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ALERT: U.S. Boxed Warning
The FDA-approved labeling includes a boxed warning. See Warnings/Precautions section for a concise summary of this information. For verbatim wording of the boxed warning, consult the product labeling or www.fda.gov.
Pronunciation
(eye soe NYE a zid)
Generic Available (U.S.)
Yes
Index Terms
Canadian Brand Names
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Treatment of susceptible tuberculosis infections; treatment of latent tuberculosis infection (LTBI)
Pregnancy Risk Factor
C
Pregnancy Considerations
Isoniazid was found to be embryocidal in animal studies; teratogenic effects were not noted. Isoniazid crosses the human placenta. Due to the risk of tuberculosis to the fetus, treatment is recommended when the probability of maternal disease is moderate to high. The CDC recommends isoniazid as part of the initial treatment regimen (CDC, 2003). Pyridoxine supplementation is recommended (25 mg/day).
Lactation
Enters breast milk/compatible
Breast-Feeding Considerations
Small amounts of isoniazid are excreted in breast milk. However, women with tuberculosis should not be discouraged from breast-feeding. Pyridoxine supplementation is recommended for the mother and infant.
Contraindications
Hypersensitivity to isoniazid or any component of the formulation; acute liver disease; previous history of hepatic damage during isoniazid therapy; previous severe adverse reaction (drug fever, chills, arthritis) to isoniazid
Warnings/Precautions
Boxed warnings:
• Hepatitis: See “Concerns related to adverse effects” below.
Concerns related to adverse effects:
• Hepatitis: [U.S. Boxed Warning]: Severe and sometimes fatal hepatitis may occur; usually occurs within the first 3 months of treatment, although may develop even after many months of treatment. The risk of developing hepatitis is age-related, although isoniazid-induced hepatotoxicity has been reported in children; daily ethanol consumption may also increase the risk. Patients must report any prodromal symptoms of hepatitis, such as fatigue, weakness, malaise, anorexia, nausea, abdominal pain, jaundice, or vomiting. Patients should be instructed to immediately discontinue therapy if any of these symptoms occur, even if a clinical evaluation has yet to be conducted.
• Peripheral neuropathies: Pyridoxine (10-50 mg/day) is recommended in individuals at risk for development of peripheral neuropathies (eg, HIV infection, nutritional deficiency, diabetes, pregnancy).
Disease-related concerns:
• Hepatic impairment: Use with caution in patients with hepatic impairment. Treatment with isoniazid for latent tuberculosis infection should be deferred in patients with acute hepatic diseases.
• Renal impairment: Use with caution in patients with severe renal impairment.
Other warnings/precautions:
• Appropriate use: Multidrug regimens should be utilized for the treatment of active tuberculosis to prevent the emergence of drug resistance.
• Ophthalmic exams: Periodic ophthalmic examinations are recommended even when usual symptoms do not occur.
Adverse Reactions
Frequency not defined.
Cardiovascular: Hypertension, palpitation, tachycardia, vasculitis
Central nervous system: Depression, dizziness, encephalopathy, fever, lethargy, memory impairment, psychosis, seizure, slurred speech, toxic encephalopathy
Dermatologic: Flushing, rash (morbilliform, maculopapular, pruritic, or exfoliative)
Endocrine & metabolic: Gynecomastia, hyperglycemia, metabolic acidosis, pellagra, pyridoxine deficiency
Gastrointestinal: Anorexia, epigastric distress, nausea, stomach pain, vomiting
Hematologic: Agranulocytosis, anemia (sideroblastic, hemolytic, or aplastic), eosinophilia, thrombocytopenia
Hepatic: LFTs mildly increased (10% to 20%), hyperbilirubinemia, bilirubinuria, jaundice, hepatic dysfunction, hepatitis (may involve progressive liver damage; risk increases with age; 2.3% in patients >50 years)
Neuromuscular & skeletal: Arthralgia, hyper-reflexia, paresthesia, peripheral neuropathy (dose-related incidence, 10% to 20% incidence with 10 mg/kg/day), weakness
Ocular: Blurred vision, loss of vision, optic neuritis and atrophy
Miscellaneous: Lupus-like syndrome, lymphadenopathy, rheumatic syndrome
Metabolism/Transport Effects
