For a study, it was determined that in rheumatoid arthritis (RA) patients, immunosuppressive drugs (ISPs) increased the risk of Pneumocystis jirovecii pneumonia (PCP). Trimethoprim/sulfamethoxazole (TMP/SMX) was an effective preventive antibiotic for PCP, but it had substantial side effects and should only be used in high-risk individuals. Researchers wanted to determine the risk factors for PCP in RA patients as well as the criteria for TMP/SMX administration. This retrospective cohort research looked at data from 2640 individuals diagnosed with RA between 2010 and 2014 who had not taken TMP/SMX as a preventative treatment. The clinical parameters of patients with PCP (PCP group, n=19) and those without PCP (non-PCP group, n=2621) were compared to determine the risk factors for PCP. The PCP group was older (70 vs. 64 years old), had higher prednisolone (6.2 vs. 2.4 mg/d) and methotrexate (7.7 vs. 5.2 mg/wk) dosages, and had more ISPs (1.3 vs. 0.8) (P<0.05). They used a scoring system based on odds ratios (ORs) derived for these characteristics (methotrexate 6 mg/wk OR=4.5, 1 point; age 65 years, OR=3.7, 1 point; 2 ISPs, OR=3.7, 1 point; prednisolone 5 mg/d, OR=12.4, 3 points) to stratify PCP risk. PCP was found in 0.04% of patients with a score of 0 to 2 points, 2.3% of those with a score of 3 to 4 points, and 5.8% of those with a score of 5 or more points.

TMP/SMX for PCP prophylaxis was advised for RA patients who scored at least 5 points on our PCP questionnaire.