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J. S. Lyons, M. L. Severns, V. L. Patton, A. Chetwynd; Measuring Hydroxychloroquine Dosage to Predict Retinal Dysfunction. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5019.
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To evaluate various ways of measuring Hydroxychloroquine (HCQ) dosage to see which best correlate with retinal dysfunction. We used several measures comparing daily dosage (mg) ,daily dosage relative to body weight ( mg./kg.), total cumulative dosage (gm.), and total cumulative dosage relative to body weight (gm./kg.).
We collected and analyzed data from 131 eyes of 62 patients taking Plaquenil who were referred for testing. Retinal dysfunction was assessed using multifocal ERG ring ratios, as described in reference 1. We classified an eye as abnormal if any ring from 1 to 4 had a ring ratio greater than the 99th percentile of the normal population.
Retinal dysfunction, as measured by the multifocal ERG, is not highly related to the daily dosage of drug in mg. Eight eyes of 4 patients who were taking 200 mg/day exhibited dysfunction, or 24% of all patients with retinal damage. Retinal dysfunction, as measured by the multifocal ERG, is not highly related to the daily dosage of drug in mg/kg/day. The lowest dosage at which a patient exhibited retinal dysfunction was 1.8 mg/kg/day. Retinal dysfunction, as measured by the multifocal ERG, is related to the cumulative dose of the drug in grams. For example, 44% of the eyes of patients with 1500-1999 grams cumulative dosage were abnormal. A better predictor of retinal dysfunction is the cumulative dose of Plaquenil per kilogram of body weight (CDBW).There is a striking increase in the fraction of patients with retinal dysfunction above ~15 g / kg
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