NCLEX RN Practice Question # 415

isoniazid 1

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Isoniazid (INH)


  • Isoniazid is bactericidal.
  • It inhibits the synthesis of mycolic acids and acts to kill actively growing organisms in the extracellular environment.
  • It inhibits the growth of dormant organisms in the macrophages and caseating granulomas.
  • It is active only during cell division and is used in combination with other antitubercular medications.

Contraindications and cautions

  • Isoniazid is contraindicated in clients with hypersensitivity or with acute liver disease.
  • Use with caution in clients with chronic liver disease, alcoholism, or renal impairment.
  • Use with caution in clients taking nicotinic acid (niacin).
  • Use with caution in clients taking hepatotoxic medications because the risk for hepatotoxicity increases.
  • Alcohol increases the risk of hepatotoxicity.
  • Isoniazid may increase the risk of toxicity of carbamazepine (Tegretol) and phenytoin (Dilantin).
  • Isoniazid may decrease ketoconazole (Nizoral) concentrations.

Side effects

  • Hypersensitivity reactions
  • Peripheral neuritis
  • Neurotoxicity
  • Hepatotoxicity; increased liver function test levels
  • Pyridoxine (vitamin B6) deficiency
  • Irritation at injection site with intramuscular administration
  • Nausea and vomiting
  • Dry mouth
  • Dizziness
  • Hyperglycemia
  • Vision changes
  • Hepatitis


  • Assess for hypersensitivity.
  • Assess for hepatic dysfunction.
  • Assess for sensitivity to nicotinic acid.
  • Monitor liver function test results.
  • Monitor for signs of hepatitis, such as anorexia, nausea, vomiting, weakness, fatigue, dark urine, or jaundice; if these symptoms occur, withhold the medication and notify the physician.
  • Monitor for tingling, numbness, or burning of the extremities.
  • Assess mental status.
  • Monitor for visual changes, and notify the physician if they occur.
  • Assess for dizziness and initiate safety precautions.
  • Monitor complete blood count (CBC) and blood glucose levels.
  • Administer isoniazid 1 hour before or 2 hours after a meal because food may delay absorption.
  • Administer isoniazid at least 1 hour before antacids, especially those antacids that contain aluminum.
  • Administer pyridoxine as prescribed to reduce the risk of neurotoxicity.

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