Isoniazid Dosage

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Usual Adult Dose for:

Usual Pediatric Dose for:

Additional dosage information:

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

Severe and sometimes fatal hepatitis associated with isoniazid therapy may occur or develop after months of treatment. There were 8 deaths among 174 cases of hepatitis reported among 13,838 persons taking isoniazid. The risk is age related with a greater occurrence reported in patients who are 35 years or older. The risk of hepatitis is also increased in patients who consume alcohol daily, in women, and in minorities. Monthly monitoring and interviewing of patients should take place. Baseline laboratory values should be obtained in patients over 35 years of age and in patients with a history of liver illness or heavy alcohol consumption. Elevated liver function tests per se are not a contraindication to the use of isoniazid unless they indicate worsening or acute liver disease. Strict monitoring of these patients, however, is crucial. If liver function tests exceed 3 to 5 times the upper limit of baseline, isoniazid therapy should be discontinued and liver function tests should be monitored until baseline is achieved. Isoniazid therapy may be reinstituted when liver function tests return to baseline and symptoms of toxicity resolve. 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. Patients should be fully informed regarding the risk of hepatotoxicity associated with isoniazid, educated about the signs and symptoms of liver damage, and instructed to contact their physician immediately if they develop signs or symptoms.

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.

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