Ethambutol
Ethambutol hydrochloride
Also known as: Myambutol · Etibi · CL-40882 · etambutol · ethambutoli
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of disseminated M. tuberculosis | 10-25 mg/kg PO once daily | PO | once daily | More than 9 months | 🌎 NA |
- Treatment of disseminated M. tuberculosis: Used in combination with rifampin (5-10 mg/kg PO q12-24h) and isoniazid (10-20 mg/kg PO once daily). May also add pyrazinamide (ineffective for M. bovis).
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of feline tuberculosis (resistant cases) | 15 mg/kg PO once daily | PO | once daily | Not specified | 🌎 NA |
- Treatment of feline tuberculosis (resistant cases): Considered if resistance develops to initial therapy. Used in combination with rifampin and isoniazid.
Birds
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of M. avium infections in caged birds (Protocol 1) | 20 mg/kg PO q12h | PO | q12h | 6-12 months | 🌎 NA |
| Treatment of M. avium infections in caged birds (Protocol 2) | 30 mg/kg PO once daily | PO | once daily | 6-12 months | 🌎 NA |
| Treatment of M. avium infections in caged birds (Protocol 3) | 30 mg/kg PO once daily | PO | once daily | 6-12 months | 🌎 NA |
| Avian mycobacteriosis | 30-85 mg/kg PO once daily | PO | once daily | 9-12 months | 🌎 NA |
- Treatment of M. avium infections in caged birds (Protocol 1): Used with Ciprofloxacin/Enrofloxacin, Clofazimine, and Cycloserine.
- Treatment of M. avium infections in caged birds (Protocol 2): Used with Clofazimine and Rifampin.
- Treatment of M. avium infections in caged birds (Protocol 3): Used with Ciprofloxacin/Enrofloxacin and Rifampin/Rifabutin.
- Avian mycobacteriosis: Used with Rifabutin, Clarithromycin, and Enrofloxacin.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ethambutol is a synthetic, bacteriostatic antimycobacterial agent used primarily as part of a multi-drug protocol (a "cocktail") to treat stubborn mycobacterial infections (such as M. tuberculosis, M. bovis, M. genavense, and M. avium-intracellulare complex) in dogs, cats, and birds.
Clinical Pearl: Monotherapy is strictly avoided due to the rapid development of step-wise resistance. It is typically combined with drugs like rifampin, isoniazid, enrofloxacin, or macrolides.
Important Public Health Note: Treating mycobacterial infections in veterinary medicine is highly controversial due to the significant zoonotic potential and public health risks, particularly for immunocompromised individuals in the household.
Mechanism of action
Ethambutol is active only against actively dividing mycobacteria.
Mechanistically, it inhibits the enzyme arabinosyl transferase → disrupts the synthesis of arabinogalactan → prevents the incorporation of mycolic acid into the mycobacterial cell wall.
This disruption increases cell wall permeability, which allows other antimycobacterial drugs (like rifampin or isoniazid) to penetrate the cell more effectively. It also interferes with RNA synthesis. It has no appreciable activity against other non-mycobacterial bacteria or fungi.
Safety & warnings
Contraindications
- Patients with a history of prior hypersensitivity reactions to ethambutol
Adverse effects
- Optic neuritis (decreased visual acuity, usually reversible)
- CNS degenerative changes (with prolonged use)
- Myocardial toxicity (at high doses)
- Depigmentation of the tapetum lucidum
- Bacterial or fungal overgrowth (due to prolonged multi-drug antimicrobial therapy)
Precautions
Use with caution in patients with markedly reduced renal function; dosage adjustments may be necessary. Treatment of mycobacterial infections in animals carries significant public health risks. Routine ophthalmologic exams are recommended for long-term use due to the risk of optic neuritis.
Drug interactions
Can reduce oral absorption of ethambutol; separate dosing by at least 4 hours if both are necessary
Monitoring
- Clinical efficacy
- Visual function (periodic monitoring with long-term therapy)
- Liver function
- Renal function
- CBC
- Monitor for fungal or bacterial overgrowth infections
Pharmacokinetics
Half-life
Absorption
In humans, rapidly absorbed after PO administration with bioavailability around 75%.
Distribution
Distributed widely in the body. CSF levels range from 10-50% of serum levels. Erythrocyte concentrations are about twice that of serum and serve as a depot. Volume of distribution in dogs is 3.8 L/kg.
Metabolism
About 15% of absorbed drug is hepatically metabolized to inactive metabolites.
Elimination
Majority eliminated by both tubular secretion and glomerular filtration as unchanged drug in the urine. Total body clearance in dogs is 13.2 mL/min/kg.
Overdose
Very limited veterinary information exists. In humans, acute overdoses of >10 grams have caused optic neuritis. Other adverse effects noted with human overdoses include CNS effects (confusion, visual hallucinations), abdominal pain, nausea, fever, and headache. Treatment is supportive.
Available products
Formulations
- tablets
Human-labeled
- Ethambutol HCl Tablets: 100 mg & 400 mg (scored)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store tablets below 40°C, preferably between 15-30°C, in well-closed containers.
Client information
- Public Health Warning: Mycobacterial infections (like tuberculosis) can be transmitted to humans. You are strongly encouraged to contact a physician, preferably an infectious disease specialist, for guidance, especially if there are immunocompromised individuals in the home.
- Treatment Commitment: Treatment is very prolonged (many months to over a year) and can be expensive.
- Administration: May be administered with or without food.
- Vision Monitoring: This medication can affect vision. Report any changes noted with your pet's eyes or vision (e.g., bumping into objects, altered pupil appearance) to the veterinarian immediately.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.