Isoniazid

Isoniazid inhibits the synthesis of mycoloic acids, an essential component of the bacterial cell wall. At therapeutic levels isoniazid is bactericidal against actively growing intracellular and extracellular Mycobacterium tuberculosis organisms.

• Isoniazid tablets, USP are recommended for all forms of tuberculosis in which organisms are susceptible. However, active tuberculosis must be treated with multiple concomitant anti-tuberculosis medications to prevent the emergence of drug resistance.ICD-10: A15.9

• Isoniazid is contraindicated in patients who develop severe hypersensitivity reactions, including drug-induced hepatitis; previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid such as drug fever, chills, arthritis; and acute liver disease of any etiology.contraindicated

(See also INDICATIONS AND USAGE ) NOTE For preventive therapy of tuberculous infection and treatment of tuberculosis, it is recommended that physicians be familiar with the following publications: (1) the recommendations of the Advisory Council for the Elimination of Tuberculosis, published in the MMWR: vol 42; RR-4, 1993 and (2) Treatment of Tuberculosis and Tuberculosis Infection in Adults and Children, American Journal of Respiratory and Critical Care Medicine: vol 149; 1359-1374, 1994. For Treatment of Tuberculosis Isoniazid is used in conjunction with other effective anti-tuberculous agents. Drug susceptibility testing should be performed on the organisms initially isolated from all patients with newly diagnosed tuberculosis. If the bacilli becomes resistant, therapy must be changed to agents to which the bacilli are susceptible. Usual Oral Dosage (depending on the regimen used): Adults 5 mg/kg up to 300 mg daily in a single dose; or 15 mg/kg up to 900 mg/day, two or three times/week Children 10 mg/kg to 15 mg/kg up to 300 mg daily in a single dose; or 20 mg/kg to 40 mg/kg up to 900 mg/day, two or three times/week Patients with Pulmonary Tuberculosis Without HIV Infection There are 3 regimen options for the initial treatment of tuberculosis in children and adults: Option 1 Daily isoniazid, rifampin and pyrazinamide for 8 weeks followed by 16 weeks of isoniazid and rifampin daily or 2 to 3 times weekly. Ethambutol or streptomycin should be added to the initial regimen until sensitivity to isoniazid and rifampin is demonstrated.

See the boxed warning . Severe Cutaneous Adverse Reactions Severe cutaneous adverse reactions (SCARs) including toxic epidermal necrolysis (TEN), Stevens-Johnson syndrome (SJS), drug reaction with eosinophilia and systemic symptoms (DRESS), and acute generalized exanthematous pustulosis (AGEP) have been reported with the use of isoniazid (see ADVERSE REACTIONS ). Symptoms can be serious and potentially life threatening. If symptoms or signs of SCARs develop, discontinue isoniazid tablets immediately and institute appropriate therapy. Cerebellar Syndrome Cerebellar syndrome which may include abnormal motor coordination presenting as gait, trunk, and limb ataxia, dysmetria and dysdiadochokinesia, intention tremor, dysarthria, or nystagmus, has been reported in postmarketing case reports with the use of isoniazid (see ADVERSE REACTIONS ). Most cases of cerebellar syndrome involved patients with chronic kidney disease (CKD), however, cerebellar syndrome was also reported in patients without CKD. Discontinue isoniazid tablets if symptoms or signs of cerebellar syndrome occur.

The most frequent reactions are those affecting the nervous system and the liver. Nervous System Reactions Peripheral neuropathy is the most common toxic effect. It is dose-related, occurs most often in the malnourished and in those predisposed to neuritis (e.g., alcoholics and diabetics) and is usually preceded by paresthesias of the feet and hands. The incidence is higher in "slow inactivators". Other neurotoxic effects, which are uncommon with conventional doses, are convulsions, toxic encephalopathy, optic neuritis and atrophy, memory impairment and toxic psychosis. Cerebellar syndrome, which may include abnormal motor coordination manifesting as gait, trunk, and limb ataxia, dysmetria and dysdiadochokinesia, intention tremor, dysarthria, or nystagmus, have been reported in post marketing case reports (see WARNINGS ). Hepatic Reactions See boxed warning . Elevated serum transaminase (SGOT; SGPT), bilirubinemia, bilirubinuria, jaundice and occasionally severe and sometimes fatal hepatitis. The common prodromal symptoms of hepatitis are anorexia, nausea, vomiting, fatigue, malaise and weakness. Mild hepatic dysfunction, evidenced by mild and transient elevation of serum transaminase levels occurs in 10 to 20 percent of patients taking isoniazid. This abnormality usually appears in the first 1 to 3 months of treatment but can occur at any time during therapy. In most instances, enzyme levels return to normal and generally, there is no necessity to discontinue medication during the period of mild serum transaminase elevation.

