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an antibacterial compound used in treatment of tuberculosis.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

isoniazid (INH)

Dom-Isoniazid (CA), Isotamine (CA), PMS Isoniazid (CA), Rifater (UK), Rifinah (UK), Rimactazid (UK)

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

Off-label uses

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.

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


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.

McGraw-Hill Nurse's Drug Handbook, 7th Ed. Copyright © 2013 by The McGraw-Hill Companies, Inc. All rights reserved


Abbreviation for isonicotinic acid hydrazide.
Farlex Partner Medical Dictionary © Farlex 2012


A trademark for the drug isoniazid.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Isoniazid, see there.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.


Abbreviation for isoniazid.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
The aim of this study was to retrospectively determine the prevalence of katG, inhA and katG plus inhA genetic mutations associated with INH resistance in patients from the FS with MDR-TB identified by LPA during 2014-2016.
The 1H NMR spectra of INH and its metal complexes were recorded in DMSO-d6 on an Avance AV-400 and 500 MHz spectrometer.
INH intoxication causes drug-resistant convulsions by decreasing GABA levels in central nervous system which leads to lower seizure threshold.
Biochemical maternal serum markers in second trimester (15th to 18th week of gestation) were obtained from 155 pregnant women with single pregnancy for hCG, AFP, Inh A and uE3.
Among 106 INH resistant isolates, 97(91%) were associated with katG mutation while 24 (22%) with promoter region of inhA.
Cells of MTB untreated (control) and INH treated at exponential phase were used for whole cell lipid extraction by modified Folch method [21,23].
(9,45,46) In a CFS cohort with decreased C1 INH and complement C4, there was an increased frequency of autoantibodies, especially anti-thyroid microsomal and ANA; circulating immune complexes (42%); and, "...
LJ medium impregnated one antituberculosis drug was used for DST and the critical drug concentrations were 0.2 [micro]g/ml for INH, 40 [micro]g/ml for RFP, 2 [micro]g/ml for EMB, 30 [micro]g/ml for kanamycin (KM), and 2 [micro]g/ml for ofloxacin (OFX).
Purkan (2011) have identified a katG gene of INH resistant M tuberculosis clinical isolates (L19).
Treatment of TBM consists of an intensive phase with 4 anti-TB drugs for 2 months (typically INH 800 mg/d, rifampin 450 mg/d, pyrazinamide 1000 mg/d, and ethambutol 800 mg/d) and a continuation phase with 2 drugs (INH and rifampin) for 7 to 10 additional months, resulting in a total treatment duration of 9 to 12 months.