Ocular toxicity from ethambutol: a review of four cases and recommended precautions

To document the clinical and demographic features of cases of ethambutol ocular toxicity, to review the literature on this subject and to critically review current guidelines for ethambutol administration.

Cases of ocular toxicity from ethambutol were sought retrospectively at Green Lane and Wellington Hospitals between 1992 and 1995. The records of cases identified were examined.

Four subjects with tuberculosis developed ocular toxicity 2 1/2, 7 1/2, 8 and 12 months after starting ethambutol. Normal visual acuity returned in three cases; one patient has severe, permanent visual impairment. Language difficulties were present in three subjects.

Impaired communication was potentially very important in this series. Special care is needed in educating patients about ethambutol. We propose additional recommendations: 1. the usual daily dose of ethambutol should be 15 mg/kg/day, not 25 mg/kg/day; using 25 mg/kg/day (or lesser doses in the presence of renal impairment) should prompt regular formal ophthalmological evaluation (e.g. monthly) in cases with comprehension or communication difficulties; 3. both ethambutol and isoniazid should be stopped immediately if severe optic neuritis occurs. Isoniazid should be stopped if less severe optic neuritis does not improve within six weeks after stopping ethambutol.