Background Hydroxychloroquine is one of the major treatment of SLE, but its effectiveness is impaired by non-adherence, reported to range from 3% to 85% in SLE patients. Our objective was to assess the associations of severe non-adherence to HCQ, objectively assessed by HCQ serum levels, and risks of SLE flares, damage, and mortality over 5 years of follow-up.
Methods The SLICC Inception Cohort is a multicenter initiative (33 centers; 11 countries). Serum of patients taking HCQ for at least 3 months, sampled at enrolment or during the first-year follow-up visit, were analyzed. Severe non-adherence was defined by a serum HCQ level <106 ng/ml or <53 ng/ml, for daily HCQ doses of 400 or 200 mg/d, respectively. Association with the risk of a flare (defined as a SLEDAI-2K increase ≥4 points, initiation of prednisone or immunosuppressive drugs, or new renal involvement) was studied with logistic regression, and association with damage (first SLICC/ACR Damage Index (SDI) increase ≥1 point) and mortality were studied with separate Cox proportional hazard models.
Results Of 1849 cohort subjects, 660 patients (88% women) were included. Median [interquartile range] serum HCQ was 388 ng/ml (244–566); 48 patients (7.3%) had severe HCQ non-adherence. No factors were clearly associated with severe non-adherence. Severe non-adherence was independently associated with flare (OR 3.38; 95% CI 1.80–6.42) and of an increase in the SDI within each of the first 3 years (HR 1.92 at 3 years; 95% CI 1.05–3.50). Eleven patients died within 5 years, including 3 with severe non-adherence (HR 5.41; 95% CI 1.43–20.39).
Conclusions Severe non-adherence was independently associated with the risk of an SLE flare in the following year, with early damage and 5-year mortality. Our results suggest the benefits of testing of detecting severe non-adherence and dedicating more resources and more time to these patients, to improve their long-term prognosis.
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