Dapsone safety in hematology patients: Pathways to optimizing Pneumocystis jirovecii pneumonia prophylaxis in hematology malignancy and transplant recipients.

Dapsone may be used for Pneumocystis jirovecii pneumonia (PJP) prophylaxis in hematology patients receiving immunosuppressive therapy or after hematopoietic stem cell transplant (HSCT) in the setting of trimethoprim-sulfamethoxazole (TMP-SMX) adverse drug reaction (ADR) history. Dapsone-induced hematological toxicities such as oxidative hemolysis may limit use in these patients and modern assessments of dapsone allergy cross-reactivity in non-HIV patients with a sulfonamide allergy are largely absent. The aim of this single-centre, retrospective study was to describe dapsone usage in hematology patients requiring PJP prophylaxis, including HSCT recipients, over a 12-month period in terms of indications, incidence of dapsone-attributed oxidative hemolysis, and immune cross-reactivity in those previously labeled with a sulfonamide allergy, as well as describing potential opportunities for first-line TMP-SMX PJP prophylaxis reintroduction. Of 24 patients meeting the study inclusion criteria, 12 (50%) were receiving dapsone PJP prophylaxis post-HSCT. No cases of breakthrough PJP infection were noted. Sixteen patients (67%) were initiated on dapsone to avoid the perceived risk of further myelosuppression with TMP-SMX and five patients (21%) because of prior delayed immune-mediated allergy to TMP-SMX. None experienced rash with dapsone therapy. Six patients (25%) were successfully rechallenged on TMP-SMX, including one patient with prior TMP-SMX-associated rash. Four (17%) patients had confirmed oxidative hemolysis, all resulting in dapsone cessation. Dapsone PJP prophylaxis in hematology patients was effective and safe, with nonlife threatening dapsone-related hemolysis noted in a small number. An absence of sulfonamide allergy cross-reactivity was noted, suggesting greater TMP-SMX rechallenges or desensitization could be considered in those receiving dapsone.