ISONIAZID

Indications & Dose:

Treatment and prophylaxis of tuberculosis; severe tremor in patients with multiple sclerosis* 

DOSE

Adult:

• Treatment: PO 5 mg/kg/day (up to 300 mg total) in a single dose; use in conjunction with other effective antituberculosis agents; duration of treatment 6 mo-2 yr

• Disseminated disease: PO 10 mg/kg/day in 1-2 divided doses 

• Prophylaxis: PO 300 mg qd

Child: Treatment: PO or IM 10-20 mg/kg/day (up to 300 mg total) in 1-2 divided doses

 • Prophylaxis: PO or IM 10 mg/kg/day qd, do not exceed 300 mg/ day 

Contraindications:

Previous isoniazid-associated hepatic injury, acute liver disease

Side Effects:

CNS: Fever, memory impairment, peripheral neuropathy, seizures, toxic encephalopathy, toxic psychosis

EENT: Optic neuritis and atrophy

GI: Epigastric distress, hepatotoxicity (mild and transient elevation of serum transaminases in 10%-20% does not require discontinuation; progressive liver damage rare in patients <20 yr, but is seen in as many as 2.3% of those >50 yr), nausea, vomiting

HEME: Agranulocytosis; eosinophilia, hemolytic, sideroblastic, or aplastic anemia; thrombocytopenia

METAB: Gynecomastia, hyperglycemia, hypocalcemia, hypophosphatemia, metabolic acidosis, pellagra, pyridoxine deficiency

SKIN: Skin eruption, vasculitis

MISC.: Rheumatic; syndrome, systemic lupus erythematosus-like syndrome 

Cautions:

Precautions:

Active chronic liver disease, severe renal dysfunction, malnutrition, slow acetylators, elderly, diabetes, alcoholics (increased risk of peripheral neuropathy

Interaction:

Drugs

Acetaminophen: Increased acetaminophen concentrations, potential for hepatotoxicity

Antacids: Reduced plasma isoniazid concentrations

Carbamazepine: Increased serum carbamazepine concentrations, toxicity may occur

Corticosteroid s: Reduced plasma concentrations of isoniazid

Cycloserine: Increased potential for CNS toxicity

Diazepam triazolam: Increased concentrations of these drugs

Disulfiram: Adverse mental changes and coordination problem

Ethanol: Higher incidence of isoniazid-induced hepatitis in alcoholics

Phenytoin: Predictable increases in serum phenytoin concentrations, toxicity possible

Rifampin: Increased hepatotoxicity of isoniazid in some patients; more common with slow acetylators of isoniazid, and or preexisting liver disease

Theophylline: Increased theophylline concentrations, toxicity possible

Valporic acid: Increased valproic acid concentration possible

Warfarin: Potential for enhanced hypoprothrombinemic response to warfarin 

Warnings:

Adverse Effects:

Lactations:

The American Thoracic Society recommends use of isoniazid for tuberculosis during pregnancy; excreted in breast milk; women can safely breast feed their infants while taking isoniazid if the infant is periodically examined for signs and symptoms of peripheral neuritis or hepatitis 

Special Precautions:

Counselling:

Side Effects Or Adverse Reactions:

Patient And Carer Advice: