Ethambutol

Agent: ethambutol (EMB)

Ethambutol is a first-line drug for the treatment of both active tuberculosis and MAC infections. It inhibits production of arabinogalactan, a component of the mycobacterial cell wall. Like pyrazinamide,  ethambutol is principally used in the initial 4-drug phase of active tuberculosis, but it is usually given for the duration of MAC therapy.

Spectrum

M. tuberculosis,  M. avium-intracellulare complex, M. kansasii.

Adverse Effects

The characteristic adverse effect of ethambutol is optic neuritis, often manifesting as decreased visual acuity and the inability to differentiate red from green. It is dependent on both the dose and duration of therapy and generally reversible, and monitoring is required to detect this problem. Use of ethambutol in children younger than 5 years is not recommended, because these children are gen-erally not able to reliably perform the vision tests needed for monitoring. Rash and drug fever occur uncommonly.

Important Facts

• Ethambutol is very well tolerated, and it is one of the few tuberculosis drugs that is not associated with hepatotoxicity.

• Ethambutol can be used as a substitute for rifampin in patients who are unable to take this medication during the continuation phase  (after 2 months) of active tuberculosis therapy.  However, the duration of therapy has to be ex-tended relative to what it would be with rifampin and isoniazid.

• Ethambutol is one of the primary first-line drugs (along with a macrolide and rifabutin)  for treating MAC infections.

 What It’s Good For

First-line therapy for both active tuberculosis and MAC infections. Second-line therapy in patients unable to tolerate rifampin during the continuation phase.

Don’t Forget!

Want an easy way to remember that ethambutol causes optic neuritis? Just remember: for Ethambutol, the Eyes have it!

References

Gallagher ,J.C. and MacDougall ,c. (2012). Antibiotics Simplified. Second Edition. Jones & Bartlett Learning, LLC.