Failure of trimethoprim-sulfamethoxazole in the therapy of recurrent Pneumocystis carinii pneumonia.

The use of trimethoprim-sulfamethoxazole in the treatment and prophylaxis of Pneumocystis cariniii is well established. Treatment failure with this regimen has been ascribed to inadequate antibiotic serum concentrations. We describe an immunosuppressed patient with recurrent Pneumocystis carinii pneumonia who failed to respond to trimethoprim-sulfamethoxazole therapy despite high antibiotic serum concentrations. Subsequently, a response to pentamidine isethionate was obtained. The reason for failure and therapeutic implications in patients with Pneumocystis carini pneumonia who have received trimethoprim-sulfamethoxazole are discussed.