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Pharmacologic class: Isonicotinic acid hydrazide
Therapeutic class: Antitubercular
Pregnancy risk category C
FDA Box Warning
• Severe and sometimes fatal hepatitis has occurred, even after many months of treatment. Risk increases with age until 64, then decreases after age 65. Risk also rises with daily alcohol consumption. Monitor patients carefully and interview them monthly. For persons aged 35 and older, also measure liver enzymes before therapy starts and periodically throughout. Isoniazidassociated hepatitis usually arises during first 3 months of therapy. Hepatitis risk also increases with daily alcohol use, chronic hepatic disease, and injection drug use. Recent report suggests increased risk of fatal hepatitis among women; risk also may increase during postpartum period. If adverse effects or signs and symptoms of hepatic damage occur, discontinue drug promptly.
• Tuberculosis patients with Isoniazidassociated hepatitis should receive appropriate treatment with alternative drugs. If isoniazid must be restarted, do so only after symptoms and laboratory abnormalities resolve. Restart in small and gradually increasing doses, and withdraw drug immediately at any indication of recurrent liver involvement. Defer preventive treatment in patients with acute hepatic disease.
Inhibits cell-wall biosynthesis by interfering with lipid and nucleic acid DNA synthesis in tubercle bacilli cells
Injection: 100 mg/ml
Syrup: 50 mg/5 ml
Tablets: 100 mg, 300 mg
Indications and dosages
➣ Active tuberculosis (TB)
Adults: 5 mg/kg P.O. or I.M. (maximum of 300 mg/day) daily as a single dose, or 15 mg/kg (maximum of 900 mg/day) two to three times weekly; given with other agents
Children: 10 to 15 mg/kg P.O. or I.M. (maximum of 300 mg/day) daily as a single dose, or 20 to 40 mg/kg (maximum of 900 mg/day) two to three times weekly
➣ To prevent TB in patients exposed to active disease
Adults: 300 mg P.O. daily as a single dose for 6 to 12 months
Children and infants: 10 mg/kg P.O. daily as a single dose for up to 12 months
• Mycobacterium kansasii infection
• Hypersensitivity to drug
• Acute hepatic disease or previous hepatitis caused by isoniazid therapy
Use cautiously in:
• severe renal impairment, diabetes, diabetic retinopathy, ocular defects, chronic alcoholism, hepatic damage
• Black or Hispanic women
• pregnant or breastfeeding patients
• children ages 13 and younger.
• Give on empty stomach 1 hour before or 2 hours after meals. If GI upset occurs, administer with food.
• Administer parenterally only if patient can't receive oral form.
• Use cautiously in diabetic or alcoholic patients and those at risk for neuropathy.
CNS: peripheral neuropathy, dizziness, memory impairment, slurred speech, psychosis, toxic encephalopathy, seizures
EENT: visual disturbances
GI: nausea, vomiting
Hematologic: eosinophilia, methemoglobinemia, hemolytic anemia, aplastic anemia, agranulocytosis, thrombocytopenia
Metabolic: pyridoxine deficiency, hyperglycemia, metabolic acidosis
Other: fever, pellagra, lupuslike syndrome, injection site irritation, hypersensitivity reaction
Drug-drug. Aluminum-containing antacids: decreased isoniazid absorption
Bacille Calmette-Guérin vaccine: ineffective vaccination
Carbamazepine: increased carbamazepine blood level
Disulfiram: psychotic reactions, incoordination
Hepatotoxic drugs: increased risk of hepatotoxicity
Ketoconazole: decreased ketoconazole blood level and efficacy
Other antituberculars: additive CNS toxicity
Phenytoin: inhibition of phenytoin metabolism
Drug-diagnostic tests. Albumin: increased level
Drug-food. Foods containing tyramine: hypertensive crisis, other severe reactions
Drug-behaviors. Alcohol use: increased risk of hepatitis
• Assess hepatic enzyme levels.
• Watch for adverse reactions, such as peripheral neuropathy.
• Advise patient to take once daily on empty stomach, 1 hour before or 2 hours after meals. If GI upset occurs, tell him to take with small amount of food.
• Caution patient to avoid foods containing tyramine (such as cheese, fish, salami, red wine, and yeast extracts), because drug-food interaction may cause chills, diaphoresis, and palpitations.
• Teach patient with peripheral neuropathy to take care to prevent burns and other injuries.
• Instruct patient to report anorexia, nausea, vomiting, jaundice, dark urine, and numbness or tingling of hands or feet.
• Tell patient he'll need periodic medical and eye examinations and blood tests to gauge drug effects.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs, tests, foods, and behaviors mentioned above.