Toxic ocular effects of ethambutol.

Ethambutol hydrochloride has been used in the treatment of tuberculosis for 25 years. Its only important adverse effect, retrobulbar neuritis, is thought to be a minor concern with conventional dosages. The author presents four cases of serious visual impairment due to ethambutol therapy. Three of the patients were receiving a maintenance dosage of 15 mg/kg per day. The fourth patient was inadvertently given 25 mg/kg per day for 4 months. After therapy with the drug was stopped, improvement was slow, with complete recovery in two cases and only minor residual changes in a third. The patient who received the higher dosage of ethambutol suffered permanent, marked impairment. Ethambutol appears to contribute little to modern short-course antituberculous regimens that include more potent agents such as isoniazid and rifampin. In view of this and the potential for serious visual impairment, alternative antituberculous agents should be considered.