Pregnancy Teratogenic Effects Pregnancy Category C Isoniazid has been shown to have an embryocidal effect in rats and rabbits when given orally during pregnancy. Isoniazid was not teratogenic in reproduction studies in mice, rats and rabbits. There are no adequate and well-controlled studies in pregnant women. Isoniazid should be used as a treatment for active tuberculosis during pregnancy because the benefit justifies the potential risk to the fetus. The benefit of preventive therapy also should be weighed against a possible risk to the fetus. Preventive therapy generally should be started after delivery to prevent putting the fetus at risk of exposure; the low levels of isoniazid in breast milk do not threaten the neonate. Since isoniazid is known to cross the placental barrier, neonates of isoniazid treated mothers should be carefully observed for any evidence of adverse effects. Nonteratogenic Effects Since isoniazid is known to cross the placental barrier, neonates of isoniazid-treated mothers should be carefully observed for any evidence of adverse effects.

Signs and Symptoms Isoniazid overdosage produces signs and symptoms within 30 minutes to 3 hours after ingestion. Nausea, vomiting, dizziness, slurring of speech, blurring of vision and visual hallucinations (including bright colors and strange designs) are among the early manifestations. With marked overdosage, respiratory distress and CNS depression, progressing rapidly from stupor to profound coma, are to be expected, along with severe, intractable seizures. Severe metabolic acidosis, acetonuria and hyperglycemia are typical laboratory findings. Treatment Untreated or inadequately treated cases of gross isoniazid overdosage, 80 mg/kg to 150 mg/kg, can cause neurotoxicity6 and terminate fatally, but good response has been reported in most patients brought under adequate treatment within the first few hours after drug ingestion. For the Asymptomatic Patient Absorption of drugs from the GI tract may be decreased by giving activated charcoal. Gastric emptying should also be employed in the asymptomatic patient. Safeguard the patient's airway when employing these procedures.

• Aug 24, 1972ANDAANDA080937Genus
• Aug 24, 1972ANDAANDA080936Genus
• Nov 10, 1983ANDAANDA088235Cmp Pharma Inc
• Jun 13, 1988ANDAANDA089776Chartwell Molecular
• Jun 26, 1997ANDAANDA040090Omnivium Pharms
• Jul 21, 1997ANDAANDA081118Chartwell Rx
• Jul 5, 2005ANDAANDA040648Sandoz

Reference statistics from the openFDA drug-shortage dataset. For a live view, consult the FDA database directly. Not clinical guidance.

• Isoniazid, Tablet, 300 mg (NDC 64950-217-03)To be discontinued
  Sponsor: Genus Lifesciences
  Updated Jul 1, 2025
• Isoniazid, Tablet, 300 mg (NDC 64950-217-10)To be discontinued
  Sponsor: Genus Lifesciences
  Updated Jul 1, 2025

1. 1Drug Ineffective1,1667.3%
2. 2Pyrexia1,0976.9%
3. 3Drug Interaction9195.8%
4. 4Nausea8975.6%
5. 5Drug-induced Liver Injury8505.3%
6. 6Off Label Use8325.2%
7. 7Drug Reaction With Eosinophilia And Systemic Symptoms7334.6%
8. 8Vomiting6314.0%
9. 9Headache6133.9%
10. 10Paradoxical Drug Reaction5503.5%
11. 11Arthralgia5443.4%
12. 12Tuberculosis5403.4%
13. 13Diarrhoea5033.2%
14. 14Rash5013.2%
15. 15Condition Aggravated4973.1%

Recent PubMed references pinned to Isoniazid as a MeSH major topic. Citations link to pubmed.ncbi.nlm.nih.gov.

• A Novel Therapy With a One-Month Ultrashort Regimen to Halt Progression From Latent Infection to Active Tuberculosis Among Close Contacts (The TB‑YOUTH Study): Protocol for a Cluster Randomized Controlled Trial.
  JMIR research protocols · 2026 · Yang Y, Zhou F, Ren Y, et al.
  PMID 42247627DOI 10.2196/89584
• Acetylation Variability in Elderly Tunisians: Implications for Isoniazid Dose Individualization.
  Journal of clinical pharmacology · 2026 · Khefacha Y, Ben-Hammamia S, Ben Sassi M, et al.
  PMID 42223414DOI 10.1002/jcph.70217
• Development of Isoniazid-Pyrazole Hybrids as Potential Antitubercular Agents.
  International journal of molecular sciences · 2026 · Kadima MG, Singh V, Kumar G, et al.
  PMID 42196363DOI 10.3390/ijms27104385
• Rapid Eukaryotic Impedimetric Biosensing of Naproxen and Isoniazid: A Proof-of-Concept for Acute Toxicity Monitoring.
  Biosensors · 2026 · Štukovnik Z, Perko N, Bren U, et al.
  PMID 42187494DOI 10.3390/bios16050298
• Protective effect of cornel iridoid glycoside against isoniazid- and rifampicin- induced liver injury via regulating JAK/STAT pathway.
  The Journal of pharmacy and pharmacology · 2026 · Liu J, Han X, Li Y, et al.
  PMID 42160717DOI 10.1093/jpp/rgag047
• Acceptance, completion, and safety of the 3HR regimen for latent tuberculosis infection: a prospective cohort study in China.
  Frontiers in public health · 2026 · Sun Q, Zhang K, Chen J, et al.
  PMID 42088243DOI 10.3389/fpubh.2026.1794409
• Association of katG, inhA, and AhpC Mutations with Isoniazid Resistance of Mycobacterium tuberculosis in Pulmonary Tuberculosis Patients from Nanjing, China.
  Microbial drug resistance (Larchmont, N.Y.) · 2026 · Yang Y, Liu Y, Huang Y, et al.
  PMID 42037600DOI 10.1177/10766294261446052
• Burden and trend of drug resistant tuberculosis: Is the onus on isoniazid monoresistant TB now?
  The Indian journal of tuberculosis · 2026 · Sethi V, Kotwal A, Jethani V, et al.
  PMID 42031455DOI 10.1016/j.ijtb.2025.06.015

