Ideal Body Weight for Calculating Hydroxychloroquine Dosage
The most important risk factor for hydroxychloroquine retinopathy is the daily dose of the drug. If a patient is overweight, one should use the ideal body weight to assess whether the doaily dose is in the toxic range (>/= 6.5 mg/kg/day). This graph shows various formulas that have been proposed for deriving ideal body weight for women, because virtually all cases of hydroxychloroquine toxicity have been female. The usual hydroxychloroquine dose that is prescribed is 400 mg/day. For this dosage, any woman with an ideal body weight less than 135 pounds would be in the toxic dose range. As one can see, the height that corresponds to an ideal body weight of 135 pounds varies across the formulas. The author uses the National Heart Lung and Blood Institute Table (NHLBI table, the blue crosses), which translates into a threshold of 5 feet 3 inches. Therefore, if a woman is 5 feet 3 inches or shorter, she should not be taking 2 tablets of Plaquenil (hydroxychloroquine) per day. A safe dose would be 2 tablets one day alternating with 1 tablet the next day, which gives an average daily dose of 300 mg - in the safe range.