Isoniazid (INH)

Category:

• Miscellaneous

Description:

• Antituberculosis agent

Indications:

• Treatment and prophylaxis of tuberculosis

• Severe tremor in patients with multiple sclerosis (non-FDA approved)

Contraindications:

• Previous isoniazid-associated hepatic injury

Precautions:

• Pregnancy category C; safe to use in pregnancy; safe to breast feed if infant periodically examined for signs and symptoms of peripheral neuritis or hepatitis

• Active chronic liver disease, severe renal dysfunction, malnutrition

• Slow acetylators, elderly, diabetes, alcoholics (increased risk of peripheral neuropathy)

Adverse Reactions (Side Effects):

• CNS: fever, memory impairment, peripheral neuropathy, seizures, toxic encephalopathy, toxic psychosis

• EENT: optic neuritis and atrophy

• GI: epigastric distress, hepatotoxicity, nausea, vomiting

• HEME: agranulocytosis, eosinophilia, hemolytic, sideroblastic, or aplastic anemia; thrombocytopenia

• METAB: gynecomastia, hyperglycemia, hypocalcemia, hypophosphatemia, metabolic acidosis, pellegra, pyridoxine deficiency

• SKIN: skin eruptions, vasculitis

• MISC: rheumatic syndrome, systemic lupus erythematosis-like syndrome

Dosage:

Administered orally

• Adult:            

  • Treatment: PO 5 mg/kg/day (up to 300mg total) in a single dose; use in conjunction with other effective antituberculosis agents; duration of treatment 9 months to 2 years

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

  • Prophylaxis: PO 300mg daily

• Child:            

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

  • Prophylaxis: PO 10 mg/kg/day every day, not to exceed 300mg daily

Drug interactions:

• Disulfuram: adverse mental changes and coordination problems

• Acetaminophen, carbamazepine, cycloserine, theophylline, valproic acid: increased concentrations, possibly to toxic levels

• Rifampin: incresed hepatotoxicity of isonizid in some patients

• Ethanol: increased incidence of isoniazid-induced hepatitis in alcoholics