basic one, for optimal solubility basic and acidic solutions, respectively, are required. In consequence, in an ordinary aqueous 

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