Substrate of CYP2E1 (major); Inhibits CYP1A2 (weak), 2A6 (moderate), 2C9 (weak), 2C19 (strong), 2D6 (moderate), 2E1 (moderate), 3A4 (strong); Induces CYP2E1 (after discontinuation) (weak)
Drug Interactions
Acetaminophen: Isoniazid may enhance the adverse/toxic effect of Acetaminophen. Risk C: Monitor therapy
Alfuzosin: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Alfuzosin. Risk X: Avoid combination
Almotriptan: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Almotriptan. Management: Limit initial almotriptan adult dose to 6.25 mg and maximum adult dose to 12.5 mg/24-hrs when used with a strong CYP3A4 inhibitor. Avoid concurrent use in patients with impaired hepatic or renal function. Risk D: Consider therapy modification
Alosetron: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Alosetron. Risk C: Monitor therapy
Antacids: May decrease the absorption of Isoniazid. Risk D: Consider therapy modification
Benzodiazepines (metabolized by oxidation): Isoniazid may decrease the metabolism of Benzodiazepines (metabolized by oxidation). Risk C: Monitor therapy
Bortezomib: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Bortezomib. Risk C: Monitor therapy
Brinzolamide: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Brinzolamide. Risk C: Monitor therapy
Budesonide (Nasal): CYP3A4 Inhibitors (Strong) may increase the serum concentration of Budesonide (Nasal). Risk C: Monitor therapy
Budesonide (Systemic, Oral Inhalation): CYP3A4 Inhibitors (Strong) may increase the serum concentration of Budesonide (Systemic, Oral Inhalation). Management: Consider reducing the oral budesonide dose when used together with a CYP3A4 inhibitor. This interaction is likely less severe with orally inhaled budesonide. Monitor patients closely for signs/symptoms of corticosteroid excess. Risk D: Consider therapy modification
CarBAMazepine: Isoniazid may decrease the metabolism of CarBAMazepine. Risk D: Consider therapy modification
Chlorzoxazone: Isoniazid may decrease the metabolism of Chlorzoxazone. Risk C: Monitor therapy
Ciclesonide: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Ciclesonide. Specifically, concentrations of the active des-ciclesonide metabolite may be increased. Risk C: Monitor therapy
Clopidogrel: CYP2C19 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Clopidogrel. Risk X: Avoid combination
Codeine: CYP2D6 Inhibitors (Moderate) may diminish the therapeutic effect of Codeine. These CYP2D6 inhibitors may prevent the metabolic conversion of codeine to its active metabolite morphine. Risk C: Monitor therapy
Colchicine: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Colchicine. Management: Colchicine is contraindicated in patients with impaired renal or hepatic function who are also receiving a strong CYP3A4 inhibitor. In those with normal renal and hepatic function, reduce colchicine dose as directed. Risk D: Consider therapy modification
Conivaptan: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Conivaptan. Risk X: Avoid combination
Corticosteroids (Orally Inhaled): CYP3A4 Inhibitors (Strong) may increase the serum concentration of Corticosteroids (Orally Inhaled). Management: Monitor for signs and symptoms of adrenal suppression if inhaled budesonide or mometasone are coadministered with a strong CYP3A4 inhibitor. Avoid combining inhaled fluticasone with any strong CYP3A4 inhibitor. Exceptions: Beclomethasone; Beclomethasone (Oral Inhalation); Flunisolide; Flunisolide (Oral Inhalation); Triamcinolone; Triamcinolone (Systemic). Risk C: Monitor therapy
Corticosteroids (Systemic): May decrease the serum concentration of Isoniazid. Risk C: Monitor therapy
CycloSERINE: Isoniazid may enhance the adverse/toxic effect of CycloSERINE. Specifically, CNS toxicity may be enhanced. Risk C: Monitor therapy
CYP2A6 Substrates: CYP2A6 Inhibitors (Moderate) may decrease the metabolism of CYP2A6 Substrates. Risk C: Monitor therapy
CYP2C19 Substrates: CYP2C19 Inhibitors (Strong) may decrease the metabolism of CYP2C19 Substrates. Risk D: Consider therapy modification
CYP2D6 Substrates: CYP2D6 Inhibitors (Moderate) may decrease the metabolism of CYP2D6 Substrates. Exceptions: Tamoxifen. Risk C: Monitor therapy
CYP2E1 Substrates: CYP2E1 Inhibitors (Moderate) may decrease the metabolism of CYP2E1 Substrates. Risk C: Monitor therapy
