The Effect of Trimethoprim on the Activity of Sulfonamides and Antibiotics in Experimental Infections

The evidence for in vivo potentiation of sulfonamides and antibiotics by trimethoprim (2,4-diamino-5-[3,4,5-trimethoxybenzyl]pyrimidine) is reviewed. The proportion of one part trimethoprim to five parts sulfamethoxazole provides substantially increased protection over that of either substance alone against a broad spectrum of pathogenic bacteria. The simultaneous administration of folinic acid or thymidine does not interfere with the potentiative properties of trimethoprim. In some instances, trimethoprim potentiates the in vivo antibacterial activity of antibiotics, but this effect is not consistent either for a particular antibiotic or for a specific organism.