C. diff Risk


Oral Bioavailability


Approximate Cost


Spectrum Of Activity


Once-Daily Therapy
5 mg/kg/dose (usual dose: 300 mg) once daily

Altnerate options available, including 3 times weekly therapy.

Please consult ID

CrCl >50 mL/min

  • 300 mg PO Q24h

CrCl <50 mL/min or Dialysis

  • No change

There are no dosage adjustments; however, use with caution, may accumulate and additional liver damage may occur in patients with preexisting liver disease.

Contraindicated in patients with acute liver disease or previous isoniazid-associated hepatic injury.

Treatment with isoniazid for latent tuberculosis infection should be deferred in patients with acute hepatic diseases.

General Information

Common Usage

  • Active Tuberculosis

  • ¬†Latent Tuberculosis

  • ¬†Nontuberculous mycobacterium (M. kansasii)

Drug Monitoring


  • ¬†LFTs in patients with underlying liver disease or comorbidities

  • For ALT or AST >3 times the ULN: discontinue or temporarily withhold treatment.


  • Monitor for signs of hepatic dysfunction

Adverse Effects

>10%: Hepatic: Increased serum transaminases (mild and transient 10% to 20%)

Major Interactions

Multiple CYP Interactions