DoseCheckerComplete

Hydroxychloroquine retinopathy (HCR) is a potentially blinding disease. Once HCR is detected, there is no treatment and the disease often continues to progress, even when the medication is stopped. Hence, primary prevention by appropriate dosing of hydroxychloroquine offers the best chance of minimizing the risk of HCR.

Achieving this goal remains elusive. A key reason is disagreement in how to calculate dosages of hydroxychloroquine. (1,2) There are 2 methods: one uses ideal body weight (IBW); the other uses actual body weight (ABW). The IBW method assumes that hydroxychloroquine is stored mostly in lean tissue.(1) The daily dose must be normalized by lean body mass. This makes the calculation more complicated than the ABW method, which assumes that the drug is distributed evenly in muscle, skin, and fat.(3)


IBW Method:

The National Lung and Blood Institute formula is expressed in pounds: IBW (lb) = 4.28 × Height (in) − 134.32. It is then converted to kilograms.

Maximum Daily Dose = 6.5 (mg/kg/d) × IBW (kg).

The was the method recommended by the American Academy of Ophthalmology (AAO) from 2011 to 2014. The calculation uses the National Lung and Blood Institute IBW formula for women.(3) The app does not distinguish between men and women since 95% of HCR occurs in women; because the IBW calculation yields a lower value for women than for men of the same height, it results in a more conservative dosage for men. The IBW method may generate excessive dosing in very thin patients.

ABW Method:


Maximum Daily Dose = 5 (mg/kg/d) × ABW (kg)

This was the method recommended by the AAO in 2014. The ABW method may generate excessive dosing in obese patients.

Using both methods simultaneously:

Because of the inherent weaknesses in each method, a recent research letter in JAMA Ophthalmology (2018) recommended using both methods simultaneously.(4)

DoseCheckerComplete allows you to select either of the methods or to use both simultaneously. In addition, the app calculates an adjustable weekly dosing schedule.

Since the drug is only available as a 200-mg tablet, the app suggests a total weekly hydroxychloroquine dose using a combination of 400-mg and 200-mg daily doses. The total weekly dose is always the highest dose allowable, but always under the potentially toxic dose. When both methods are in use together, the app selects whichever method yields the lowest weekly dose.

DoseCheckerComplete is very easy to use:

The clinician enters the patient’s weight (and also the height if the Ideal Body Weight method is in use), then touches the calculate button. The recommended dosing appears immediately.

The dosing recommendations always fall within the approved drug labeling which eliminates the need for US Food and Drug Administration regulation as a class I mobile medical device.

To change the methods in use, touch the Settings Icon and make the changes. When you return to the main app page, the new settings will be active. To change from US Units to Metric, go to the same Settings page. The latest settings will be retained between uses of the app.

When the app is first downloaded, the default settings are US Units and use of both methods together.

References:

1. Browning DJ. The prevalence of hydroxychloroquine retinopathy and toxic dosing, and the role of the ophthalmologist in reducing both. Am J Ophthalmol. 2016;166(6):ix-xi.
2. Melles RB, Marmor MF.The risk of toxic retinopathy in patients onlong-term hydroxychloroquine therapy. JAMA Ophthalmol. 2014;132(12):1453-1460.
3. Browning DJ, Lee C, Rotberg D.The impact of different algorithms for ideal body weight on screening for hydroxychloroquine retinopathy in women. Clin Ophthalmol. 2014;8:1401-1407.
4. Perlman EM, Greenberg PB, Browning D, Friday, RP, Miller, JW. JAMA Ophthalmol. 2018;136:218-219.

Recent changes:
Maintenance updates