Ocular toxicity of ethambutol

RYC Chan, AKH Kwok
Department of Ophthalmology, Hong Kong Sanatorium and Hospital, Happy Valley, Hong Kong

OBJECTIVE. To review the literature on ocular toxicity of ethambutol—its background, clinical presentation, toxicity characteristics, management, monitoring, and preventive measures.

DATA SOURCES. Literature search of Medline from 1962 to May 2005.

STUDY SELECTION. All related literature in English using the search formula: (ethambutol OR myambutol) AND (eye* OR ophthal* OR ocular) AND (adverse OR toxic).

DATA EXTRACTION. All information was collected and analysed by authors.

DATA SYNTHESIS. Ethambutol hydrochloride is a commonly used first-line anti-tuberculous agent. Although rare, ocular toxicity in the form of optic neuritis (most commonly retrobulbar neuritis) has been well documented since its first use in the 1960s. Classically described as dose- and duration-related and reversible on therapy discontinuation, reversibility of optic neuritis remains controversial. International guidelines on prevention and early detection of ethambutol-induced ocular toxicity have been published. Nonetheless, opinion of the clinical effectiveness of regular vision tests to enable early detection of toxicity is divided.

CONCLUSIONS. The course of ethambutol-induced ocular toxicity is unpredictable. Measures to ensure a high level of awareness in medical staff and patients of this potential adverse effect appear to be the best current preventive method. Classified by the World Health Organization as a place with an intermediate tuberculosis burden and good health infrastructure, Hong Kong is in a good position to examine the unanswered questions about ethambutol-induced ocular toxicity.

Hong Kong Med J 2006;12:56-60

Key words: Drug toxicity; Ethambutol; Eye