Isoniazid

Prescription ·Exploratory record · not publication-reviewed ·Updated July 13, 2026

Isoniazid is a first-line antibiotic used to treat and prevent tuberculosis caused by Mycobacterium tuberculosis. It is highly bactericidal against actively dividing organisms and is given both for latent infection (as monotherapy) and active disease (in combination with other agents). It is one of the most important drugs in modern tuberculosis therapy.

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Publication status

Exploratory record, not a reviewed medical publication.

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This generated database record has not completed a claim-level review by a qualified human medical reviewer. Bibliography links and evidence labels are not approval. The page remains available for reference and is excluded from search indexing.

In short

What the research says.

A quick, data-only summary. The full evidence, dosing, and sources are below.

Isoniazid is a first-line antibiotic used to treat and prevent tuberculosis caused by Mycobacterium tuberculosis. NutriStack rates the supporting evidence as strong. Common adult dosing is Active TB: 5 mg/kg (up to 300 mg) once daily, or 15 mg/kg (up to 900 mg) two to three times weekly. Latent TB: 300 mg once daily, or 900 mg twice weekly with directly observed therapy., though a prescriber sets the actual dose. With long-term use it can deplete vitamin b6, vitamin b6 (pyridoxine), niacin (vitamin b3). This profile indexes 4 sources.

What it's good for

Treatment of active pulmonary and extrapulmonary tuberculosis (in combination regimens)^1,3
Treatment of latent tuberculosis infection^1,3
Prevention of tuberculosis in high-risk exposed individuals^1,3

What to watch for

Peripheral neuropathy (numbness, tingling, paresthesias of hands and feet, related to vitamin B6 depletion)
Hepatotoxicity (elevated transaminases, hepatitis, rarely fatal liver failure)
Nausea, vomiting, and epigastric distress
Acute liver disease or prior isoniazid-associated hepatic injury^1,2
Severe hypersensitivity reaction to isoniazid (including drug-induced hepatitis, fever, chills, arthritis)^2,1

The bottom line

Evidence rating strong. Most-documented uses: treatment of active pulmonary and extrapulmonary tuberculosis (in combination regimens), treatment of latent tuberculosis infection, prevention of tuberculosis in high-risk exposed individuals. 4 sources indexed (1980–2016), with 0 interaction records on file.

The science

How it works, mechanistically.

Core mechanism

Isoniazid is a prodrug activated by the mycobacterial enzyme KatG (catalase-peroxidase). The activated form inhibits InhA, an enoyl-acyl carrier protein reductase, blocking the synthesis of mycolic acids that are essential components of the mycobacterial cell wall. The resulting disruption of cell wall biosynthesis is bactericidal against replicating organisms. Structurally a pyridine analogue, isoniazid also competes with pyridoxine (vitamin B6) and interferes with its conversion to the active coenzyme pyridoxal 5'-phosphate, which underlies its characteristic depletion of B6 and the related impairment of niacin (vitamin B3) synthesis.^3,1

Class

Antitubercular antibiotic

Absorption

Best on an empty stomach

Dosing

Dosing & protocol.

Common range

Active TB: 5 mg/kg (up to 300 mg) once daily, or 15 mg/kg (up to 900 mg) two to three times weekly. Latent TB: 300 mg once daily, or 900 mg twice weekly with directly observed therapy.

Recommended form

Oral tablet (also available as oral solution/syrup and injectable solution)

Best absorbed on an empty stomach, at least 1 hour before or 2 hours after meals; food, and especially high-fat or high-carbohydrate meals, reduces and delays absorption. Antacids containing aluminum should be separated by at least 1 hour. May be taken with food if gastrointestinal upset occurs.

Depletions

What it depletes.

Nutrients this medication can lower over time, and what to replace.

Vitamin B6

Significant

Isoniazid antagonizes pyridoxine metabolism and increases risk of pyridoxine-responsive peripheral neuropathy.

Replace Vitamin B6Monitor Clinical neuropathy assessment; pyridoxal 5-phosphate if availableOnset Weeks to months, sooner in high-risk patients

Vitamin B6 (Pyridoxine)

Significant

Isoniazid is a hydrazide derivative that reacts directly with pyridoxal and pyridoxal-5'-phosphate to form isoniazid-pyridoxal hydrazones, which are inactive and rapidly excreted in the urine. Isoniazid also inhibits the enzyme pyridoxine phosphokinase, blocking conversion of dietary pyridoxine to its active coenzyme form. The combined effect functionally depletes active vitamin B6, impairing pyridoxal-5'-phosphate-dependent reactions including the synthesis of neurotransmitters and heme.

Replace Pyridoxine (Vitamin B6)Monitor Plasma pyridoxal-5'-phosphate (PLP); clinical monitoring for signs of peripheral neuropathy (paresthesias, numbness)Onset Functional depletion can begin within weeks of starting therapy; peripheral neuropathy from B6 deficiency typically emerges over weeks to months, with higher risk at doses of 5 mg/kg/day or more and in malnourished, diabetic, alcoholic, pregnant, uremic, or slow-acetylator patients.

