Trimethoprim sulfamethoxazole prophylaxis and serious infections in granulomatosis with polyangiitis treated with rituximab.

OBJECTIVE:To assess the association of trimethoprim sulfamethoxazole (TMP-SMX) prophylaxis with serious infections in rituximab-treated patients with granulomatosis with polyangiitis (GPA). METHODS:This retrospective cohort study included adults with GPA (2011-2020) within the United States Merative™ Marketscan® Research Databases with ≥6 months enrolment prior to first (index) rituximab treatment. We defined TMP-SMX prophylaxis as a ≥28-day prescription dispensed after or overlapping the index date. Serious infection was a hospital primary diagnosis for infection (excluding viral or mycobacterial codes). Secondary outcomes were outpatient infection, PJP, and adverse events potentially attributable to TMP-SMX. Cox proportional hazards regression assessed the association of time-varying TMP-SMX with outcomes of interest, adjusting for potential confounders. Individuals were followed until the outcome of interest, end of database enrolment, or Dec 31, 2020. RESULTS:Among 919 rituximab-treated individuals (53% female), mean age was 52.1 years (SD 16) and 281 (31%) were dispensed TMP-SMX within 30 days of index date. Over a median of 496 (IQR 138, 979) days, 130 serious infections occurred among 104 individuals (incidence 6.1 [95% CI 5.0-7.4] per 100 person-years). Time-varying TMP-SMX was negatively associated with serious infection (adjusted HR 0.5; 95% CI 0.3-0.9). The aHR for outpatient infections was 0.8 (95% CI 0.6-1.1). The estimate for PJP was imprecise (13 events, unadjusted HR 0.2; 95% CI 0.03-1.8). TMP-SMX was potentially associated with adverse events (aHR 1.3; 95% CI 0.9-1.9). CONCLUSIONS:TMP-SMX prophylaxis was associated with reduced serious infections in rituximab-treated GPA, but may increase adverse events, warranting further study of optimal prophylaxis strategies.