What is the relationship between Ethambutol (Ethambutol hydrochloride) and vision loss?

From the Guidelines

Ethambutol can cause vision loss as a side effect, which typically manifests as decreased visual acuity, color vision defects, and visual field defects, and patients should be monitored regularly for these symptoms, especially when taking higher doses or for extended periods, as stated in the 2019 study 1.

Key Points

• The risk of vision loss with ethambutol increases at higher doses, with approximately 1-5% of patients taking standard doses experiencing this side effect, as reported in the 2007 study 1.
• Regular eye examinations are recommended before starting treatment and monthly during therapy, especially for patients on higher doses (>15-20 mg/kg/day) or those taking it for extended periods, as suggested in the 2016 study 1.
• The vision loss is usually reversible if the medication is promptly discontinued, but permanent damage can occur if ethambutol is continued despite visual symptoms, as noted in the 2019 study 1.
• Patients with renal impairment are at higher risk due to decreased drug clearance, so dose adjustments are necessary in these cases, as stated in the 1998 study 1.
• Alternative tuberculosis medications may be considered for patients with pre-existing visual problems, as recommended in the 2003 study 1.

Recommendations

• Patients taking ethambutol should be educated about the potential side effects of the medication and encouraged to self-report changes in vision, as suggested in the 2016 study 1.
• Healthcare providers should monitor patients regularly for signs of ocular toxicity, particularly visual impairment, and discontinue ethambutol if this is detected, as recommended in the 2019 study 1.
• The dose of ethambutol should be adjusted based on the patient's renal function and body weight, as stated in the 2007 study 1.
• Alternative medications should be considered for patients with pre-existing visual problems or those who experience visual symptoms while taking ethambutol, as recommended in the 2003 study 1.

From the FDA Drug Label

ETHAMBUTOL HCl may produce decreases in visual acuity, including irreversible blindness, which appear to be due to optic neuritis. Optic neuropathy including optic neuritis or retrobulbar neuritis occurring in association with ethambutol therapy may be characterized by one or more of the following events: decreased visual acuity, scotoma, color blindness, and/or visual defect Recovery of visual acuity generally occurs over a period of weeks to months after the drug has been discontinued.

Vision Loss with Ethambutol:

• Ethambutol may cause decreases in visual acuity, including irreversible blindness, due to optic neuritis.
• Optic neuropathy may occur, characterized by decreased visual acuity, scotoma, color blindness, and/or visual defect.
• Recovery of visual acuity generally occurs over a period of weeks to months after the drug has been discontinued 2.
• The effect of ethambutol on vision may be related to dose and duration of treatment, and is generally reversible when administration of the drug is discontinued promptly, but irreversible blindness has been reported 2.

From the Research

Ethambutol-Induced Vision Loss

• Ethambutol is a first-line chemotherapeutic agent used in combination with other drugs for the treatment of tuberculosis, which can cause optic neuritis and vision loss as a rare side effect 3.
• The vision loss caused by ethambutol is dose- and duration-dependent, and can lead to permanent vision loss by inducing optic neuropathy 4.
• Studies have shown that ethambutol-induced optic neuropathy can occur in approximately 1% of patients taking ethambutol at the WHO recommended doses, though the risk increases substantially with increased dose 5.

Clinical Findings and Management

• Patients with ethambutol-induced optic neuropathy may present with painless diminished vision in both eyes, and may have cecocentral scotomas in the visual field 3.
• The management of ethambutol-induced optic neuropathy involves stopping the drug and starting supportive therapy, such as oral prednisone, zinc, and vitamin B complex 3.
• Regular screening by an ophthalmologist, including formal visual field testing, is recommended for all patients on ethambutol 5.

Long-Term Effects and Screening

• Long-term follow-up of patients with ethambutol toxicity has shown that signs of ethambutol toxicity may remain or worsen years after discontinuation, even in the absence of patient symptoms and with normal visual acuity and visual fields 6.
• Visual acuity, color vision, and visual evoked potential are sensitive and sustainable tools that can be implemented in regular screening for ethambutol toxicity 7.
• A collaborative approach is necessary to establish screening protocols and prevent ethambutol-induced toxic optic neuropathy 7.