Optometrists are on high alert whenever a patient marks down Plaquenil (hydroxychloroquine, Sanofi) on their list of medications. The rheumatoid arthritis mainstay, which is also used for systemic lupus erythematosus and autoimmune and dermatological conditions, can have dire visual consequences. Prolonged exposure can be toxic to the eye, resulting in retinopathy. Clinical signs of Plaquenil toxicity include maculopathy, retinal pigment epithelium changes, advanced retinopathy with bull's eye maculopathy characterized by a ring of parafoveal RPE depigmentation, central vision loss, decreased color vision, central scotomas, photopsia and visual field deficits.

But with 4.9 million prescriptions handed to patients in North America in 2016, it’s not going away. Now, to assist optometrists monitoring for Plaquenil toxicity, Canadian researchers developed an online calculator as a free Google spreadsheet accessible to anyone.

Clinical dosing of Plaquenil requires a negotiation between the patient’s rheumatologist and their eye care physician and is based, in part, on an individual patient’s weight, as well as risk factors for Plaquenil toxicity. It’s a careful balance that can require a deft hand and a little bit of forecasting.

Click image to use Plaquenil dosing calculator.

The calculator can help guide clinicians toward a suggested weekly dosing schedule. It takes into account the patient’s weight and risk factors for Plaquenil retinopathy. With the weekly regimens, in some cases, the daily dose may exceed the 5mg/kg/day limit, but the weekly dose does not exceed 35mg/kg/week, the creators explain.

The tool was devised using practice guidelines from the American Academy of Ophthalmology, the Royal College of Ophthalmologists, product monographs, relevant literature and other already available calculators for Plaquenil dosing. Additionally, they consulted with four academic rheumatologists and four pharmacists in the greater Toronto area to understand the general culture of prescribing Plaquenil.  

The team provided two layouts, one optimized for mobile device viewing and the other for desktop computers. 

Sivakumar G, Liu J, Sokoluk C, Ing E. Online calculator for hydroxychloroquine dosing. Can J Ophthalmol. February 18, 2020. [Epub ahead of print].