Plasma hydroxychloroquine concentrations and efficacy in rheumatoid arthritis

Plasma levels of hydroxychloroquine (HCQ) and its metabolites were measured, by high performance liquid chromatography, in 37 rheumatoid arthritis patients who could be clearly distinguished as responders (n = 28) or nonresponders (n = 9) to HCQ, 400 mg/day. Efficacy in both groups was determined by the patients' erythrocyte sedimentation rates, joint counts, morning stiffness, global assessments, concurrent drug therapies, and grip strength. The response rate was 76%. Responders had a mean HCQ level of 213 ng/ml, versus 306 in nonresponders (P less than 0.05). The mean level of HCQ plus total metabolites in responders was 363 ng/ml, versus 554 in nonresponders (P less than 0.01). We conclude that monitoring plasma HCQ levels is unlikely to be helpful in individualizing effective drug dosage.