Short patients should have a dosage calculated by the traditional 6.5 mg/kg using ideal weight. Keep in mind that because of the slow action of the drug, intermediate doses can be achieved easily by variable intake (e.g., 300 mg/day is gained by alternating one and two pills on successive days).
Duration of Use
After five to seven years of HCQ use, the risk of retinal toxicity is above 1%, and the AAO recommends annual screening. This screening might begin earlier or occur more often in patients at unusual risk because of renal or liver disease (slower clearance), old age (harder to assess macular changes), underlying retinal disease, and other factors. Toxicity is rare under 1,000 gm of cumulative dosage (or about 16 gm/kg ideal weight). The higher these figures grow, the greater the risk. There are many patients with 25 years of HCQ use and no evidence for toxicity, but the longer the drug is used, the greater the likelihood of toxicity, making proper screening more critical.
Screening for Toxicity
Screening is necessary because the off-center (bull’s eye) pattern of early damage means that most patients keep good central vision initially and don’t notice the development of toxicity. Thus, counseling patients about the risk for toxicity and the need for screening is important when starting HCQ. Although patients should be aware of the need for good quality annual screens, much of the practical responsibility falls on the physician who sees the patient on a regular basis—to remind patients of the importance of screening or to refer appropriately. Many of the cases of toxicity that I see were missed initially because of irregular or poor screening. Screening cannot prevent toxicity, but it can catch it early enough to prevent a loss of visual acuity.
The new AAO recommendations make some important changes in the prior advice on how to screen. First, the subjective tests, such as the Amsler grid and automated visual fields, are recognized as variable in value because of variable performance—not only of the patient, but also of the doctor who may assume that a few “errors” are just noise in the test. Amsler grids (handheld grid patterns) are no longer acceptable because their results vary too often, and automated 10-2 visual field testing (i.e., field testing the central 10 degrees of vision) is accepted only with the proviso to be very alert with HCQ patients and retest if any new areas of sensitivity loss appear (see Figure 2). The new AAO recommendations also emphasize that ophthalmoscopic examination for “bull’s eye retinopathy” (see Figure 1) is not a screening test; fundus changes appear too late and represent retinal damage of such longstanding duration that the underlying retinal pigment epithelium cells have also degenerated.
