To evaluate the prophylactic effect of sulfasalazine against Pneumocystis jirovecii pneumonia (PJP) among rheumatoid arthritis (RA) patients.
We used a nationwide Japanese multicenter RA database to extract data from 2005 and 2014. To identify PJP cases, we selected patients hospitalized for PJP and verified their diagnosis. Two control groups, one unmatched and the other matched for age, sex, glucocorticoid, methotrexate, and tacrolimus dosage, and the use (and type, if used) of biological disease-modifying antirheumatic drug were selected by incidence-density sampling. The odds ratios for PJP associated with sulfasalazine use and other clinical factors were estimated by exact and standard conditional logistic regression.
From 18,668 participants, 60 cases, 356 unmatched controls, and 337 matched controls were selected. None of the cases received sulfasalazine before PJP onset. A comparison of the cases with the unmatched controls showed that sulfasalazine use carried a decreased risk of PJP (adjusted odds ratio 0.18, 95% confidence interval 0.00-0.92). A comparison of the cases and matched controls also showed that sulfasalazine use had a decreased risk of PJP (0.08, 0.00-0.36). In an analysis of the cases and unmatched controls who did not receive sulfasalazine, an increased risk of PJP was associated with lung disease (3.88, 1.89-7.95) and the use of glucocorticoid (5.71, 2.68-12.19), methotrexate (5.25, 2.01-13.74), and tumor necrosis factor inhibitors (2.32, 1.10-4.93).
The results of this nested case-control study demonstrated the preventive effect of sulfasalazine against PJP. The results await confirmation by future prospective studies.