A Comparison of the in vitro Activities of Sulfamethoxazole and Sulfadiazine Combinations with Trimethoprim

The sensitivity of 125 strains of 13 species or genera of bacteria to sulfamethoxazole (SMZ), sulfadiazine (SDZ), trimethoprim (TMP), SMZ + TMP and SDZ + TMP was determined by means of trays. A comparison of all combinations of the different concentrations used shows that SMZ + TMP is in 1 case and SDZ + TMP in 4 cases more effective against the 13 species or genera tested than the other combinations. SMZ and SDZ were equally effective in synergistic action (as shown by the FIC indices) against the various kinds of bacteria.