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ANTIINFECTIVES FOR SYSTEMIC USE › ANTIMYCOBACTERIALS › DRUGS FOR TREATMENT OF TUBERCULOSIS › Hydrazides
isoniazid
J04AC01
Forms & Strengths
- Tablet: 100 mg
- Tablet: 300 mg
- Syrup: 50 mg/5 mL
- Injection: 100 mg/mL in 10 mL vials
Adult Dosing
- Active tuberculosis: 5 mg/kg (up to 300 mg) orally or IV once daily, or 15 mg/kg (up to 900 mg) 2 to 3 times weekly
- Latent tuberculosis infection: 300 mg orally once daily for 9 months (preferred) or 600 mg twice weekly for 9 months; alternative 900 mg twice weekly for 3 months (with rifapentine)
Pediatric Dosing
- Active tuberculosis: 10 to 15 mg/kg (maximum 300 mg) orally or IV once daily, or 20 to 30 mg/kg (maximum 900 mg) twice weekly
- Latent tuberculosis infection: 10 to 15 mg/kg (maximum 300 mg) orally once daily for 9 months
Indications
- Treatment of all forms of tuberculosis caused by Mycobacterium tuberculosis (in combination with other agents)
- Prophylaxis/Latent tuberculosis infection in high-risk individuals
Mechanism of Action
- Inhibits synthesis of mycolic acids, essential components of the mycobacterial cell wall
- Bactericidal against actively dividing tubercle bacilli
Contraindications
- Previous acute chemical hepatitis associated with isoniazid
- Previous severe adverse reactions such as drug-induced fever, chills, or arthritis
- Acute liver disease of any etiology
Adverse Reactions
- Elevated liver enzymes and drug-induced hepatitis
- Peripheral neuropathy (associated with pyridoxine deficiency)
- Central nervous system toxicity (dizziness, psychoses, seizures)
- Hypersensitivity reactions (rash, fever)
- Hematologic abnormalities (agranulocytosis, hemolytic anemia, thrombocytopenia)
Drug Interactions
- CYP inhibitors: inhibits CYP1A2, CYP2C19, and CYP2C9, increasing plasma levels of agents like phenytoin, carbamazepine, and warfarin
- Antacids (aluminum hydroxide): decrease absorption and bioavailability of isoniazid
- Alcohol: increases the risk of hepatotoxicity
- Pyridoxine (vitamin B6): co-administration prevents or treats peripheral neuropathy
Curated Content: Needs Vetting Before Put to Clinical Use