Aim: To investigate the safety and efficacy of dapsone dosing for PJP prophylaxis in immunosuppressed patients undergoing cancer treatment.
Method: A retrospective audit at a single tertiary site was conducted between 01/01/2022 - 31/12/2023. Patients prescribed dapsone for PJP prophylaxis with a diagnosis of cancer and receiving cancer treatment were included. Cancer treatments included chemotherapy, immunotherapy, targeted therapy, bispecific T-cell engager (BiTE) therapy, glucocorticoids or a combination. Data collected included type of treatment, glucose-6-phosphate dehydrogenase (G6PD) deficiency, occurrence of breakthrough PJP infections, incidence of adverse drug reactions (ADRs), and concurrent use of strong CYP3A4 inhibitors. Data was extracted using digital records and analysed accordingly.
Results: Ninety-one patients were identified. Of this, 7 patients received chemotherapy, 5 patients received immunotherapy, 2 patients received BiTE therapy, 7 patients received glucocorticoids, and 70 patients received combinations of cancer treatments. G6PD deficiency screening had a 95.6% completion rate (n = 87) with 1 patient screened demonstrating a deficiency. Twenty-two patients (24.2%) were prescribed 100mg once-daily, 68 patients (74.7%) were prescribed 100mg twice-weekly, and 1 patient (1.1%) was prescribed 100mg thrice-weekly. No patients were diagnosed with breakthrough PJP infections on any dosing regimen. There was a higher incidence of ADRs in the once-daily cohort at 50% (n = 11), with the twice-weekly cohort experiencing 14.7% (n = 10) [p-value = 0.029]. Haemolytic anaemia, oxidative haemoloysis and methemoglobinemia were the most common occurring of all cases. Concurrent use of strong CYP3A4 inhibitors were seen in 17 patients with 2 patients on twice-weekly dosing experiencing an ADR.
Conclusion: Twice-weekly dapsone dosing showed statistical significance for fewer ADRs compared to once-daily dosing for PJP prophylaxis. Twice-weekly dosing also demonstrated equal efficacy at PJP prophylaxis as once-daily dosing. Limited clinically significant interactions were identified despite the theoretical hypothesis of increased dapsone levels