Trimethoprim-sulfamethoxazole in the treatment of bacterial endocarditis.

The combination of sulfamethoxazole (SMZ) and trimethoprim (TMP) in a 5: 1 ratio has not previously been evaluated as the sole antimicrobial agent in treatment of bacterial endocarditis. Bacteremia was suppressed in three patients with Streptococcus viridans endocarditis; however, one patient relapsed three days after cessation of therapy. Two patients treated for six and eight weeks for Pseudomonas cepacia endocarditis relapsed within two weeks of stopping chemotherapy. In one patient with endocarditis due to a susceptible Staphylococcus aureus,. treatment was stopped after two days because of lack of clinical improvement and of increasing numbers of organisms on quantitative blood cultures. Review of the literature suggests that administration of polymyxin or another appropriate antimicrobial agent may increase the effectiveness of TMP-SMZ in the treatment of bacterial endocarditis. Since effective antibacterial therapy is available for many organisms causing endocarditis, future evaluation of TMP-SMZ in endocarditis should be limited to those situations in which either no other effective therapy is known or host factors such as allergy to penicillin exist.