Risk of Venous Thromboembolism Associated With Methotrexate Versus Hydroxychloroquine for Rheumatoid Arthritis: A Propensity Score-Matched Cohort Study

Abstract Aims : Patients with rheumatoid arthritis (RA) have an increased risk of venous thromboembolism (VTE), likely related to underlying inflammation. We examined VTE risk associated with two commonly used immunomodulators in RA patients, methotrexate and hydroxychloroquine. Methods and Results : Using U.S. Medicare claims data (2008-2017), we identified RA patients (≥65 years) who initiated methotrexate or hydroxychloroquine without prior use of any immunomodulators. The primary outcome was VTE, a composite of pulmonary embolism (PE) or deep vein thrombosis (DVT). Secondary outcomes included PE, DVT, and all-cause mortality. After 1:1 propensity score matching for confounding control, we identified 26,534 pairs of methotrexate and hydroxychloroquine initiators (mean (SD) age 74 (7) years; 79% female). During a total of 56,686 person-years of follow-up, 208 methotrexate and 83 hydroxychloroquine initiators developed VTE. The incidence rate of VTE was higher among methotrexate initiators (6.94/1,000 person-years) than hydroxychloroquine initiators (3.11/1,000 person-years) with a hazard ratio (HR) of 2.26 (95%CI 1.75, 2.91). Methotrexate initiators had a greater risk of PE (HR 3.30, 95%CI 2.28, 4.77) and DVT (HR 1.53, 95%CI 1.07, 2.19) than hydroxychloroquine initiators. All-cause mortality was similar between the two groups (HR 0.91, 95%CI 0.83, 1.00). Conclusion : In this large real-world cohort of older RA patients, treatment with methotrexate was associated with a 2-fold increased risk of VTE relative to hydroxychloroquine, although all-cause mortality was similar. Future experimental studies with non-user control groups are needed to determine the causal relationships between the study drugs and VTE and whether methotrexate elevates or hydroxychloroquine reduces the risk of VTE.