INH

INH (nch)

abbr.

isoniazid

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INH,

abbreviation for isonicotinic acid hydrazide. See isoniazid.

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isoniazid (INH)

Isotamine (CA), PMS Isoniazid (CA)

Pharmacologic class: Isonicotinic acid hydrazide

Therapeutic class: Antitubercular

Pregnancy risk category C

FDA Boxed 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. Isoniazid-associated 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 isoniazid-associated 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.

Action

Inhibits cell-wall biosynthesis by interfering with lipid and nucleic acid DNA synthesis in tubercle bacilli cells

Availability

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

Off-label uses

• Mycobacterium kansasii infection

Contraindications

• Hypersensitivity to drug
• Acute hepatic disease or previous hepatitis caused by isoniazid therapy

Precautions

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.

Administration

• 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.

Route	Onset	Peak	Duration
P.O., I.M.	Rapid	1-2 hr	Up to 24 hr

Adverse reactions

CNS: peripheral neuropathy, dizziness, memory impairment, slurred speech, psychosis, toxic encephalopathy, seizures

EENT: visual disturbances

GI: nausea, vomiting

GU: gynecomastia

Hematologic: eosinophilia, methemoglobinemia, hemolytic anemia, aplastic anemia, agranulocytosis, thrombocytopenia

Hepatic: hepatitis

Metabolic: pyridoxine deficiency, hyperglycemia, metabolic acidosis

Respiratory: dyspnea

Other: fever, pellagra, lupuslike syndrome, injection site irritation, hypersensitivity reaction

Interactions

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

Patient monitoring

• Assess hepatic enzyme levels.
• Watch for adverse reactions, such as peripheral neuropathy.

Patient teaching

• 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.

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INH

Isoniazid, see there