Myambutol (Ethambutol Hydrochloride)

Ethambutol is an antitubercular agent used in combination regimens targeting Mycobacterium tuberculosis infections.

• Pulmonary tuberculosis: contributes to bacterial clearance when combined with other first‑line drugs.
• Extrapulmonary tuberculosis: aids in treating disease sites such as lymph nodes, pleura, or meninges as part of multidrug therapy.
• Miliary tuberculosis: provides bacteriostatic activity across disseminated infection when used in standard combination protocols.

• Ethambutol inhibits the arabinosyl transferase enzyme involved in arabinogalactan synthesis, a key component of the mycobacterial cell wall. By blocking this pathway, the drug reduces cell wall integrity, leading to a bacteriostatic effect against Mycobacterium tuberculosis. The inhibition is selective for mycobacteria, allowing it to be used safely in combination with other antitubercular agents.

Ethambutol may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Visual disturbances (blurred vision, color vision changes)
• Nausea
• Vomiting
• Abdominal pain
• Headache
• Rash

Serious or Rare Side Effects

• Optic neuritis leading to permanent vision loss
• Severe allergic reactions including anaphylaxis
• Hepatic dysfunction (elevated transaminases, hepatitis)
• Peripheral neuropathy
• Stevens‑Johnson syndrome or toxic epidermal necrolysis
• Severe dizziness or loss of coordination

When prescribing Ethambutol, clinicians should observe several precautionary measures to minimize risk.

• Baseline visual assessment: perform ophthalmologic exam before therapy and monitor periodically.
• Renal function monitoring: adjust dose in patients with impaired clearance.
• Hepatic impairment: use with caution and monitor liver enzymes.
• Known hypersensitivity: avoid in patients with documented allergy to ethambutol.
• Elderly patients: start at lower dose and observe for toxicity.
• Store at room temperature: keep in original packaging, protect from moisture and direct sunlight.

Ethambutol can interact with several medicines, altering its efficacy or safety profile.

Major Interactions (Avoid)

• Isoniazid: increased risk of optic neuritis when combined.
• Rifampicin: reduces ethambutol plasma concentrations, potentially decreasing effectiveness.
• Streptomycin: heightened neurotoxic potential when used together.

Moderate Interactions (Monitor Closely)

• Pyrazinamide: may increase hepatotoxic risk.
• Fluoroquinolones: additive risk of tendon disorders.
• Antiretroviral agents (e.g., protease inhibitors): may affect drug levels.
• Diuretics: can exacerbate electrolyte disturbances.
• Vitamin supplements (pyridoxine): monitor for overlapping toxicity.