Pneumocystis Jirovecii Pneumonia in Non-HIV Patients

Pneumocystis jirovecii pneumonia (PCP) is a life-threatening opportunistic infection in immunocompromised patients. Non-HIV-related PCP has a rising incidence, faster progression, and higher mortality than HIV-associated cases. Trimethoprim-sulfamethoxazole (TMP/SMX) is first-line, but standard dosing (TMP 15-20 mg/kg/day) is associated with adverse reaction rates of 56%-72%, and prospective evidence is scarce. This prospective, multicentre, observational study aims to compare the efficacy and safety of low-dose (TMP \<15 mg/kg/day) versus conventional-dose TMP/SMX for non-HIV-related PCP, and to explore the value of therapeutic drug monitoring in individualising therapy, without interfering with routine clinical decisions. The investigators plan to enrol 480 patients aged ≥18 years with confirmed non-HIV-related PCP receiving TMP/SMX as initial treatment, excluding those with allergy, prophylaxis, treatment \<72 hours, or supratherapeutic dosing. The primary outcome is treatment failure at day 21 (all-cause death or new invasive ventilation). Secondary outcomes include day-8 oxygenation change, 30- and 90-day mortality, regimen completion, adverse events (CTCAE v6.0), and hospital/ICU stay. Propensity score matching will be the main analysis, with inverse probability weighting for sensitivity.