Safety of the concomitant use of methotrexate and a prophylactic dose of trimethoprim-sulfamethoxazole.

The objective of this study was to investigate risk factors for cytopenia when a prophylactic dose of trimethoprim-sulfamethoxazole (TMP-SMX) was co-administered with methotrexate (MTX). Patients who received MTX with or without a prophylactic dose of TMP-SMX were included. Patients who received a therapeutic dose of TMP-SMX were excluded. The MTX-alone and MTX with TMP-SMX groups (MTX group and MTX + TMP-SMX group, respectively) were matched in a 4:1 ratio according to age, creatinine level, mean corpuscular volume and MTX dose. Cytopenia was defined as a haemoglobin level decrease by > 2 g/dl, platelet count of < 150,000/mm or white blood cell count of < 3500/mm. The Cox proportional hazards model was used to evaluate risk factors for cytopenia in patients administered with MTX. The incidence of cytopenia did not significantly differ between the MTX group and MTX + TMP-SMX group (5.0 vs 5.7%, p > 0.999). According to the Cox proportional hazards model, chronic liver disease (hazard ratio [HR] 5.829, 95% confidence interval [CI] 1.211-28.063, p = 0.028) was associated with an increased risk of cytopenia. However, the concomitant use of a prophylactic dose of TMP-SMX (HR 1.717, 95% CI 0.352-8.371, p = 0.504) was not significantly associated with an increased risk of cytopenia. Compared with the use of MTX alone, the concomitant use of MTX with a prophylactic dose of TMP-SMX was not significantly associated with an increased risk of cytopenia. Thus, a prophylactic dose of TMP-SMX can be safely used with MTX.