Chemical structure of ethambutol (top) and photo of ethambutol crystals (bottom)
|Trade names||Myambutol, Etibi, Servambutol, others|
|Defined daily dose||1,200 mg (by mouth)|
1,200 mg (parenteral)
|Elimination half-life||3–4 hours|
|Chemical and physical data|
|Molar mass||204.314 g·mol−1|
|3D model (JSmol)|
Ethambutol (EMB, E) is a medication primarily used to treat tuberculosis. It is usually given in combination with other tuberculosis medications, such as isoniazid, rifampicin and pyrazinamide. It may also be used to treat Mycobacterium avium complex, and Mycobacterium kansasii. It is taken by mouth.
Common side effects include problems with vision, joint pain, nausea, headaches, and feeling tired. Other side effects include liver problems and allergic reactions. It is not recommended in people with optic neuritis, significant kidney problems, or under the age of five. Use during pregnancy or breastfeeding has not been found to cause harm. In the United States the FDA has raised concerns about eye issues in the baby if used during pregnancy. Ethambutol is believed to work by interfering with the bacteria's metabolism.
Ethambutol was discovered in 1961. It is on the World Health Organization's List of Essential Medicines. Ethambutol is available as a generic medication. The wholesale cost in the developing world is about US$2.58–4.73 per month. In the United States it costs US$100–200 per month.
- Optic neuritis (hence contraindicated in children below six years of age)
- Red-green color blindness People taking ethambutol should be monitored for changes in visual acuity and color discrimination.
- Vertical nystagmus
- Milk skin reaction
Mechanism of action
Ethambutol is bacteriostatic against actively growing TB bacilli. It works by obstructing the formation of cell wall. Mycolic acids attach to the 5'-hydroxyl groups of D-arabinose residues of arabinogalactan and form mycolyl-arabinogalactan-peptidoglycan complex in the cell wall. It disrupts arabinogalactan synthesis by inhibiting the enzyme arabinosyl transferase. Disruption of the arabinogalactan synthesis inhibits the formation of this complex and leads to increased permeability of the cell wall.
It is well absorbed from the gastrointestinal tract and well distributed in body tissues and fluids. 50% is excreted unchanged in urine.
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