Myambutol (Ethambutol)

Ethambutol is used in antitubercular regimens targeting Mycobacterium tuberculosis infection.

• Pulmonary tuberculosis: contributes to bacterial clearance when combined with other first‑line agents.
• Extrapulmonary tuberculosis: aids in eradication of disseminated infection as part of multidrug therapy.
• Multidrug‑resistant TB (as part of a regimen): provides an additional mechanism of action to strengthen treatment outcomes.

• Ethambutol inhibits the arabinosyl transferase enzyme involved in the polymerization of arabinogalactan, a key component of the mycobacterial cell wall. By blocking this step, the drug impairs cell wall synthesis, leading to increased bacterial susceptibility and eventual death of Mycobacterium tuberculosis when used with other antitubercular agents.

Ethambutol may cause a range of adverse reactions, which are categorized by frequency.

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Vomiting: occasional emesis.
• Abdominal pain: discomfort in the upper abdomen.
• Loss of appetite: reduced desire to eat.
• Rash: mild skin erythema.
• Fever: low‑grade temperature elevation.

Serious or Rare Side Effects

• Optic neuritis: visual acuity loss or color‑vision disturbances.
• Severe hypersensitivity: angioedema or anaphylactic reactions.
• Hepatic dysfunction: elevated liver enzymes or hepatitis.
• Seizures: rare neurologic events.
• Peripheral neuropathy: tingling or numbness in extremities.
• Acute kidney injury: reduced renal function in susceptible patients.

When prescribing Ethambutol, clinicians should consider several safety measures.

• Renal impairment: assess kidney function and adjust dosing if necessary.
• Visual monitoring: obtain baseline eye examination and repeat periodically during therapy.
• Pregnancy: use only if the potential benefit justifies the potential risk to the fetus.
• Hepatic dysfunction: monitor liver enzymes regularly.
• Drug resistance: ensure adherence to combination therapy to prevent emergence of resistant strains.
• Store at ambient temperature: keep in the original container, protect from moisture and light.

Ethambutol can interact with other medicines, requiring attention to the interaction strength.

Major Interactions (Avoid)

• Isoniazid: may increase risk of optic neuritis.
• Rifampicin: can reduce ethambutol plasma concentrations, potentially lowering efficacy.
• Streptomycin: additive ototoxicity when used together.

Moderate Interactions (Monitor Closely)

• Pyrazinamide: combined use may heighten hepatotoxic potential.
• Antiretroviral agents (e.g., zidovudine): monitor for overlapping toxicities.
• Diuretics: may affect renal clearance of ethambutol, requiring renal function checks.