More steps forward to optimize the dosing of hydroxychloroquine.

We read with great interest the article by Petri et al demonstrating that higher hydroxychloroquine (HCQ) blood levels were associated with lower risk of thrombotic event in patients with systemic lupus erythematosus (SLE). (1) A mean blood level of 1068 ng/mL and a most recent level of 1192 ng/mL and above had a protective effect. The dose response implied a therapeutic threshold of HCQ. However, a previous study indicated a range of HCQ blood level from 1177 to 3513 ng/mL predicted later development of HCQ retinopathy. (2) Obviously, there's a great overlap between the protective level from thrombosis and toxic level of retinopathy. The optimal therapeutic range is so narrow (1068 to 1177 ng/mL) that dose titration to target this level would be difficult in clinical practice. It seems that the dilemma of avoiding retinopathy while maintaining the benefit of HCQ still exists.