To study the relation between blood concentration of hydroxychloroquine and the clinical efficacy of hydroxychloroquine sulfate in a series of patients with cutaneous lupus erythematosus (CLE).

Prospective multicenter study. A staff dermatologist blinded to blood hydroxychloroquine concentrations performed a standardized review of medical records and assessment of hydroxychloroquine efficacy in the following 3 categories: complete remission, partial remission (clearing of >50% of skin lesions), or treatment failure. Whole-blood samples were collected for measurement of blood hydroxychloroquine concentration.

Fourteen French university hospitals.

Three hundred consecutive patients with subacute or chronic CLE who had been treated with hydroxychloroquine for at least 3 months.

The statistical significance of correlation between blood hydroxychloroquine concentration and efficacy of hydroxychloroquine and the statistical associations in univariate and multivariate analyses of complete remission with several variables.

The study included 300 patients with discoid lupus erythematosus (n = 160), subacute CLE (n = 86), lupus erythematosus tumidus (n = 52), chilblain lupus (n = 26), and lupus panniculitis (n = 16); 38 of these patients had 2 or more associated forms. Median blood hydroxychloroquine concentration was significantly higher in patients with complete remission (910 [range, <50 to 3057] ng/mL) compared with partial remission (692 [<50 to 2843] ng/mL) and treatment failure (569 [<50 to 2242] ng/mL) (P = .007). In the multivariate analysis, complete remission was associated with higher blood hydroxychloroquine concentrations (P = .005) and the absence of discoid lesions (P = .004). Thirty patients (10.0%) had very low blood hydroxychloroquine concentrations (<200 ng/mL) and may be considered nonadherent to the treatment regimen.

Monitoring hydroxychloroquine blood concentrations might improve the management of refractory CLE.