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Isoniazid Dosage

Medically reviewed on October 16, 2017.

Applies to the following strengths: 100 mg/mL; 100 mg; 300 mg; 50 mg/5 mL

Usual Adult Dose for Tuberculosis - Active

Active infection: 5 mg/kg (up to 300 mg) IM or orally once a day, or 15 mg/kg (up to 900 mg) 2 to 3 times a week. Therapy is usually continued for 6 months, or 3 months beyond culture conversion (when given with rifampin and pyrazinamide).

Latent infection: 10-20 mg/kg/day orally once a day, not to exceed 300 mg/day

If isoniazid and pyrazinamide are used alone, isoniazid should be continued for 9 months. If the patient is HIV-positive, therapy should be continued for at least 9 months, or for 6 months beyond culture conversion. Longer duration of therapy should be considered for silico-, bone, and meningeal tuberculosis.

Usual Adult Dose for Tuberculosis - Prophylaxis

300 mg orally once a day or 900 mg orally 2 to 3 times a week. Isoniazid should be continued for 6 months to prevent the development of active tuberculosis in patients with no complicating factors. Patients with complicating factors such as HIV infection, diabetes, hematologic malignancy, or scars on chest X-ray should receive prophylaxis for 12 months.

Usual Adult Dose for Mycobacterium kansasii

600 to 900 mg IM or orally once a day.

Usual Pediatric Dose for Tuberculosis - Active

Oral, IM:
Infants, Children 40 kg or less, and Adolescents 14 years or less and less than 40 kg:

Treatment of active infection: CDC Recommendations: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly as part of a multidrug regimen.

Treatment of latent infection: 10 to 20 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 40 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly. Treatment duration: 9 months.

Primary prophylaxis for TB in HIV-exposed positive patients: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose twice weekly (maximum dose: 900 mg/day). Treatment duration: 9 months.

Usual Pediatric Dose for Tuberculosis - Latent

Oral, IM:
Infants, Children 40 kg or less, and Adolescents 14 years or less and less than 40 kg:

Treatment of active infection: CDC Recommendations: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly as part of a multidrug regimen.

Treatment of latent infection: 10 to 20 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 40 mg/kg/dose (maximum dose: 900 mg/day) 2 times weekly. Treatment duration: 9 months.

Primary prophylaxis for TB in HIV-exposed positive patients: 10 to 15 mg/kg/day once daily (maximum dose: 300 mg/day) or 20 to 30 mg/kg/dose twice weekly (maximum dose: 900 mg/day). Treatment duration: 9 months.

Renal Dose Adjustments

CrCl less than 10 mL/min: Reduce dose by 50%.

Liver Dose Adjustments

If liver function tests exceed 3 to 5 times the upper limit of baseline, discontinue use of isoniazid therapy and monitor until liver function tests return to baseline. Symptoms of liver toxicity include anorexia, nausea, vomiting, dark urine, icterus, rash, persistent paresthesias of the hands and feet, persistent fatigue, weakness or fever greater than 3 days duration, and right upper quadrant abdominal tenderness.

Isoniazid therapy may be reinstituted when liver function tests return to baseline and symptoms of toxicity resolve.

Dose Adjustments

The dose should be reduced in severe hepatic disease.

Precautions

US BOXED WARNING:
HEPATITIS:
-Severe and sometimes fatal hepatitis associated with isoniazid therapy may occur and may develop even after many months of treatment.
-The risk of developing hepatitis is increased with daily consumption of alcohol; and in general, the incidence of hepatitis increases with age.
-Serum transaminase concentration becomes elevated in about 10% to 20% of patients, usually during the first few months of therapy but can occur at any time.
-Liver enzyme levels often return to normal despite continuance of isoniazid, but cases of progressive liver dysfunction have occurred.
-Carefully monitor and interview patients at monthly intervals; advise patients to immediately report if they experience any of the prodromal hepatitis symptoms (e.g., fatigue, weakness, malaise, anorexia, nausea, vomiting).
-Promptly discontinue this drug if any signs/symptoms of hepatic damage are detected as this drug has been reported to cause a more severe form of liver damage.
-If this drug is discontinued, patients with tuberculosis should be given appropriate treatment with alternative drugs.
-If this drug must be reinstated, treatment should be resumed only after symptoms and laboratory abnormalities have cleared.
-This drug should be restarted in very small and gradually increasing doses and should be immediately withdrawn if there is any indication of recurrent liver involvement.
-Treatment should be deferred in persons with acute hepatic diseases.

Consult WARNINGS section for additional precautions.

Patients with tuberculosis who have hepatitis attributed to isoniazid should be administered appropriate treatment with alternative drugs. If isoniazid must be reinstated, it should be reinstituted only after symptoms and laboratory abnormalities have resolved. Isoniazid be restarted in very small and gradually increasing doses and should be withdrawn immediately if there is any indication of recurrent liver involvement.

Preventive therapy should be deferred in persons with acute hepatic diseases.

All drugs should be stopped and an evaluation conducted at the first sign of a hypersensitivity reaction. If isoniazid treatment must be reinstituted, it should be given only after symptoms have cleared. Isoniazid should be restarted in very small and gradually increasing doses and should be withdrawn immediately if there is any indication of recurrent hypersensitivity reaction.

Isoniazid should be carefully monitored in patients with the following: severe renal dysfunction, concurrent use of any chronically administered medication, history of previous discontinuation of isoniazid, existence of peripheral neuropathy or conditions predisposing to neuropathy, injection drug use, HIV seropositive patients, pregnancy, and women belonging to a minority group, especially during the postpartum period.

Continuous administration of isoniazid for a sufficient period of time is an essential part of the regimen because relapse rates are higher if chemotherapy is stopped prematurely. In the treatment of tuberculosis, resistant organisms may multiply and their emergence during the treatment may necessitate a change in the regimen.

Dialysis

Isoniazid is dialyzable (50% to 100%) by hemodialysis.

Other Comments

Pyridoxine, 50 mg orally once a day, may be administered with isoniazid to prevent the occurrence of peripheral neuropathy.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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