Aspirin for primary thrombosis prevention in the antiphospholipid syndrome: A randomized, double‐blind, placebo‐controlled trial in asymptomatic antiphospholipid antibody–positive individuals

Abstract

Objective To determine the efficacy of a daily dose of 81 mg aspirin in primary thrombosis prevention in asymptomatic, persistently antiphospholipid antibody (aPL)–positive individuals (those with positive aPL but no vascular and/or pregnancy events). Methods The Antiphospholipid Antibody Acetylsalicylic Acid (APLASA) study was a multicenter, randomized, double‐blind, placebo‐controlled clinical trial in which asymptomatic, persistently aPL‐positive individuals were randomized to receive a daily dose of 81 mg of aspirin or placebo. In a separate observational and parallel study, asymptomatic, persistently aPL‐positive individuals who were taking aspirin or declined randomization were followed up prospectively. Results In the APLASA study, 98 individuals were randomized to receive aspirin or placebo (mean ± SD followup period 2.30 ± 0.95 years), of whom 48 received aspirin and 50 received placebo. In the observational study, 74 nonrandomized individuals were followed up prospectively (mean ± SD followup period 2.46 ± 0.76 years); 61 received aspirin and 13 did not. In the APLASA study, the acute thrombosis incidence rates were 2.75 per 100 patient‐years for aspirin‐treated subjects and 0 per 100 patient‐years for the placebo‐treated subjects (hazard ratio 1.04, 95% confidence interval 0.69–1.56) (P = 0.83). Similarly, in the observational study, the acute thrombosis incidence rates were 2.70 per 100 patient‐years for aspirin‐treated subjects and 0 per 100 patient‐years for those not treated with aspirin. All but 1 patient with thrombosis in either study had concomitant thrombosis risk factors and/or systemic autoimmune disease at the time of thrombosis. Conclusion Our results suggest that asymptomatic, persistently aPL‐positive individuals do not benefit from low‐dose aspirin for primary thrombosis prophylaxis, have a low overall annual incidence rate of acute thrombosis, and develop vascular events when additional thrombosis risk factors are present.