Failure of trimethoprim/sulfamethoxazole prophylaxis for Pneumocystis carinii pneumonia with concurrent leucovorin use.

Pneumocystis carinii is a common cause of pneumonia in patients with AIDS, however, the incidence has dropped with the availability of effective prophylactic regimens. First-line treatment for both acute Pneumocystis pneumonia and chronic prophylaxis is trimethoprim/sulfamethoxazole (TMP/SMX). This combination can cause hypersensitivity reactions as well as myelosuppression. The simultaneous administration of leucovorin during acute treatment has been shown to reduce the incidence of neutropenia, but may interfere with the efficacy of TMP/SMX. We report a case of P. carinii pneumonia in a patient with AIDS who failed TMP/SMX prophylaxis while taking leucovorin.