Isoniazid Schedule (India)

Schedule H

Isoniazid Routes

Oral, Intramuscular, Intravenous

Isoniazid Formulations

Formulation Strength

Tablet 100 mg, 300 mg

Syrup 50 mg/5 mL

Injection 100 mg/mL (1 mL and 5 mL ampoules)

Fixed-Dose Combinations (FDCs) available under NTEP/NLEM:

Isoniazid + Rifampicin (HR)

Isoniazid + Rifampicin + Pyrazinamide (HRZ)

Isoniazid + Rifampicin + Pyrazinamide + Ethambutol (HRZE)

Paediatric dispersible FDCs (various weight-band formulations)

Isoniazid Adult indications

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

Pulmonary and Extrapulmonary Tuberculosis (Active Disease)

As part of multi-drug regimen under NTEP guidelines. Never use as monotherapy for active TB.

Parameter Recommendation

Starting dose 5 mg/kg orally once daily (usual adult dose: 300 mg)

Titration Not applicable (weight-band based fixed dosing)

Usual maintenance dose 5 mg/kg once daily (300 mg for adults ≥30 kg)

Maximum dose 300 mg/day

Weight-Band Dosing for Adults (NTEP Guidelines):

Body Weight Daily Isoniazid Dose

30–39 kg 225 mg once daily

40–54 kg 300 mg once daily

55–69 kg 300 mg once daily

≥70 kg 300 mg once daily

Duration per NTEP:

New drug-susceptible TB: 6 months (2HRZE + 4HR)

Previously treated: As per drug susceptibility testing

TB meningitis/bone TB: 12 months (extended continuation phase)

Clinical Notes:

Always use in combination as part of HRZE regimen

Preferably use fixed-dose combinations (FDCs) to ensure adherence

Administer on empty stomach for optimal absorption (1 hour before or 2 hours after meals)

Always co-prescribe pyridoxine (vitamin B6) 10–25 mg/day in high-risk patients (HIV, diabetes, malnutrition, pregnancy, alcoholism)

Latent Tuberculosis Infection (LTBI) / TB Preventive Therapy (TPT)

Per NTEP and ICMR guidelines for preventive therapy.

Regimen Options:

Regimen Dose Duration Target Population

6H (Isoniazid monotherapy) 300 mg once daily 6 months PLHIV, close contacts, immunosuppressed

9H (Isoniazid monotherapy) 300 mg once daily 9 months Alternative duration per clinical judgment

3HP (Isoniazid + Rifapentine) INH 15 mg/kg (max 900 mg) + Rifapentine weekly 3 months (12 doses) PLHIV, contacts (if DOT possible)

3HR (Isoniazid + Rifampicin) INH 10 mg/kg (max 300 mg) + RIF daily 3 months Alternative short-course regimen

Parameter Recommendation (6H Regimen)

Starting dose 300 mg orally once daily

Titration Not applicable

Usual maintenance dose 300 mg once daily

Maximum dose 300 mg/day

Clinical Notes:

Always rule out active TB before initiating preventive therapy (symptom screen, chest X-ray)

Always co-prescribe pyridoxine 10–25 mg/day

Priority populations: PLHIV, household contacts <5 years, immunosuppressed patients with positive TST/IGRA

Monitor LFTs at baseline and during therapy

Secondary Indications – Adults (Off-label)

Not applicable — No established off-label indications outside TB-related use in India.

Isoniazid Paediatric indications

PAEDIATRIC DOSING (Specialist Only)

⚠️ Always use in combination therapy for active TB — monotherapy causes rapid resistance.

⚠️ Paediatric dispersible FDCs preferred under NTEP for accurate weight-band dosing.

Primary Indications (Approved/Standard Use in India)

Active Tuberculosis (Pulmonary and Extrapulmonary)

As part of HRZE multi-drug regimen per NTEP/IAP guidelines.

Weight-Band Dosing (NTEP Paediatric Guidelines):

Weight Band Isoniazid Dose (Once Daily)

4–7 kg 50 mg

8–11 kg 100 mg

12–15 kg 150 mg

16–24 kg 200 mg

25–29 kg 250 mg

≥30 kg 300 mg (adult dosing)

General Paediatric Dosing:

Parameter Recommendation

Starting dose 10 mg/kg orally once daily

Titration Not applicable

Usual maintenance dose 10 mg/kg once daily

Maximum dose 300 mg/day

Duration:

Drug-susceptible pulmonary TB: 6 months (2HRZE + 4HR)

TB meningitis/bone TB: 12 months

Clinical Notes:

Use paediatric dispersible FDC tablets for children <25 kg

Syrup formulation (50 mg/5 mL) available for precise dosing in infants

Always co-prescribe pyridoxine in malnourished, HIV-positive, or exclusively breastfed children

Administer all drugs together as single daily dose

Latent TB Infection (LTBI) / TB Preventive Therapy

Parameter Recommendation

Starting dose 10 mg/kg orally once daily

Titration Not applicable

Usual maintenance dose 10 mg/kg once daily

Maximum dose 300 mg/day

Duration: 6 months (6H regimen)

Eligibility per NTEP:

Household contacts <5 years of pulmonary TB patients

Children living with HIV

Children on immunosuppressive therapy

Secondary Indications – Paediatrics (Off-label)

Not applicable.

