Objectives Past studies, mostly cross-sectional, have found a reduction in thrombosis in systemic lupus erythematosus (SLE) patients taking hydroxychloroquine. We examined the relationship between hydroxychloroquine and other medications with thrombosis in a large prospective SLE cohort.

Methods We studied 1795 SLE patients (56% Caucasian, 37% African American, 93.3% female, mean age 37.0±12.5) with no previous thrombosis prior to entry in the cohort. The primary outcome was first thrombotic event (arterial or venous). Univariate analysis and multivariable modelling were used to examine associations between prednisone, hydroxychloroquine, and NSAID use with the risk of thrombosis.

Results A total of 193 thrombotic events were observed over 10,508 person-years of follow-up (rate 18.4/1000 person-years). In the multivariable model controlling for age, traditional cardiovascular risk factors, and SLE disease activity, significant predictors for thrombosis included current prednisone dose (>20 mg/day, HR 4.2, p<0.0001) and Aspirin use (HR 1.9, p=0.0009). Hydroxychloroquine use remained protective for thrombosis (HR 0.7, p=0.012). Subgroup analysis revealed that the protective effect of hydroxychloroquine was stronger in antiphospholipid antibody positive patients (HR 0.6, p=0.0080) than among antiphospholipid antibody negative patients (HR 0.8, p=0.48).

Conclusions Current prednisone dose was found to be a significant independant predictor of thrombosis in SLE, after adjustment for disease activity. Current hydroxychloroquine use decreased the risk of thrombosis in this prospective cohort, particularly in those with positive antiphospholipid antibodies. Aspirin use was not protective, likely due to the bias of indication.

Disclosure of Interest None Declared