The solubility of trimethoprim (TMP) and sulphamethoxazole (SMX) in binary solvents were studied to describe the solute-solvent interactions. Binary mixtures consisting of n-hexane-ethyl acetate, ethyl acetate-methanol and methanol-water systems were employed in this study. When solubilities were obtained for individual components, TMP exhibited solvation in ethyl acetate- methanol mixtures, while SMX showed weaker solute-solvent interactions in the above solvent series. At peak solubility, the solubility of SMX was around 8 times higher than that of TMP when these drugs were combined, SMX lowered the solubility of TMP to the tune of 13 to 74%. Similarly TMP suppressed the solubility of SMX to an extent of 10 to 94%. In water, though the mutual solubility was reduced, the solubility ratio of TMP to SMX was found to be 1:4 on the mole fraction scale. It is interesting because the dose ratio prescribed for TMP to SMX was 1:5. Evaluation of solubility parameters is difficult, because of the suppression of solubility by the other component.
|Number of pages||5|
|Publication status||Published - 1996|