Isoniazid

Summary

Isoniazid is a medication used to treat tuberculosis. It can be used to treat both active and latent TB, as well as prophylactically for someone who has been exposed. Isoniazid is hepatotoxic. It can also cause peripheral neuropathy, but that can be prevented with vitamin B6 supplementation.

Key Points

• Isoniazid (Laniazid)
  • Mechanism
    • Antitubercular
      • Antimycobacterial,
        • Inhibits the synthesis of mycolic acid in the cell wall
        • Active only during cell division
      • Used in combination with other antitubercular medications
    • Weak MAOI
      • Avoid tyramine-containing food
        • Wines, aged cheeses, alcohol, cured meats (salami, sausage, etc)
      • Contraindicated with concurrent use of other MAOIs
  • Clinical Use
    • Tuberculosis
      • Indicated for both latent and active tuberculosis, as well as prophylaxis for people who have been exposed to tuberculosis
        • Usual treatment for prophylactic TB is 6-12 months
      • Patient should be instructed to complete the full course of antimicrobial therapy, even if symptoms disappear
  • SE and AR
    • Peripheral neuropathy
      • Caused by vitamin B6 deficiency, since isoniazid interferes with the activity of vitamin B6
      • Patients will often receive vitamin B6 supplementation (pyridoxine)
    • Hepatotoxicity
      • Monitor for signs of hepatitis - jaundice, nausea/vomiting, weakness, dark urine
      • Monitor liver enzymes (AST, ALT)
      • Do not give with hepatotoxic drugs (acetaminophen, alcohol, etc.)
      • Contraindicated in those with liver disease and alcoholism
    • GI distress - nausea, vomiting, constipation
      • Take on an empty stomach
      • Avoid antacids within 1 hour (decreases absorption)
    • Hyperglycemia
      • Monitor blood glucose, especially in patients with diabetes
    • Optic neuritis