Even lower doses of Ethambutol can Induce Optic Neuropathy, suggests study

The site of tuberculosis infection, daily dose, ethambutol (EMB) treatment duration, onset, and type of ocular symptoms were recorded. We performed regression analyses to investigate the univariate and multivariable associations with different variables. Results: Of the 1676 patients who received ethambutol for TB treatment, 987 had an ophthalmological symptom unrelated to EON, and 13 developed EON (incidence =0.28%). Demographic and clinical variables considered were age, gender, race/ethnicity, body mass index (BMI), and diabetes mellitus status.

Examples of current infection information were chronic HIV and other comorbidities uniquely associated with renal function site/type treatment specific dose/duration ethambutol. Longer treatment duration significantly correlates with greater thickness of the left temporal retinal nerve fibre layer (RNFL) and thicker average RNFL.

Increased peripapillary retinal nerve fibre layer (pRNFL) thickness on the left nasal RNFL scan was significantly correlated with ethambutol tablets (or count) (p=0.027). The findings indicate that ethambutol toxicity is indeed dose and duration-dependent, evidenced by the relationship between prolonged treatment and increased RNFL thickness, suggesting heightened risk of visual impairment. Moreover, adverse effects were observed at even lower doses (12.3 mg/kg), reinforcing that no dose of ethambutol is entirely safe.

Reference:

Singh P, Karkhur S, Verma V (February 17, 2025) Ethambutol-Induced Optic Neuropathy: A Retrospective Study of Incidences and Risk Factors. Cureus 17(2): e79160. doi:10.7759/cureus.79160