Isoniazid (Isonicotinic Acid Hydrazide; INH)

A to Z Drug Facts

(eye-so-NYE-uh-zid)

Nydrazid, Isoniazid,  Dom-Isoniazid, Isotamine, PMS-Isoniazid

Class: Anti-infective/Antitubercular

 Action Interferes with lipid and nucleic acid biosynthesis in actively growing tubercle bacilli.

 Indications Treatment of all forms of tuberculosis. Unlabeled use(s): Improvement of severe tremor in multiple sclerosis.

 Contraindications Previous isoniazid-associated hepatic injury, drug fever, chills, or arthritis; acute liver disease.

 Route/Dosage

Tuberculosis

ADULTS: PO/IM 5 mg/kg/day as single daily dose (max 300 mg/day). INFANTS & CHILDREN: PO/IM 10 to 20 mg/kg/day in single daily dose (max 300 mg/day).

Multiple Sclerosis

ADULTS: PO/IM 300 to 400 mg/day, increased over 2 wk to 20 mg/kg/day.

 Interactions

Aluminum salts: May reduce oral absorption of isoniazid; give isoniazid 1 to 3 hr before aluminum salts. Carbamazepine: May result in carbamazepine toxicity or isoniazid hepatotoxicity. Monitor carbamazepine concentrations and liver function. Disulfiram: May result in increased incidence of CNS effects (eg, coordination difficulties, confusion, irritability, aggressiveness). Enflurane: May result in high-output renal failure in rapid acetylators. Monitor renal function. Hydantoins: May increase serum hydantoin levels. Rifampin: May result in higher rate of hepatotoxicity.

 Lab Test Interferences None well documented.

 Adverse Reactions

CNS: Peripheral neuropathy; convulsions; toxic encephalopathy; optic neuritis and atrophy; memory impairment; toxic psychosis. DERM: Morbilliform, maculopapular, purpuric or exfoliative skin eruptions. GI: Nausea; vomiting; epigastric distress. HEMA: Agranulocytosis; hemolytic, sideroblastic or aplastic anemia; thrombocytopenia; eosinophilia. HEPA: Hepatotoxicity, including elevated serum transaminase levels, bilirubinemia, bilirubinuria, jaundice, severe and sometimes fatal hepatitis. META: Pyridoxine deficiency; pellagra; hyperglycemia; metabolic acidosis; hypocalcemia; hypophosphatemia. OTHER: Gynecomastia; rheumatic syndrome; systemic lupus erythematosus-like syndrome; local irritation at IM injection site.

 Precautions

Pregnancy: Safety undetermined. Lactation: Excreted in breast milk. Hepatic impairment: Common prodromal symptoms of hepatotoxicity include anorexia, nausea, vomiting, fatigue, malaise, and weakness. Patients with acute hepatic disease should have preventive tuberculosis treatment deferred. Incidence of hepatic reaction increases in patients > 50 yr. Hypersensitivity: Discontinue drug at first sign of hypersensitivity reaction. Restart only after symptoms have cleared. Pyridoxine administration: Prophylactic concomitant administration of pyridoxine (6 to 50 mg/day) is recommended in malnourished patients and those predisposed to neuropathy (eg, alcoholics, diabetics). Renal impairment: Monitor patients with severe renal dysfunction carefully.

 Administration/Storage

• Oral form available in tablet and syrup forms.
• Administer oral medication on empty stomach at least 1 hr before or 2 hr after meals.
• If GI irritation becomes problem, drug may be administered with food, although food decreases absorption of drug.
• Antacids may be given 1 hr before administration.
• Store at room temperature and protect from moisture.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies.
• Assess mycobacterial studies and susceptibility tests before and periodically throughout therapy to detect possible resistance.
• Evaluate hepatic function studies before and monthly during therapy (SGOT [AST], SGPT [ALT]) and serum bilirubin.
• Assess patient for adverse reactions: GI distress, peripheral neuritis, optic neuritis, or hypersensitivity reactions.
• If nausea, vomiting, anorexia, or diarrhea develop, obtain order for antiemetic or antidiarrheal medication and assess for hepatotoxicity.
• Take safety precautions if patient experiences adverse CNS symptoms such as confusion or incoordination.

 Patient/Family Education

• Teach patient and family the name, dose, action, and side effects of isoniazid.
• Advise patient to minimize daily alcohol consumption while taking isoniazid because of the increased risk of hepatitis.
• Instruct patient to report the following symptoms to physician: Weakness; fatigue; loss of appetite; nausea and vomiting; yellowing of skin or eyes; darkening of urine; numbness or tingling in hands or feet.
• Emphasize to patient that treatment will be lengthy and that patient must complete entire course of therapy. Relapse of tuberculosis is higher if chemotherapy is discontinued prematurely.
• Advise patient to return for laboratory follow-up.
• Caution patient not to perform activities that require mental alertness if adverse CNS symptoms occur.

Books@Ovid
Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts