Background Concurrent use of methotrexate (MTX) and trimethoprim-sulfamethoxazole (TMP-SMX) has been linked to the development of cytopenia as a result of reduced renal clearance of MTX. However, the risk of adverse outcomes has not been estimated in a population setting.
Objectives This study aimed to examine the risk for emergency department visits or hospitalisation after concurrent use of MEX and TMP-SMX in patients with rheumatoid arthritis (RA) in Taiwan using the National Health Insurance (NHI) data.
Methods This was a retrospective cohort analysis of RA patients identified from the entire NHI database which contains essentially all residents in Taiwan. The case definition of RA was based on a rheumatologist diagnosis with a verification of expert panel commissioned by the Administration of National Health Insurance. Overall we identified 30,285 RA patients between 2000 and 2010. RA patients filled prescription for MTX in 453,114 person-quarters in which 9018 person-quarters they also filled a prescription for TMP-SMX. The main outcome measure was emergency department visit or hospital admission in person-quarters with concurrent fills of MTX and TMP-SMX compared with the rates in person-quarters with MTX prescription only. Multivariable logistic regression was used to adjust for age, sex, comorbidity, and socioeconomic status with a Generalised Estimating Equation (GEE) model to calculated the crude ORs (95% CIs) and adjusted ORs.
Results Hospitalisations were more common in person-quarters with MTX and TMP-SMX use (688 events/8330 quarters) compared with quarters with MTX use alone (20,616 events/423,480 quarters) with a crude OR of 1.49 (95% confidence interval [CI], 1.36–1.62] and an adjusted OR of 1.45 (95% CI, 1.33–1.58). However, the risk for emergency department visits associated with MTX and TMP-SMX use (536 events/8,482 person-quarters) was not higher (21,115 events/422,981 person-quarters). The crude OR was 1.08 (95% CI, 0.97–1.19) for emergency department visits and the adjusted OR was 1.05 (95% CI 0.95–1.15]).
Conclusions MTX use along with TMP-SMX is associated with an increased risk for hospitalisations which suggests a significant drug interaction between MTX and TMP-SMX in RA patients.
Disclosure of Interest None declared
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