CYP3A4 Substrates: CYP3A4 Inhibitors (Strong) may decrease the metabolism of CYP3A4 Substrates. Risk D: Consider therapy modification
Dienogest: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Dienogest. Risk C: Monitor therapy
Dronedarone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Dronedarone. Risk X: Avoid combination
Dutasteride: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Dutasteride. Risk C: Monitor therapy
Eplerenone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Eplerenone. Risk X: Avoid combination
Everolimus: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Everolimus. Risk X: Avoid combination
FentaNYL: CYP3A4 Inhibitors (Strong) may increase the serum concentration of FentaNYL. Management: Monitor patients extra closely for several days following initiation of the combination, and fentanyl dosage reductions should be made as appropriate. Risk D: Consider therapy modification
Fesoterodine: CYP3A4 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Fesoterodine. Management: Avoid fesoterodine doses greater than 4 mg daily in adult patients who are also receiving strong CYP3A4 inhibitors. Risk D: Consider therapy modification
Fluticasone (Nasal): CYP3A4 Inhibitors (Strong) may increase the serum concentration of Fluticasone (Nasal). Risk C: Monitor therapy
Fluticasone (Oral Inhalation): CYP3A4 Inhibitors (Strong) may increase the serum concentration of Fluticasone (Oral Inhalation). Risk X: Avoid combination
Fosphenytoin: Isoniazid may increase the serum concentration of Fosphenytoin. Management: Consider alternatives. If concomitant therapy cannot be avoided, monitor for increased phenytoin concentrations/effects with isoniazid initiation/dose increase, or decreased concentrations/effects with isoniazid discontinuation/dose decrease. Risk D: Consider therapy modification
GuanFACINE: CYP3A4 Inhibitors (Strong) may increase the serum concentration of GuanFACINE. Risk C: Monitor therapy
Halofantrine: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Halofantrine. Risk X: Avoid combination
Iloperidone: CYP3A4 Inhibitors (Strong) may increase serum concentrations of the active metabolite(s) of Iloperidone. Specifically, concentrations of the metabolites P88 and P95 may be increased. CYP3A4 Inhibitors (Strong) may increase the serum concentration of Iloperidone. Management: Reduce iloperidone dose by half when administered with a strong CYP3A4 inhibitor. Risk D: Consider therapy modification
Ixabepilone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Ixabepilone. Risk D: Consider therapy modification
Lumefantrine: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Lumefantrine. Risk C: Monitor therapy
Lurasidone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Lurasidone. Risk X: Avoid combination
Maraviroc: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Maraviroc. Management: Reduce the adult dose of maraviroc to 150 mg twice daily when used with a strong CYP3A4 inhibitor. Do not use maraviroc with strong CYP3A4 inhibitors in patients with Clcr less than 30 mL/min. Risk D: Consider therapy modification
MethylPREDNISolone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of MethylPREDNISolone. Management: Consider methylprednisolone dose titration and/or adjustments in patients receiving strong CYP3A4 inhibitors (eg, azole antifungals, protease inhibitors) and monitor for increased steroid related adverse effects. Risk D: Consider therapy modification
Nebivolol: CYP2D6 Inhibitors (Moderate) may increase the serum concentration of Nebivolol. Risk C: Monitor therapy
Nilotinib: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Nilotinib. Risk X: Avoid combination
Nisoldipine: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Nisoldipine. Risk X: Avoid combination
Paricalcitol: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Paricalcitol. Risk C: Monitor therapy
Pazopanib: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Pazopanib. Management: Avoid concurrent use of pazopanib with strong inhibitors of CYP3A4 whenever possible. If it is not possible to avoid such a combination, reduce pazopanib adult dose to 400 mg. Further dose reductions may also be required. Risk D: Consider therapy modification
