Hydroxychloroquine blood levels may predict future retinopathy in patients with systemic lupus erythematosus (SLE), according to study results published in Arthritis & Rheumatology.

One of the major long-term side effects of hydroxychloroquine treatment is retinopathy. In 2016, the American Academy of Ophthalmology revised the recommended dose of hydroxychloroquine from 6.5 mg/kg to <5 mg/kg, without evidence that a lower dose would have the same efficacy for SLE and protect against thrombosis and cardiovascular risk factors.

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The objective of this study was to evaluate the role of hydroxychloroquine blood levels testing in identifying future retinopathy in SLE.

Researchers evaluated the data of 537 patients with SLE from the Hopkins Lupus Cohort who were followed-up quarterly or more frequently if clinically necessary. Patients who were prescribed hydroxychloroquine had their blood levels measured at each visit starting in 2013, and they were also examined by retina specialists at the Johns Hopkins Wilmer Eye Institute in Baltimore, Maryland.

Results revealed that the overall prevalence of hydroxychloroquine toxicity in patients with SLE was 4.3% (n=23), with higher prevalence in men than in women (9.3% vs 3.8%, P =.1029). Hydroxychloroquine toxicity was higher in whites (5.6%) compared with other ethnic groups, and also more prevalent among patients aged 45 to 59 years (4.4%) and ≥60 years (10.1%) compared with patients aged ≤45 years (0.5%). 

Higher risk for toxicity was indicated in patients who used hydroxychloroquine for at least 16 years (P =.0024 and P =.0006 for trend test), and patients with a higher body mass index (P =.0160 for trend test). Both the mean (P =.0124) and maximum (P =.0340) hydroxychloroquine blood levels were found to predict future retinopathy. In patients with SLE treated with hydroxychloroquine, the risk for retinopathy was 1% in the first 5 years, 1.8% from 6 to 10 years, 3.3% during 11 to 15 years, 11.5% during 16 to 20 years, and 8.0% after 21 years of therapy.

Study researchers concluded that hydroxychloroquine blood level testing may effectively predict the risk for retinopathy, and give clinicians an insight as to whether to decrease hydroxychloroquine dose or increase monitoring in patients with high hydroxychloroquine blood levels.

Reference

Petri M, Elkhalifa M, Li J, Magder LS, Goldman DW. Hydroxychloroquine blood levels predict hydroxychloroquine retinopathy [published online September 18, 2019]. Arthritis Rheumatol. doi:10.1002/art.41121