Positivity for anti-RNP antibody is a risk factor for adverse effects caused by trimethoprim-sulfamethoxazole, a prophylactic agent for P. jiroveci pneumonia, in patients with connective tissue diseases.

OBJECTIVES: Trimethoprim-sulphamethoxazole (TMP-STX), an agent used for prophylaxis against pneumocystis pneumonia (PCP) in immunocompromised hosts, causes serious adverse effects (AEs) in some patients. The objective of this study was to identify the risk factors for AEs caused by TMP-STX in connective tissue disease (CTD) patients and to describe the clinical features of the AEs.

METHODS: The medical records of 539 patients (CTDs 312, pulmonary diseases 227) receiving TMP-STX for prophylaxis against PCP were reviewed retrospectively. Patients with human immunodeficiency virus were excluded. Univariate and multivariate analyses were conducted to identify the risk factors.

RESULTS: Adverse events caused by TMP-STX occurred in 22 of 312 (7.05 %) CTD patients, while only six of 227 (2.64 %) pulmonary disease patients developed AEs. The incidence of AEs was significantly higher in systemic lupus erythematosus (SLE) (11.0 %) and mixed connective tissue disease (MCTD) (33.3 %) patients than in other CTD patients. AEs occurred in 25 % of patients with anti-RNP antibody. Univariate analysis revealed that SLE, MCTD, and anti-RNP antibody were risk factors for AEs in CTD patients. Further multivariate analyses demonstrated that only anti-RNP antibody positivity was a risk factor for AEs. Systemic inflammation, including fever, was a characteristic manifestation of the AEs in CTD patients, particularly those with anti-RNP antibody.

CONCLUSIONS: Positivity for anti-RNP antibody is a risk factor for AEs caused by TMP-STX in CTD patients. Systemic inflammation, including fever, might be a characteristic feature of the AEs in CTD patients, particularly those with anti-RNP antibody.