Phenytoin: Isoniazid may increase the serum concentration of Phenytoin. Management: Consider alternatives. If concomitant therapy cannot be avoided, monitor for increased phenytoin concentrations/effects with isoniazid initiation/dose increase, or decreased concentrations/effects with isoniazid discontinuation/dose decrease. Risk D: Consider therapy modification
Pimecrolimus: CYP3A4 Inhibitors (Strong) may decrease the metabolism of Pimecrolimus. Risk C: Monitor therapy
Prasugrel: CYP3A4 Inhibitors (Strong) may decrease serum concentrations of the active metabolite(s) of Prasugrel. Risk C: Monitor therapy
Ranolazine: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Ranolazine. Risk X: Avoid combination
Rifamycin Derivatives: May enhance the hepatotoxic effect of Isoniazid. Even so, this is a frequently employed combination regimen. Risk C: Monitor therapy
Rivaroxaban: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Rivaroxaban. Risk X: Avoid combination
RomiDEPsin: CYP3A4 Inhibitors (Strong) may increase the serum concentration of RomiDEPsin. Risk X: Avoid combination
Salmeterol: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Salmeterol. Risk X: Avoid combination
Saxagliptin: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Saxagliptin. Management: Limit saxagliptin adult dose to 2.5 mg/day and monitor for increased saxagliptin levels/effects (e.g., hypoglycemia) when used with a strong CYP3A4 inhibitor. Monitor for decreased saxagliptin levels/effects if discontinuing CYP3A4 inhibitor. Risk D: Consider therapy modification
Silodosin: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Silodosin. Risk X: Avoid combination
SORAfenib: CYP3A4 Inhibitors (Strong) may increase the serum concentration of SORAfenib. Risk C: Monitor therapy
Tadalafil: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Tadalafil. Management: Erectile dysfunction: tadalafil max = 2.5 mg/day (daily use) or 10 mg/72 hrs (as needed use) (adult doses). Avoid use of tadalafil with a strong CYP3A4 inhibitor for treatment of pulmonary arterial hypertension. Risk D: Consider therapy modification
Tamoxifen: CYP2D6 Inhibitors (Moderate) may decrease the metabolism of Tamoxifen. Specifically, CYP2D6 inhibitors may decrease the formation of highly potent active metabolites. Management: Consider alternatives with less of an inhibitory effect on CYP2D6 activity when possible. Risk D: Consider therapy modification
Tamsulosin: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Tamsulosin. Risk X: Avoid combination
Theophylline Derivatives: Isoniazid may increase the serum concentration of Theophylline Derivatives. Exceptions: Dyphylline. Risk C: Monitor therapy
Thioridazine: CYP2D6 Inhibitors may decrease the metabolism of Thioridazine. Risk X: Avoid combination
Tolvaptan: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Tolvaptan. Risk X: Avoid combination
Toremifene: CYP3A4 Inhibitors (Strong) may enhance the adverse/toxic effect of Toremifene. CYP3A4 Inhibitors (Strong) may increase the serum concentration of Toremifene. Risk X: Avoid combination
TraMADol: CYP2D6 Inhibitors (Moderate) may diminish the therapeutic effect of TraMADol. These CYP2D6 inhibitors may prevent the metabolic conversion of tramadol to its active metabolite that accounts for much of its opioid-like effects. Risk C: Monitor therapy
Vilazodone: CYP3A4 Inhibitors (Strong) may increase the serum concentration of Vilazodone. Management: Limit maximum adult vilazodone dose to 20 mg/day in patients receiving strong CYP3A4 inhibitors. Risk D: Consider therapy modification
Ethanol/Nutrition/Herb Interactions
Ethanol: Avoid ethanol (increases the risk of hepatitis).
Food: Isoniazid should not be taken with food; serum levels may be decreased if taken with food. Has some ability to inhibit tyramine metabolism; several case reports of mild reactions (flushing, palpitations) after ingestion of cheese (with or without wine). Reactions resembling allergic symptoms following ingestion of fish high in histamine content have been reported. Isoniazid decreases folic acid absorption. Isoniazid alters pyridoxine metabolism.
Storage
Tablet: Store at 20°C to 25°C (68°F to 77°F). Protect from light.
Oral solution: Store at 15°C to 30°C (59°F to 86°F). Protect from light.
