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Apr 27, 2020

What we need to know about hydroxychloroquine retinal toxicity during COVID-19

By: Doug Rett, OD, F.A.A.O n his blog, Doug Rett, OD, FAAO, digs deeper into questions every eye doctor has had at one point in his or her career. He sees patients and works with students and residents at the optometry clinic for the VA Boston Healthcare System and will use his blog to bring the teaching points he sees in clinic to a larger audience. Contact him at Disclosure: Rett has no relevant financial disclosures. About a year ago I wrote a piece on hydroxychloroquine retinal toxicity, in which I explored the drug’s mechanism and why it yields its characteristic bullseye. As we all know, hydroxychloroquine has been in the news lately as a possible treatment for COVID-19, so I thought it a good time to revisit what we know about hydroxychloroquine and how it affects the retina. I want to iterate here that this will not be an opinion on the usefulness of the medicine against COVID-19, but rather a primer for eye care providers to use when and if a patient presents with a recent history of hydroxychloroquine use. As I write this, there is a shortage of the medicine in some pharmacies, and it would stand to reason that if there is a spike in the number of patients using hydroxychloroquine, then there may be a spike in the number of patients with hydroxychloroquine retinal toxicity, especially if these patients are taking it at higher-than-recommended doses. Recall that the medication was first derived in the 1930s as chloroquine, a schizonticide (a killer of protozoa) used to treat malaria, which was itself derived from quinine, the primary treatment for malaria at the time. Soon after in the 1940s, a hydroxy-group was added to the chloroquine molecule to create hydroxychloroquine. This addition lessens (but does not eliminate) the ability of hydroxychloroquine to cross the blood-retinal barrier, thereby decreasing the retinal toxicity compared with chloroquine. Hydroxychloroquine acts against malaria mainly by elevating the pH level in lysosomes, making it difficult for protozoa to break down hemoglobin in red blood cells. As a friendly reminder, lysosomes are organelles within a cell that help digest material and break down waste. Lysosomes contain a lot of enzymes and typically operate in a fairly acidic (low pH) environment. So, when hydroxychloroquine raises the pH in parts of a malaria-infected cell, it inhibits polymerases necessary for the parasite’s protection and it causes an inability of the parasite to carry out hemoglobin digestion…… Read more: Source: Healio

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