Age Restrictions:

Infants <12 weeks: Use only under specialist supervision (neonatologist/paediatric pulmonologist) in TB exposure scenarios

Pyridoxine supplementation mandatory in all infants on isoniazid

Safety Monitoring in Paediatrics:

Baseline LFTs in children with HIV, malnutrition, or hepatic disease

Clinical monitoring for jaundice, hepatomegaly, vomiting

Monitor for peripheral neuropathy symptoms

Weight monitoring for dose adjustments

Isoniazid Renal Adjustments

eGFR (ml/min/1.73m²)	Recommendation
eGFR (ml/min/1.73m²)	Recommendation
eGFR (ml/min/1.73m²)	Recommendation
Haemodialysis	Administer 300 mg after dialysis on dialysis days; supplement pyridoxine
Peritoneal dialysis	No dose adjustment required

Note: Isoniazid and its metabolites are removed by haemodialysis — schedule dose post-dialysis to avoid subtherapeutic levels.

Isoniazid Hepatic adjustment

Hepatic Impairment	Recommendation
Mild impairment (Child-Pugh A)	Standard dose; monitor LFTs at baseline and every 2–4 weeks initially
Moderate impairment (Child-Pugh B)	Use with caution; consider dose reduction if LFTs rise >3× ULN; close monitoring every 1–2 weeks
Severe impairment (Child-Pugh C)	/ Decompensated cirrhosis Avoid unless benefit clearly outweighs risk; specialist decision only; consider alternative regimens without isoniazid if available

Drug-Induced Liver Injury (DILI) Management:

If ALT >5× ULN (asymptomatic) or >3× ULN with symptoms: Stop isoniazid immediately

Rechallenge only after LFTs normalise; reintroduce at 50% dose with close monitoring

Consider modified regimens (e.g., streptomycin-based) in patients with severe hepatotoxicity

Isoniazid Contraindications

Known hypersensitivity to isoniazid

Active acute hepatitis or acute liver failure

History of severe isoniazid-induced hepatotoxicity

History of severe adverse CNS reactions (psychosis, seizures) attributed to prior isoniazid use

Concurrent use with disulfiram (severe CNS toxicity risk)

Isoniazid Cautions

Pre-existing chronic liver disease or chronic hepatitis — increased hepatotoxicity risk

Chronic alcoholism — additive hepatotoxic potential; higher neuropathy risk

HIV infection — increased risk of peripheral neuropathy and hepatotoxicity

Malnutrition or vitamin B6 deficiency — mandatory pyridoxine supplementation

Diabetes mellitus — increased peripheral neuropathy risk

Epilepsy or seizure disorder — may lower seizure threshold

Slow acetylator phenotype (common in Indian population) — higher drug levels and toxicity risk

Concurrent hepatotoxic drugs (rifampicin, pyrazinamide, methotrexate, antiretrovirals)

Pregnancy — use with pyridoxine supplementation

Age >35 years — increased hepatotoxicity risk; enhanced LFT monitoring required

Isoniazid Pregnancy

Parameter Recommendation

Risk Category Generally considered safe; benefits outweigh risks for TB treatment/prevention

Overall Recommendation Safe and indicated for TB treatment throughout pregnancy

Preferred Alternatives No alternative needed; isoniazid is first-line agent for TB in pregnancy

When to use All trimesters; do not defer TB treatment due to pregnancy; TPT can be initiated during pregnancy in high-risk women (PLHIV)

Monitoring Maternal LFTs (baseline and every trimester); clinical symptoms of hepatitis; pyridoxine 25–50 mg/day mandatory

Special Considerations:

Pyridoxine supplementation prevents neonatal seizures and maternal neuropathy

Third-trimester hepatotoxicity risk may be slightly increased — enhanced vigilance required

Isoniazid Lactation

Parameter Recommendation

Compatibility Compatible with breastfeeding

Drug Levels in Milk Low (approximately 20% of maternal plasma concentration reaches infant)

Preferred Alternatives None needed; continue isoniazid during breastfeeding

Infant Monitoring Observe for adequate weight gain, feeding patterns, jaundice; rare hepatotoxicity reported

Special Considerations:

Pyridoxine supplementation recommended for both mother and exclusively breastfed infant

Amount of drug in milk insufficient to provide therapeutic effect or prophylaxis in infant — treat infant separately if indicated

Isoniazid Elderly

Parameter Recommendation

Starting Dose Standard adult dose (5 mg/kg/day, usually 300 mg)

Titration Not applicable; however, lower threshold for holding drug if LFT abnormalities

Special Risks Increased hepatotoxicity risk (age >35 years is independent risk factor); peripheral neuropathy; cognitive changes; polypharmacy interactions

