Prophylactic Effect of Trimethoprim-sulfamethoxazole on Severe Infections in Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathy (IIM) is commonly treated with glucocorticoids and other immunosuppressants, which substantially increase the risk of opportunistic infections, including Pneumocystis jirovecii pneumonia (PJP). Therefore, trimethoprim-sulfamethoxazole (TMP/SMX) is frequently used as prophylaxis against PJP in patients with IIM. In addition to its role in PJP prevention, TMP/SMX has been reported to reduce the risk of severe infections in other immunosuppressed populations. We evaluated the association between TMP/SMX use and the risk of severe infections other than PJP in IIM. This retrospective, single-center study included 89 patients diagnosed with IIM who underwent remission induction therapy. After excluding 2 patients who developed PJP, the final study population consisted of 87 patients. We evaluated the incidence of severe infections during the follow-up period. Cox regression analysis was used to identify risk factors for severe infection. Sixteen patients developed severe infections other than PJP, with respiratory infections being the most common. Patients who received TMP/SMX had a significantly lower incidence of severe infections than those who did not. Respiratory tract infections were also significantly less common in patients using TMP/SMX. Multivariate analysis showed that older age increased the risk of severe infection (hazard ratio [HR] 1.063; 95% CI, 1.019-1.109; p=0.005), while TMP/SMX use significantly reduced the risk (HR 0.178; 95% CI, 0.056-0.57; p=0.004). TMP/SMX use was associated with a lower risk of severe infections in patients with IIM who underwent remission induction therapy, especially respiratory tract infections.