Products
Isoniazid is commercially available in tablet form (eg, Isoniazid Labatec, combination products).
Structure and properties
Isoniazid (C6H7N3O, Mr = 137.1 g/mol) exists as a white crystalline powder or colorless crystals and is readily soluble in water. It is also known as isonicotinylhydrazine (INH).
Effects
Isoniazid (ATC J04AC01) has bacteriostatic to bactericidal properties against . The effects are due to inhibition of the synthesis of mycolic acids, which are found in the bacterial cell wall.
Indications
For the treatment of tuberculosis (combination therapy).
Dosage
According to the SmPC. Tablets are taken once to three times daily, fasting, at least half an hour before or two hours after a meal. Isoniazid should be combined with vitamin B6 to prevent neurologic side effects.
Contraindications
- Hypersensitivity
- Peripheral neuritis
- Severe bleeding tendency
- Severe liver disease
Full precautions can be found in the drug label.
Interactions
Isoniazid is acetylated and hydrolyzed to isonicotinic acid. Drug-drug interactions have been described with the following agents, among others: Barbiturates, phenytoin, carbamazepine, primidone, rifampicin, valproic acid, acetaminophen, ketoconazole, theophylline, disulfiram, alcohol, antacids, and levodopa. Foods high in tyramine or histamine should be avoided during treatment.
Adverse effects
The most common possible adverse effects include polyneuritis (when taken without vitamin B6), indigestion, elevation of liver enzymes, hepatitis, facial flushing, pruritus, skin rash, and eye redness. During treatment, bacteria may become resistant to the drug. Therefore, isoniazid is combined with other tuberculostatics.
