Background Antimalarials (AMs) have shown to exert a thromboprotective effect in SLE patients, but studies thus far have been limited to North American and European patients. This study was conducted to assess whether a similar effect is observed in Latin American SLE patients.

Materials and methods SLE patients with a recent diagnosis (≤2 years) recruited and followed longitudinally as part of the GLADEL cohort were examined to establish risk factors for thrombotic events (TEs) and the possible preventive role of AMs. The end-point of this study was thrombosis defined as either arterial or venous occurring after entry into the cohort.

Independent variables included were socio-demographic characteristics, clinical manifestations as measured by the ACR classification criteria, laboratory, history of previous TEs and hospitalisation. For descriptive purposes, patients were divided according to use or non-use of an AMs agent (chloroquine and/or hydroxychloroquine) based on each patient’s entire follow-up period during the study. Patients were classified as “users” if they had received AMs for at least 6 months, whereas “non-users” comprised patients who had received AMs for less than 6 months or who had never received them.

Treatment with AMs, glucocorticoids and anticoagulants along with hospitalizations were considered as time-dependent covariates. The effect of AM use on thrombosis after adjustment for potential confounders (variables known to affect thrombosis and the use of AMs) was examined using a multivariable Cox regression model. A backward selection algorithm was used to select the variables retained in the model with α-level to stay in the model set to 0.05.

Results Of the 1,480 patients included in the GLADEL cohort, 1,208 (82%) were considered AMs users with median exposure time of 42.1 months (Q1–Q3: 19.1–62.3). TEs occurred in 103 (7%) of the patients during a median follow up time since enrolment of 15.4 months (Q1–Q3: 4.6–38.2). The rate of thrombosis for AM users was 1.44 per 100 patient/years of follow-up vs. 3.01 for non-AM users (HR 0.55, 95% CI: 0.37–0.82).

After adjusting for potential confounders in the Cox proportional hazards regression model, the use of AMs was associated with a 43% reduction in the thrombosis rate (HR 0.57, 95% CI: 0.38–0.85). Other variables significantly associated with TEs are depicted in Table 1.

Conclusions After adjusting for possible confounding factors related to AMs use, a clear protective effect of AMs in the development of TEs in SLE patients from this Latin American cohort was observed.

Acknowledgements On behalf of the Grupo Latino Americano De Estudio del Lupus (GLADEL) cohort.