Mechanism of Action
Unknown, but may include the inhibition of mycolic acid synthesis resulting in disruption of the bacterial cell wall
Pharmacodynamics/Kinetics
Absorption: Rapid and complete; rate can be slowed with food
Distribution: All body tissues and fluids including CSF; crosses placenta; enters breast milk
Protein binding: 10% to 15%
Metabolism: Hepatic with decay rate determined genetically by acetylation phenotype
Half-life elimination: Fast acetylators: 30-100 minutes; Slow acetylators: 2-5 hours; may be prolonged with hepatic or severe renal impairment
Time to peak, serum: 1-2 hours
Excretion: Urine (75% to 95%); feces; saliva
Dosage
Usual dosage ranges: Oral, I.M.:
Infants and Children: 10-15 mg/kg/day once daily (maximum: 300 mg/day) or 20-40 mg/kg given 2-3 times per week (maximum: 900 mg/dose)
Adults: 5 mg/kg/day (usual: 300 mg/day) as a single daily dose or 15 mg/kg (maximum: 900 mg/dose) given 2-3 times per week
Indication-specific dosing: Oral, I.M.: Recommendations often change due to resistant strains and newly-developed information; consult MMWR for current CDC recommendations. Intramuscular injection is available for patients who are unable to either take or absorb oral therapy.
Infants and Children:
Tuberculosis, active:
Daily therapy: CDC recommendations: 10-15 mg/kg/day once daily (maximum: 300 mg/day) (MMWR, 2003)
Directly observed therapy (DOT): CDC recommendations: 20-30 mg/kg (maximum: 900 mg/dose) twice weekly (MMWR, 2003); Manufacturer's labeling: 20-40 mg/kg (maximum: 900 mg/dose) twice weekly or 3 times/week
Tuberculosis, latent infection (LTBI):
Daily therapy: CDC recommendations: 10-20 mg/kg/day once daily (maximum: 300 mg/dose) (MMWR, 2000); Manufacturer's labeling: 10 mg/kg/day once daily (maximum: 300 mg/dose)
Directly observed therapy (DOT): CDC recommendations: 20-40 mg/kg (maximum: 900 mg/dose) twice weekly for 9 months (MMWR, 2000); Manufacturer's labeling: 20-30 mg/kg twice weekly (maximum: 900 mg/dose)
Adults: Note: Concomitant administration of 10-50 mg/day pyridoxine is recommended in malnourished patients or those prone to neuropathy (eg, alcoholics, patients with diabetes).
Nontuberculous mycobacterium
(M. kansasii)
(unlabeled use): 5 mg/kg/day (maximum: 300 mg/day) for duration to include 12 months of culture-negative sputum; typically used in combination with ethambutol and rifampin
Tuberculosis, active:
Daily therapy: CDC recommendations: 5 mg/kg/day once daily (usual dose: 300 mg/day) (MMWR, 2003)
Directly observed therapy (DOT): CDC recommendations: 15 mg/kg (maximum: 900 mg/dose) twice weekly or 3 times/week; Note: CDC guidelines state that once-weekly therapy (15 mg/kg/dose) may be considered, but only after the first 2 months of initial therapy in HIV-negative patients, and only in combination with rifapentine. (MMWR, 2003)
Note: Treatment may be defined by the number of doses administered (eg, “six-month” therapy involves 182 doses of INH and rifampin, and 56 doses of pyrazinamide). Six months is the shortest interval of time over which these doses may be administered, assuming no interruption of therapy.
Tuberculosis, latent infection (LTBI): CDC recommendations: 5 mg/kg (maximum: 300 mg/dose) once daily or 15 mg/kg (maximum: 900 mg/dose) twice weekly by directly observed therapy (DOT) 6-9 months in patients who do not have HIV infection (9 months is optimal, 6 months may be considered to reduce costs of therapy) and 9 months in patients who have HIV infection. Extend to 12 months of therapy if interruptions in treatment occur. (MMWR, 2000)
Dosing adjustment in renal impairment: No adjustment necessary
Hemodialysis: Dialyzable (50% to 100%); administer dose post dialysis
Dosing adjustment in hepatic impairment: No adjustment required, however, use with caution; may accumulate and additional liver damage may occur in patients with pre-existing liver disease. For ALT or AST >3 times the ULN: discontinue or temporarily withhold treatment. Treatment with isoniazid for latent tuberculosis infection should be deferred in patients with acute hepatic diseases.
Administration: Oral
Should be administered 1 hour before or 2 hours after meals on an empty stomach.
