Ethambutol

Key facts

• Ethambutol is an antituberculosis medicine always given together with other TB drugs, never alone, so bacteria cannot become resistant.
• It's taken once a day by mouth, usually for the first two months of a six-month or longer treatment course.
• Ethambutol can damage the optic nerve, reducing visual sharpness or the ability to tell red from green. This is usually reversible if caught early but can become permanent if the drug is continued.
• Seek urgent care for any change in vision, blurred sight, or eye pain.

What ethambutol treats

Ethambutol treats active tuberculosis, most often affecting the lungs, as part of combination therapy alongside drugs such as rifampicin, isoniazid and pyrazinamide. It is also used in some regimens for infections caused by certain nontuberculous mycobacteria. It is never used alone, because resistance develops quickly when TB bacteria are exposed to just one drug.

How ethambutol works

Ethambutol interferes with the construction of the TB bacterium's cell wall, weakening its outer structure enough to stop the bacteria multiplying. This lets the immune system, together with the other TB drugs in the regimen, clear the infection.

Before you take it

• Tell your doctor about any existing eye disease, since ethambutol's effect on vision can be harder to detect if your eyesight is already reduced.
• Kidney function affects how the drug is cleared. People with kidney impairment need a lower dose and closer monitoring.
• Ethambutol is generally avoided in children too young to reliably report vision changes, and used with caution in pregnancy.
• Have your visual acuity and colour vision tested before starting treatment and at regular intervals afterward, especially with higher doses or treatment longer than two months.

Side effects

Common effects include nausea, loss of appetite, joint discomfort, and headache.

Stop and seek urgent medical care for any of these:

• Blurred vision, reduced sharpness of sight, or trouble telling red from green.
• Eye pain or a sudden change in how colours look.
• Facial swelling, a blistering rash, or difficulty breathing.

Safety essentials

• Have your eyesight and colour vision checked before starting ethambutol and at every follow-up visit. Report any visual change immediately and stop the drug right away if one occurs, since early stopping usually allows full recovery.
• Take ethambutol exactly as prescribed alongside your other TB medicines, and complete the full course. Stopping early or skipping doses lets resistant bacteria survive.
• Tell your doctor if you have reduced kidney function, since your dose may need to be lowered.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.