| Identifier |
Ethambutol_Optic_Neuropathy |
| Title |
Ethambutol Optic Neuropathy |
| Creator |
Andrew G. Lee, MD; Spencer Barrett |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (SB) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Subject |
Ethambutol; Neuropathy; Vision Loss |
| Description |
Dr. Lee lectures medical students on ethambutol optic neuropathy. |
| Transcript |
So today we're gonna be talking about ethambutol. As you know ethambutol is a medicine that is used for the treatment of Mycobacterium. Worldwide, the most common indication is for Mycobacterium tuberculosis, but in the United States we have a lot of a different type of Mycobacterium, which is Mycobacterium Avium Complex (M.A.C) or Mycobacterium Avium Intracellulare, and a whole host of other different species. So both the treatment of TB and M.A.C. use ethambutol. It's super important that you know about ethambutol because it causes vision loss as a side effect. It's usually painless progressive loss of vision. It's central, and so it produces a central scotoma or a cecocentral scotoma. They have decreased acuity, and usually there's no finding on the exam. So the nerve looks normal initially. It's a retrobulbar optic neuropathy, and then it becomes pale over time. So we never want to have the person end up with optic atrophy. We want to diagnose the patient before we get to the optic atrophy. Once the nerve turns pale the chance of recovering the vision is low. Ethambutol toxicity is a dose-dependent phenomenon. Once you get above 15 milligrams per kilogram you're gonna be entering into a toxic range, but there is essentially no safe dose of this drug. And as opposed to hydroxychloroquine and chloroquine, which are cumulative dose dependent, you can lose your vision from ethambutol in the first two weeks or first two months. And so we have to follow the patient very closely in the beginning, especially once you start getting into numbers like 25 milligrams per kilogram or greater. And sometimes a loading dose for M.A.C. is very high, and they might be in the numbers like 25 to 30 milligrams per kilogram. So those patients are particularly high risk; especially if they have renal disease. So we should dose-adjust the ethambutol if we have renal disease, and patients with M.A.C and tuberculosis tend to lose weight over the course their treatment. Many of our M.A.C patients are actually transplant patients, so those patients are going to be frail and losing weight and their "mg/kg" might be going up because their "kilograms" is going down, not because we're actually giving them more medicine. So we should tell the patient that if they have vision loss and they're on ethambutol that they should stop the medicine, and we should examine them. Obviously, we're not the prescribing physicians, so we should call the primary and the prescribing doctor before making any adjustment of the medicines. And because there's no pre-screening abnormality, it's not like hydroxychloroquine where we can do MERG, spectral domain OCT, or Humphrey's. Really the only thing we can do is say ‘Yes or no, you're having decreased vision'. So somebody has to check their vision every month. It doesn't have to be you. It doesn't have to be an ophthalmologist. It doesn't even have to be an eye care provider. It just has to be somebody. So I give them a copy of a Snellen chart on a piece of paper, and we give them an Amsler grid to check themselves. So if there's any decreased acuity, you're going to bring them in. We're going to do a field; we're gonna be looking for the central scotoma. We're gonna do an OCT. We're gonna look for optic atrophy. But hopefully we won't see any of that. If we stop the medicine early enough, it's reversible. If you don't stop the medicine early enough, it'll just keep progressing. And the progression can occur for months after discontinuation of the medication, which is a little bit counterintuitive given the half-life of ethambutol. In patients who have TB and have INH on board: if they continue to lose the vision after stopping the ethambutol, we might also stop the isoniazid (INH). And in M.A.C., the other M.A.C. drugs don't usually cost vision loss so pretty much it's limited to ethambutol. |
| Date |
2020-06-22 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s61w10bn |
| Setname |
ehsl_novel_lee |
| ID |
1578868 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s61w10bn |
