Am I taking the right amount of hydroxychloroquine (Plaquenil)?

Hydroxychloroquine (Plaquenil): Am I taking too much?

Hydroxychloroquine is an oral medication used in a variety of autoimmune conditions. Side effects have been discussed previously but today we will focus on eye side effects. A number of side effects are possible ranging from vision changes to double vision to asymptomatic changes in various parts of the eye.

The Risk of Retinopathy with Hydroxychloroquine

"Retinopathy" is one of the more worrisome side effects of Hydroxychloroquine. At appropriate doses, studies show that the risk appears to be about 1 % of patients at 5 years of use and 2 % at 10 years. After 20 years, the risk may rise to 20 %. Once the retinal toxicity from hydroxychloroquine occurs, it is believed that the changes in the retina are permanent. Furthermore, the disease can even progress even if hydroxychloroquine is stopped.  

 

Risk Factor for Retinal Toxicity

Retinal damage can occur in anyone. However, the risk may be increased if the following risk factors are present

• Longer Duration of use (cumulative dose)
• Renal or hepatic functional impairment. Compromised kidney and/or liver function can lead to increased accumulation of hydroxychloroquine in the tissues.
• Age over 60 years.
• Preexisting retinal disease
• Concurrent tamoxifen therapy

What dose should I take?

It's clear that taking the appropriate dose reduces (but does not eliminate) the chance of side effects. The optimal dose is 6.5 mg for every kg of lean body weight (not simply what the patient weighs). "Lean body weight" is essentially the patients expected weight for their height and gender - it does not include the "extra" weight that some might carry. Instead of calculating lean body weight, some clinicians advocate simply using the patient's true body weight and multiplying by 5 (instead of 6.5).  In our clinic we typically dose hydroxychloroquine according to the following grid:

Hydroxychloroquine Dosing

Conclusion

The risk of eye related toxicity is low in the first 5-10 years of hydroxychloroquine use provided the dosing is respected. This study has had great importance as it has further helped to define risk and has encouraged changes in screening guidelines. These guidelines now include an initial examination but dedicated yearly screening to begin only after 5 years in otherwise healthy individuals deemed at low risk for eye problems.

Reference

(1) Melles & Marmor. The Risk of Toxic Retinopathy in Patients on Long-term Hydroxychloroquine Therapy. JAMA Ophthalmolol. 2014;132(12):1453–1460.