To the Editor:

We did not state in our article that the issue of the thromboprotective effects of antimalarials had only been addressed in studies involving populations without SLE but were instead referring to the findings of 2 prospective studies in non-SLE populations (1, 2). We referred to other descriptive and observational studies in SLE, and acknowledge that we did not refer to all available publications on this topic and that Wallace has previously questioned whether hydroxychloroquine prevented clot formation in SLE and showed a protective association between use of hydroxychloroquine and thrombosis in 92 patients with SLE (3). We would also like to mention a survival analysis by Ruiz-Irastorza et al, who showed that antimalarials were thromboprotective in SLE, with a hazard ratio of 0.28 (95% confidence interval 0.08–0.90) (4). A recent systematic review (5), also authored by Ruiz-Irastorza and colleagues, assimilates the body of evidence available up to the time of our article's publication. The information that our report adds to previous studies results from the use of an analytical method that addresses the issue of confounding by indication associated with the use of antimalarials in SLE. We designed our nested case–control study to adjust for the calendar year of the first visit to the clinic, the duration of followup, and the highest SLE disease activity measured over the 2-year period of observation. This allowed us to control for potential confounders such as disease activity, severity, and duration, and the results contribute to the overall growing evidence that support the notion that antimalarial treatments have a thromboprotective effect in SLE.

  • 1
    Carter AE, Eban R. Prevention of postoperative deep venous thrombosis in legs by orally administered hydroxychloroquine sulphate. Br Med J 1974; 923: 945.
  • 2
    Johnson R, Charnley J. Hydroxychloroquine in prophylaxis of pulmonary embolism following hip arthroplasty. Clin Orthop Relat Res 1979; 144: 1747.
  • 3
    Wallace DJ. Does hydroxychloroquine sulfate prevent clot formation in systemic lupus erythematosus? [letter]. Arthritis Rheum 1987; 30: 14356.
  • 4
    Ruiz-Irastorza G, Egurbide MV, Pijoan JI, Garmendia M, Villar I, Martinez-Berriotxoa A, et al. Effect of antimalarials on thrombosis and survival in patients with systemic lupus erythematosus. Lupus 2006; 15: 57783.
  • 5
    Ruiz-Irastorza G, Ramos-Casals M, Brito-Zeron P, Khamashta MA. Clinical efficacy and side effects of antimalarials in systemic lupus erythematosus: a systematic review. Ann Rheum Dis 2010; 69: 208.

Paul R. Fortin MD, MPH, FRCPC*, Hyejung Jung MSc†, Wendy Lou PhD‡, * University of Toronto, and Toronto Western Hospital, Toronto, Ontario, Canada, † McMaster University, Hamilton, Ontario, Canada and University of Toronto Toronto, Ontario, Canada, ‡ University of Toronto, Toronto, Ontario, Canada.