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

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