Trimethoprim-sulfamethoxazole in the treatment of adults with pneumonia due to Pneumocystis carinii.

The use of trimethoprim-sulfamethoxazole (TMP-SMZ) for the treatment of pneumonia due to Pneumocystis carinii has not been as rigorously assessed in studies of adults as in pediatric studies that have included patients randomly assigned to receive either pentamidine or TMP-SMZ. Nonetheless, it was shown that 80% of adults with histologically proved pneumocystis pneumonia who were treated with TMP-SMZ intravenously for at least four days or orally for at least nine days (total daily dose, 10-20 mg/kg) responded clinically and radiologically. Recipients of organ transplants and patients with lymphomas or lymphatic leukemia predominated in these studies. The median time to improvement was four days. TMP-SMZ therapy was continued for up to six days before a change to pentamidine was considered. Clinical failures of treatment were associated with delayed diagnosis and initiation of treatment, poor absorption of the orally administered drug, and concomitant life-threatening infections. Thus, a regimen involving initial intravenous therapy with doses of 15-20 mg/kg per day, with subsequent reduction of dosage or change to oral medication if improvement is rapid, was developed. With large initial intravenous doses, the monitoring of drug levels in the serum may not be necessary. Historical comparisons show that treatment of pneumocystis pneumonia with TMP-SMZ is associated with a better response rate and fewer side effects than is treatment with pentamidine.