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an antibacterial compound used in treatment of tuberculosis.

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.


Abbreviation for isonicotinic acid hydrazide.


A trademark for the drug isoniazid.


abbreviation for isonicotinic acid hydrazide. See isoniazid.


Isoniazid, see there.


Abbreviation for isoniazid.
References in periodicals archive ?
In 236 non-treated candidates, 4 were Sensitive to INH and RIF while the remaining 4 were MDR-TB.
While functional anti-FceRIa or anti-lgE can cause histamine release and risk of anaphylaxis, C1 INH deficiency or dysfunction and increased bradykinin can lead to risk of laryngeal angioedema, and things as simple as a tooth extraction can be life-threatening, as well as the endotracheal intubation meant to save a life, "Trauma, including surgically induced trauma, especially involving endotracheal intubation or manipulation, may trigger life-threatening laryngeal edema.
In the GenoType MTBDR plus assay, INH resistance was detected using probes of the katG and inhA genes.
To conclude, direct NRA is simple, easy to perform, rapid, relatively less expensive, without requirement of expensive reagents and sophisticated equipments useful tool suitable for early determination, first line anti-tubercular drugs namely rifampicin, isoniazid, ethambutol, and streptomycin with excellent concordance for INH and RIF resistance and relatively low accuracy for streptomycin, with good sensitivity and specificity with overall accuracy of NRA was 95.
This has only been described in one other INH toxicity case report, where INH was combined with rifampicin.
Abbreviations: (-)-DPG, (-)-deoxypergularinine; TB, tuberculosis; MDR-TB, multidrug-resistant tuberculosis; XDR-TB, extensively drug-resistant tuberculosis; MGIT, mycobacteria growth indicator tube; MICs, minimum inhibitory concentrations; INH, isoniazid; TMV, tobacco mosaic virus; MIC, minimum inhibitory concentration; FICIs, fractional inhibitory concentration indices.
Discriminant analyses were performed to build predictive models of INH and RIF resistance based on genotyping data of the four genetic markers used, alone or in combination.
Memorial Sloan-Kettering implemented weekly rifapentine plus INH for its LTBI personnel in 2011.
Peripheral neuropathy is a less common adverse effect of INH.
Therefore, this study was aimed at determining the patterns of mutations in rpoB gene (for detecting RIF resistance) and katG and inhA genes (for detecting INH resistance) in Mycobacterium tuberculosis strains isolated from Nepalese patients and evaluating the performance of Genotype MTBDRplus against conventional DST.
Also, it is not clear what approach should be followed when the healthcare worker fails to re-introduce some of the first-line drugs, especially INH or RIF.