Protective effect of different doses of trimethoprim-sulfamethoxazole prophylaxis for early severe infections among patients with antineutrophil cytoplasmic autoantibody-associated vasculitis.

OBJECTIVES To analyse the protective effect of different doses of trimethoprim-sulfamethoxazole (TMP/SMX) prophylaxis for early severe infections in antineutrophil cytoplasmic autoantibody-associated vasculitis (AAV), considering time-varying changes. METHODS In this retrospective observational study, we assessed the protective effect of TMP/SMX within the first 6 months of diagnosis among Japanese patients with AAV. We included 250 consecutive patients with AAV who were admitted to our hospital. The protective effect of TMP/SMX against early severe infections was verified using Cox regression analysis along with potential confounding factors. Cox regression with inverse probability treatment weights for early severe infections was also performed as a sensitivity analysis. RESULTS Cox regression analysis showed that the reduced TMP/SMX exposure group had a significant protective effect against early severe infections (standard-dose group versus no TMP/SMX group: hazard ratio [HR] 0.393, 95% confidence interval [CI]: 0.139-1.11, p=0.077; reduced-dose group versus no TMP/SMX group: HR 0.418, 95%CI: 0.216-0.807, p=0.009), even when considering time-dependent changes. In the sensitivity analysis, the reduced-dose group still had a significantly lower risk of early severe infections than the no TMP/SMX group (HR = 0.393, 95%CI: 0.177-0.873, p=0.022). During follow-up, 18.0% of the patients discontinued TMP/SMX due to side effects. CONCLUSIONS TMP/SMX is highly effective in preventing severe infections among patients with AAV despite the high incidence of side effects. Further studies are needed to determine the optimal dose of TMP/SMX for preventing severe infections, especially considering renal impairment.