Antimalarial Adherence and Risk of Cardiovascular Events in Patients With Rheumatoid Arthritis and Systemic Lupus Erythematosus: A Population-Based Study

Objective. We aimed to assess the association between antimalarial adherence and cardiovascular events between incident rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) population-based cohorts.Methods. All patients with incident RA/SLE and incident antimalarial use in British Columbia, Canada, between January 1997 and March 2015 were identified using provincial administrative databases. The outcomes were incident cardiovascular events, including myocardial infarction (MI), stroke, or venous thromboembolism (VTE). The exposure was antimalarial adherence with levels: discontinuation (proportion of days covered [PDC = 0]), nonadherence (0 < PDC < 0.90), and adherence (PDC >= 0.90). We used marginal structural models to estimate the effect of antimalarial adherence on the rate of cardiovascular events, accounting for potential confounders.Results. We identified 16,538 individuals with incident RA/SLE and incident antimalarial use without any cardiovascular event before the index date. Over nine years mean follow-up, 2,174 incident cardiovascular events (13.2%) were observed. The adjusted hazard ratio (aHR) for incident cardiovascular events for antimalarial adherence relative to discontinuation was 0.72 (95% confidence interval [CI] 0.64-0.81) and 1.01 (95% CI 0.90-1.14) for nonadherence. Additionally, the aHRs for all cardiovascular events, MI, stroke, and VTE for adherence relative to nonadherence was 0.71 (95% CI 0.61-0.82), 0.62 (95% CI 0.51-0.75), 0.45 (95% CI 0.36-0.58), and 0.65 (95% CI 0.46-0.93), respectively. We found older age modified the association between antimalarial adherence and cardiovascular events (P = 0.02).Conclusion. When people newly diagnosed with RA or SLE take their antimalarial regularly as prescribed (PDC >= 0.90), they have a 29% lower risk of sustaining a cardiovascular event than patients with a lower degree of adherence (PDC < 0.90) and a 28% lower risk than if they discontinue antimalarials.