Niacin (Vitamin B3)

Moderate

Niacin can be synthesized endogenously from the amino acid tryptophan via a pyridoxal-5'-phosphate (vitamin B6)-dependent pathway (the kynurenine pathway). By depleting active vitamin B6, isoniazid impairs this conversion of tryptophan to niacin. Isoniazid is also a structural analog of niacinamide and can interfere with niacin/NAD metabolism. The net effect can precipitate a niacin-deficiency (pellagra-like) state, particularly in patients with marginal dietary intake.

Replace Niacinamide (Nicotinamide)Monitor Urinary N1-methylnicotinamide and 2-pyridone metabolites; clinical monitoring for pellagra signs (dermatitis, diarrhea, dementia/glossitis)Onset Pellagra-like manifestations (dermatitis, glossitis, neuropsychiatric changes) have been reported after weeks to months of therapy, more often in malnourished or low-dietary-niacin populations.

Full Isoniazid depletion and interaction guide →

Safety

Full safety detail.

Side effects

Peripheral neuropathy (numbness, tingling, paresthesias of hands and feet, related to vitamin B6 depletion)
Hepatotoxicity (elevated transaminases, hepatitis, rarely fatal liver failure)
Nausea, vomiting, and epigastric distress
Rash and hypersensitivity reactions
Dizziness and CNS effects
Pyridoxine-responsive sideroblastic anemia (rare)
Drug-induced lupus (rare)
Pellagra-like dermatitis from niacin interference (rare)

Contraindications

Acute liver disease or prior isoniazid-associated hepatic injury^1,2
Severe hypersensitivity reaction to isoniazid (including drug-induced hepatitis, fever, chills, arthritis)^2,1
Use with caution in patients with peripheral neuropathy, chronic alcohol use, malnutrition, diabetes, HIV, pregnancy, and renal impairment⁴

Sources

Sources, by evidence tier.

Numbered references. Citations throughout the page link here.

Reviews & position papers

1Official ATS/CDC/IDSA Clinical Practice Guidelines: Treatment of Drug-Susceptible TuberculosisNahid P, et al. · Clinical Infectious Diseases · 2016
Isoniazid remains a first-line agent for both latent and active drug-susceptible tuberculosis as part of standard multidrug regimens.
2An official ATS statement: hepatotoxicity of antituberculosis therapySaukkonen JJ, et al. · American Journal of Respiratory and Critical Care Medicine · 2006
Isoniazid-associated hepatotoxicity increases with age, alcohol use, and concurrent hepatotoxins; baseline and periodic liver function monitoring is recommended.
3Isoniazid: mechanism of action and resistanceZhang Y, et al. · The Lancet · 1992
Mutations in katG and inhA confer isoniazid resistance, confirming the prodrug-activation and mycolic-acid-synthesis-inhibition mechanism.
4Pyridoxine for the prevention of isoniazid-induced peripheral neuropathySnider DE · Tubercle · 1980
Supplemental pyridoxine (typically 25-50 mg daily) prevents peripheral neuropathy in patients at risk during isoniazid therapy.

FAQ

Common questions.

Quick answers about Isoniazid, drawn from the data on this page.

What is Isoniazid?

What is Isoniazid used for?

Commonly cited benefits of Isoniazid include: Treatment of active pulmonary and extrapulmonary tuberculosis (in combination regimens); Treatment of latent tuberculosis infection; Prevention of tuberculosis in high-risk exposed individuals. NutriStack rates the overall evidence as strong.

What is a typical dose of Isoniazid?

A typical adult dose of Isoniazid is Active TB: 5 mg/kg (up to 300 mg) once daily, or 15 mg/kg (up to 900 mg) two to three times weekly. Latent TB: 300 mg once daily, or 900 mg twice weekly with directly observed therapy.. The commonly recommended form is Oral tablet (also available as oral solution/syrup and injectable solution). These are general ranges, not personalized advice; confirm the right dose with a clinician.

What are the side effects of Isoniazid?

Reported side effects include peripheral neuropathy (numbness, tingling, paresthesias of hands and feet, related to vitamin b6 depletion), hepatotoxicity (elevated transaminases, hepatitis, rarely fatal liver failure), nausea, vomiting, and epigastric distress, rash and hypersensitivity reactions, dizziness and cns effects, pyridoxine-responsive sideroblastic anemia (rare). This is educational information; check with a healthcare professional before use.

How strong is the evidence for Isoniazid?

NutriStack rates this as Strong, meaning multiple high-quality meta-analyses or systematic reviews converge on the same finding. Full tier criteria are at https://nutristackapp.com/methodology/evidence-tiers.

Use this with your stack

Isoniazid in NutriStack.

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