Ethambutol in tuberculosis.

Ethambutol gained rapid acceptance as a substitute for PAS in tuberculosis therapy because of improved patient tolerance and convenience of administration. Ocular toxicity was recognized early on but was thought to be a problem only at higher dosages. There have, however, been a number of reports of serious visual impairment on conventional dosage, with permanent blindness in some cases, and painfully slow recovery in others. The precise mechanism for the optic neuritis is not clear, and toxicity is difficult to predict in the individual patient. Ethambutol appears to contribute only marginally to modern short course regimens and should be replaced with a less toxic agent.