Background/Purpose: Hydroxychloroquine retinopathy (HCR) is a potentially blinding but largely preventable disease. The true prevalence of HCR is unknown among the 350,000 Americans who take the drug,¹ but it appears to be rising, related in part to changes in the definition of HCR. Despite improvements in diagnostic testing, it is still challenging to detect early signs of hydroxychloroquine toxicity.^2,3Moreover, once the disease is detected, there is no treatment and retinopathy often continues to progress even when the medication is stopped. Thus, primary prevention offers the best chance of managing HCR. Critical parameters that increase risk for HCR include the magnitude of dose and duration of therapy. Prescribing providers may not routinely calculate the optimal dose of hydroxychloroquine due to a number of factors, including: (1) toxicity is a cumulative effect and takes years to develop; (2) the calculations are cumbersome and time during a clinical encounter is short; (3) lack of familiarity with recommended dosing guidelines; and (4) controversy exists over how to calculate appropriate dosages.

Methods: Equations for calculating a low-risk hydroxychloroquine dose based on a patient’s actual body weight (ABW) and ideal body weight (IBW) were used to develop a novel iOS app to compare the two calculation methods and recommend a dosing strategy to maximize patient safety. The Smart BASIC iOS app was used for programming to devise a hydroxychloroquine dose calculating app compatible with the iOS operating system.

Results: We developed a free iOS App, DoseChecker, to provide a tool for rapid comparison of ABW and IBW hydroxychloroquine dose calculations for a patient at the point of care. Calculated data for an individual patient’s height and weight are reported for the two methods on a single screen output. The DoseChecker app recommends a maximum weekly hydroxychloroquine dose based on whichever dosing strategy (ABW vs. IBW) yields the lower weekly dose. The app then proposes an optimal weekly dosing strategy using a combination of 200mg and 400mg daily doses to reduce the risk of HCR by safely maximizing dosing of hydroxychloroquine.

Conclusion: By using DoseChecker to engage the patient in clinical decision making, the prescribing provider can educate patients regarding the risk factors for HCR and reinforce the critical need for ongoing ophthalmologic monitoring for HCR. We therefore anticipate that using the DoseChecker app in clinical practice will provide a convenient and practical bedside tool to facilitate the safe prescribing of hydroxychloroquine for primary prevention of HCR.

References:

1. Arch Ophthalmol 2014;132(12):1453-1460.
2. Clin Ophthalmol 2014:8:1389-1399.
3. Ophthalmology 2015 Feb;122(2):356-366.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dosechecker-solving-the-hydroxychloroquine-dosing-dilemma-with-a-smart-phone-app/