Monitoring Parameters
Baseline and periodic (more frequently in patients with higher risk for hepatitis) liver function tests (ALT and AST); sputum cultures monthly (until 2 consecutive negative cultures reported); monitoring for prodromal signs of hepatitis
LTBI therapy: American Thoracic Society/Centers for Disease Control (ATS/CDC) recommendations: Monthly clinical evaluation, including brief physical exam for adverse events. Baseline serum AST or ALT and bilirubin should be considered for patients at higher risk for adverse events (eg, history of liver disease, chronic ethanol use, HIV-infected patients, women who are pregnant or postpartum ≤3 months, older adults with concomitant medications or diseases). Routine, periodic monitoring is recommended for any patient with an abnormal baseline or at increased risk for hepatotoxicity.
Test Interactions
False-positive urinary glucose with Clinitest®
Dietary Considerations
Should be taken 1 hour before or 2 hours after meals on an empty stomach; increase dietary intake of folate, niacin, magnesium. Avoid tyramine-containing foods; some examples include aged or matured cheese, air-dried or cured meats (including sausages and salamis), fava or broad bean pods, tap/draft beers, Marmite concentrate, sauerkraut, soy sauce and other soybean condiments. Avoid histamine-containing foods.
Patient Education
Best if taken on an empty stomach, 1 hour before or 2 hours after meals. Avoid excessive alcohol and tyramine-containing foods. Increase dietary intake of folate, niacin, and magnesium. You will need to have frequent ophthalmic exams and periodic medical check-ups to evaluate drug effects. If you experience nausea, vomiting, loss of appetite, weakness, fatigue, abdominal pain, dark-colored urine or change in color of stool, or yellowing of eyes/skin, discontinue and contact prescriber as soon as possible. Report chest pain, rapid heart beat, or palpitations; tingling, numbness, or loss of sensation in hands or feet; CNS changes (depression, dizziness, memory impairment, slurred speech, seizure); unusual weakness or fatigue; persistent gastrointestinal upset; change in vision; or skin rash.
Geriatric Considerations
Age has not been shown to affect the pharmacokinetics of INH since acetylation phenotype determines clearance and half-life, acetylation rate does not change significantly with age. Most strains of M. tuberculosis found the elderly should be susceptible to INH since most acquired their initial infection prior to INH's introduction.
Additional Information
The AAP recommends that pyridoxine supplementation (1-2 mg/kg/day) should be administered to malnourished patients, children or adolescents on meat or milk-deficient diets, breast-feeding infants, and those predisposed to neuritis to prevent peripheral neuropathy; administration of isoniazid syrup has been associated with diarrhea
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia (normal salivary flow resumes upon discontinuation).
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Effects on Mental Status
May cause drowsiness or dizziness; may rarely cause depression or psychosis; reports of insomnia, restlessness, disorientation, hallucinations, delusions, obsessive-compulsive symptoms, and exacerbation of schizophrenia
Mental Health: Effects on Psychiatric Treatment
Isoniazid may impair the metabolism of carbamazepine and oxidatively metabolized benzodiazepines; monitor for adverse effects
Nursing: Physical Assessment/Monitoring
Use caution with pre-existing renal impairment or hepatic disease. Monitor for liver damage, nausea, vomiting, peripheral neuropathy, and CNS changes at regular intervals during therapy. Teach patient importance of proper diet and ophthalmic examinations.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Injection, solution: 100 mg/mL (10 mL)
Solution, oral: 50 mg/5 mL (473 mL)
Tablet, oral: 100 mg, 300 mg
Pricing: U.S. (www.drugstore.com)
Syrup (Isoniazid)
50 mg/5 mL (473): $77.14
Tablets (Isoniazid)
100 mg (30): $13.99
300 mg (90): $17.00
Extemporaneously Prepared
Note: Commercial oral solution is available (50 mg/mL)
A 10 mg/mL oral suspension may be made with tablets, purified water, and sorbitol. Crush ten 100 mg tablets in a mortar and reduce to a fine powder. Add 10 mL of purified water and mix to a uniform paste. Mix while adding sorbitol in incremental proportions to almost 100 mL; transfer to a graduated cylinder, rinse mortar with sorbitol, and add quantity of sorbitol sufficient to make 100 mL (do not use sugar-based solutions). Label "shake well" and "refrigerate". Stable for 21 days refrigerated.
Nahata MC, Pai VB, and Hipple TF, Pediatric Drug Formulations, 5th ed, Cincinnati, OH: Harvey Whitney Books Co, 2004.
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International Brand Names
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Last full review/revision May 2011
Content last modified May 2011
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