Efficacy and safety of a low-dose sulfamethoxazole/trimethoprim regimen in preventing pneumocystis pneumonia: A retrospective study using a large-scale electronic medical record database.

Introduction: Sulfamethoxazole/trimethoprim (ST) is a first-line drug for preventing pneumocystis pneumonia (PCP). Several small-scale studies have suggested the usefulness of the low-dose regimen of ST (200/40 mg/day) over the standard-dose one (400/80 mg/day). Thus, this study aimed to investigate the efficacy and safety of low-dose and standard-dose regimens of ST in preventing PCP in patients with non human immunodeficiency virus infection using a large-scale electronic medical record database.

Methods: This retrospective study included patients who received ST prophylaxis for PCP registered in the RWD database between June 2007 and February 2023. Patients received either standard-dose (400/80 mg/day) or low-dose (200/40 mg/day) regimen groups. The incidence of cases initiated PCP therapeutic dose (ci-PCPTD) (ST ≥ 3600/720 mg/day) and adverse events (AEs) was evaluated, and risk factors for ci-PCPTD were investigated.

Results: A total of 11,384 patients received the standard-dose, whereas 7973 received the low-dose regimen groups. No significant difference in the cumulative incidence of ci-PCPTD was observed between the standard-dose (0.67%) and low-dose regimen group (0.47%). Lung disease was a significant risk factor for ci-PCPTD. The cumulative incidence of ci-PCPTD in patients with acute exacerbation of interstitial pneumonia was 1.3% in both groups, and no significant difference was observed between the two groups. The low-dose regimen group had a lower incidence of all AEs than the standard-dose regimen group.

Conclusion: These results based on a large-scale electronic medical record database provide important evidence supporting the clinical significance of low-dose regimen of ST.