The 10 most recently updated of 335 ClinicalTrials.gov registrations naming Isoniazid as an intervention. Registration is not evidence of efficacy or safety — reference crosswalk only.

• A Study of Daily Rifapentine Combined With Isoniazid (1HP) for Tuberculosis Prevention in Children Less Than 13 Years of Age With and Without HIV
  Not yet recruiting · Phase 1 · Phase 2 · Interventional · 144 enrolled · National Institute of Allergy and Infectious Diseases (NIAID)
  NCT07124559updated 2026-06-12
• Relevance of Isoniazid Dosage in Adults Treated for Tuberculosis
  Completed · Observational · 112 enrolled · Centre Hospitalier Universitaire, Amiens
  NCT06054334updated 2026-06-12
• Doxycycline Host-directed Therapy to Improve Lung Function and Decrease Tissue Destruction in Pulmonary Tuberculosis
  Recruiting · Phase 3 · Interventional · 150 enrolled · National University Hospital, Singapore
  NCT05473520updated 2026-06-09
• Comparative Trial Between Ainuovirine(ANV)/Lamivudine(3TC)/Tenofovir(TDF) and Efavirenz(EFV)/Lamivudine/Tenofovir Regimens
  Not yet recruiting · Phase 4 · Interventional · 60 enrolled · Shanghai Public Health Clinical Center
  NCT07631897updated 2026-06-08
• Evaluating Urine Isoniazid Testing to Detect Nonadherence to Tuberculosis Medications in India
  Enrolling by invitation · Interventional · 900 enrolled · Tufts University
  NCT06526221updated 2026-06-04
• Bedaquiline Roll-out Evidence in Contacts and People Living With HIV to Prevent TB
  Recruiting · Phase 2 · Phase 3 · Interventional · 2,530 enrolled · Johns Hopkins University
  NCT06568484updated 2026-06-03
• Trial of a Six-Month Regimen of High-Dose Rifampicin, High-Dose Isoniazid, Linezolid, and Pyrazinamide Versus a Standard Nine-Month Regimen for the Treatment of Adults and Adolescents With Tuberculous Meningitis
  Recruiting · Phase 2 · Interventional · 330 enrolled · National Institute of Allergy and Infectious Diseases (NIAID)
  NCT05383742updated 2026-06-02
• Adjunctive Doxycycline for Central Nervous System Tuberculosis
  Recruiting · Phase 2 · Interventional · 200 enrolled · National University Hospital, Singapore
  NCT06446245updated 2026-06-01
• Shortened Regimen for Drug-susceptible TB in Children
  Recruiting · Phase 3 · Interventional · 860 enrolled · Johns Hopkins University
  NCT06253715updated 2026-06-01
• STeroids and Enhanced Spectrum Antibiotics for the Treatment of Patients in Africa With Refractory Sepsis
  Not yet recruiting · Phase 3 · Interventional · 344 enrolled · University of Virginia
  NCT07332325updated 2026-06-01

CPIC-curated drug–gene pairs for Isoniazid. Levels describe the strength of curated evidence and guideline status — never a recommendation to test or to adjust therapy.

• NAT2CPIC C (provisional)ClinPGx 1BFDA label: Informative PGx

Frequently asked questions

How does Isoniazid work?

Isoniazid inhibits the synthesis of mycoloic acids, an essential component of the bacterial cell wall. At therapeutic levels isoniazid is bactericidal against actively growing intracellular and extracellular Mycobacterium tuberculosis organisms.

What is Isoniazid used for?

According to FDA labeling, Isoniazid carries indications including: Isoniazid tablets, USP are recommended for all forms of tuberculosis in which organisms are susceptible. However, active tuberculosis must be treated with multiple concomitant anti-tuberculosis medications to prevent the emergence of drug resistance.. This is a reference summary of labeled uses, not medical advice or a treatment recommendation.

What class of drug is Isoniazid?

Isoniazid is classified as Hydrazides, Antimycobacterial, Unknown Cellular or Molecular Interaction.

What are the contraindications for Isoniazid?

Isoniazid labeling lists contraindications including: Isoniazid is contraindicated in patients who develop severe hypersensitivity reactions, including drug-induced hepatitis; previous isoniazid-associated hepatic injury; severe adverse reactions to isoniazid such as drug fever, chills, arthritis; and acute liver disease of any etiology.. Always consult the full prescribing information and a clinician.