Isoniazid

Isoniazid is an antitubercular drug that is bactericidal against Mycobacterium tuberculosis. It inhibits the synthesis of mycoloic acids in susceptible bacteria which results in loss of acid-fastness and disruption of bacterial cell wall. At therapeutic levels, it is bactericidal against actively growing intracellular and extracellular M. tuberculosis organisms.

• Active tuberculosis disease
• Latent tuberculosis infection

Adult Dose (Oral):

• Active TB: 5 mg/kg PO qDay (max 300 mg/day) OR 15 mg/kg (max 900 mg) 1-3 times/week
• Latent TB (>30 kg): 300 mg PO qDay x 9 months
• Used in multi-drug regimen with rifampin, pyrazinamide, and ethambutol

Child Dose (Oral):

• Active TB: 10-15 mg/kg PO qDay (max 300 mg/day) OR 20-30 mg/kg (max 900 mg) 2 times/week
• Latent TB: 10-15 mg/kg PO qDay (max 300 mg/day)

Common Side Effects:

• Peripheral neuropathy (tingling and numbness of feet and hand)
• Increased liver enzymes
• Hepatitis (viral infection of liver)
• Jaundice

Others: Seizures, mental health problems, optic neuritis (may cause loss of vision)

Precautions:

• Isoniazid may affect your ability to drive (seizures, mental problems, optic neuritis)
• Inform doctor if signs of jaundice (yellowing of eyes or skin, dark urine, stomach pain, joint pain)
• Regular liver function monitoring required
• Avoid alcohol (additional adverse effects on liver)
• Take vitamin B6 supplement (to prevent peripheral neuropathy)
• Not recommended in severe liver disease

Contraindications:

• Acute liver disease or history of hepatic damage during INH therapy
• Hypersensitivity

Drug Interactions:

• Inhibits hepatic metabolism of antiepileptics, benzodiazepines, theophylline, disulfiram
• Increases metabolism of enflurane (potentially nephrotoxic fluoride levels)
• Increases concentrations and toxicity of clofazimine, cycloserine, warfarin
• Reduced absorption with Al-containing antacids
• Increased risk of peripheral neuropathy with zalcitabine and stavudine

Food Interactions: Consuming alcohol while taking Isoniazid may cause flushing, increased heart beat, nausea, thirst, chest pain and low blood pressure (Disulfiram reaction); avoid tyramine-rich foods (cheese, smoked fish, meats, some beers).

Use in Pregnancy: May be unsafe; animal studies have shown harmful effects; doctor will weigh benefits and risks.

Use in Lactation: Safe during breastfeeding; does not pass into breastmilk in significant amount and is not harmful to baby.

Renal Impairment: Safe in kidney disease; no dose adjustment recommended; however severe renal impairment may require dose reduction.

Hepatic Impairment: Caution in liver disease; dose adjustment may be needed; not recommended in severe liver disease.

Overdose: Nausea, vomiting, dizziness, blurred vision, confusion, seizures, coma; gastric lavage, activated charcoal; pyridoxine administration (to prevent seizures); hemodialysis may be effective.