High rates of Pneumocystis carinii pneumonia in allogeneic blood and marrow transplant recipients receiving dapsone prophylaxis.

Chemoprophylaxis for Pneumocystis carinii pneumonia (PCP) is routinely given after allogeneic blood or marrow transplantation. We evaluated the effectiveness of dapsone prophylaxis (50 mg orally twice daily, 3 times per week) compared with twice-weekly trimethoprim-sulfamethoxazole (TMP-SMZ) in preventing PCP after allogeneic blood or marrow transplantation. Patients included all (n=646) who received allogeneic blood or marrow transplants between 1 September 1993 and 31 December 1996 who survived at least 100 days after transplantation. A cohort of 111 dapsone recipients was compared with the remaining 535 who received TMP-SMZ. Ten patients developed PCP; 8 were taking dapsone. PCP incidence in the TMP-SMZ cohort was 0.37% versus 7.2% for dapsone. The relative risk for PCP associated with dapsone use was 18.8 (P<.001) and was not accounted for by age, clinical extensive chronic graft-versus-host disease, donor source, or malignant relapse. Dapsone prophylaxis at this dosage is associated with significantly higher rates of PCP than is TMP-SMZ after allogeneic marrow transplantation. We advise caution in prescribing alternatives to TMP-SMZ prophylaxis in this setting.