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ANTIINFECTIVES FOR SYSTEMIC USE › ANTIMYCOBACTERIALS › DRUGS FOR TREATMENT OF TUBERCULOSIS › Combinations of drugs for treatment of tuberculosis
ethambutol and isoniazid
J04AM03
Forms & Strengths
- Fixed-dose combination tablet: Isoniazid 150 mg / Ethambutol HCl 400 mg
- Fixed-dose combination tablet: Isoniazid 300 mg / Ethambutol HCl 800 mg
Adult Dosing
- Active tuberculosis: Dosing based on weight and specific treatment guidelines, typically administered daily or intermittently.
- Usually calculated as part of multi-drug regimens using weight-tiered dosing for each component.
Pediatric Dosing
- Safety and efficacy in pediatric patients depend on individual component dosing per body weight.
- Fixed-dose combination tablets are generally less preferred in small children due to difficulty in precise weight-based titration.
Indications
- Treatment of active tuberculosis caused by susceptible strains of Mycobacterium tuberculosis (typically as part of initial multi-drug regimens).
Mechanism of Action
- Isoniazid inhibits mycolic acid synthesis, disrupting the mycobacterial cell wall.
- Ethambutol inhibits arabinosyl transferases, disrupting cell wall arabinogalactan biosynthesis.
Contraindications
- Known hypersensitivity to isoniazid, ethambutol, or any component of the formulation.
- Acute liver disease or severe preexisting hepatic impairment.
- Previous history of isoniazid-induced hepatic injury or severe adverse reactions.
- Optic neuritis (contraindication for ethambutol component unless clinical judgment dictates otherwise).
Adverse Reactions
- Hepatotoxicity (elevated transaminases, hepatitis, fatal liver necrosis)
- Peripheral neuropathy (associated with isoniazid, mitigated by pyridoxine)
- Optic neuritis (decreased visual acuity, red-green color blindness, associated with ethambutol)
- Gastrointestinal distress (nausea, vomiting, abdominal pain)
- Hyperuricemia and acute gout attacks
- Hypersensitivity reactions (rash, fever)
Drug Interactions
- Antacids (aluminum hydroxide) decrease absorption of isoniazid and ethambutol.
- Disulfiram combined with isoniazid can cause neurologic coordination changes and acute toxic psychosis.
- Phenytoin metabolism is inhibited by isoniazid, leading to increased phenytoin toxicity.
- Rifampin co-administration may alter serum concentrations; monitor liver function closely when used in combination regimens.
Curated Content: Needs Vetting Before Put to Clinical Use