Monitoring LFTs at baseline, 2 weeks, 4 weeks, then monthly; mandatory pyridoxine supplementation; clinical surveillance for confusion, neuropathy

Isoniazid Major drug interactions

Interacting Drug Mechanism/Effect Management

Phenytoin Isoniazid inhibits CYP2C19 → increased phenytoin levels → toxicity (ataxia, nystagmus, confusion) Monitor phenytoin levels; may need 25–50% dose reduction

Carbamazepine Isoniazid inhibits carbamazepine metabolism → increased levels → toxicity Monitor carbamazepine levels; clinical surveillance for toxicity

Disulfiram Additive CNS toxicity → psychosis, coordination difficulties Avoid combination; if essential, close neuropsychiatric monitoring

Rifampicin Additive hepatotoxicity; both are hepatotoxic first-line TB drugs Use together as standard practice but with enhanced LFT monitoring; stop both if significant hepatotoxicity

Paracetamol (chronic/high dose) Isoniazid induces CYP2E1 → increased toxic paracetamol metabolite → hepatotoxicity Limit paracetamol to <2 g/day during isoniazid therapy

Isoniazid Moderate drug interactions

Interacting Drug Effect Management

Theophylline Isoniazid may increase theophylline levels Monitor theophylline levels if used chronically

Warfarin Variable effect on metabolism; may increase INR Monitor INR closely; adjust warfarin dose as needed

Efavirenz/Nevirapine Additive hepatotoxicity; possible CYP interaction Monitor LFTs; can be used together with vigilance

Valproate May increase valproate levels Monitor valproate levels

Ketoconazole/Fluconazole Additive hepatotoxicity Monitor LFTs

Aluminium-containing antacids Reduced isoniazid absorption Separate administration by at least 1 hour

Prednisolone/Corticosteroids Isoniazid may reduce corticosteroid efficacy slightly May need minor dose adjustment in some cases

Alcohol Increased hepatotoxicity risk; accelerated isoniazid metabolism Advise avoidance or strict limitation of alcohol intake

Isoniazid Common Adverse effects

Peripheral neuropathy (dose-dependent; preventable with pyridoxine)

Hepatotoxicity (elevated ALT/AST — usually transient and asymptomatic)

Gastrointestinal: nausea, vomiting, epigastric discomfort, anorexia

Cutaneous: rash, acneiform eruptions, pruritus

CNS: irritability, insomnia, restlessness, headache

Mild drug fever

Isoniazid Serious Adverse effects

Adverse Effect Clinical Significance

Fulminant hepatitis / Acute liver failure Potentially fatal; requires immediate discontinuation; hospitalisation for supportive care

Severe peripheral neuropathy May be irreversible if not detected early; stop isoniazid; high-dose pyridoxine

Stevens-Johnson Syndrome / TEN Rare; immediate discontinuation and dermatology consultation

Seizures Risk increased in B6 deficiency or overdose; pyridoxine is antidote

Drug-induced lupus Rare; ANA positivity; discontinue if clinical lupus develops

Psychosis / Encephalopathy Rare; dose-dependent; more common in slow acetylators

Optic neuritis Rare; visual disturbances require immediate ophthalmology evaluation

Pellagra Rare; due to niacin depletion; supplementation may be needed

Isoniazid Monitoring requirements

Timing	Parameters
Baseline	LFTs (ALT, AST, bilirubin), symptom screening for liver disease, HIV status, pregnancy test in women of childbearing age, nutritional status assessment

High-risk patients (first 2–4 weeks) LFTs at 2 weeks and 4 weeks; clinical assessment for hepatitis symptoms

Monthly during intensive phase Clinical symptom check (jaundice, anorexia, nausea, dark urine); LFTs if symptomatic or high-risk

Continuation phase Monthly clinical assessment; LFTs every 1–2 months if on concurrent hepatotoxic drugs

Long-term/TPT LFTs at baseline, 1 month, 3 months, then as needed; symptom-based monitoring

High-Risk Groups Requiring Enhanced Monitoring:

Age >35 years

Chronic alcoholism

HIV infection

Pre-existing liver disease

Concurrent hepatotoxic drugs

Pregnancy

Malnutrition

Clinical Symptoms to Monitor:

Prodromal hepatitis: anorexia, nausea, fatigue, malaise, dark urine

Peripheral neuropathy: numbness, tingling, burning in extremities

CNS effects: confusion, behavioural changes, seizures

Isoniazid Brands in India

Single-Agent Formulations:

ISONEX® (Lupin)

ISOKIN® (Cadila)

ISONIAZID® (Various generics)

I-NIZ® (Macleods)

Combinations with Pyridoxine:

ISOVIT® (Isoniazid + Pyridoxine)

Fixed-Dose Combinations (NTEP-Compliant):

Brand Name	Composition	Manufacturer
*	R-CINEX® (Isoniazid + Rifampicin) —	Lupin

AKURIT® (HRZE) — Lupin

FORECOX® (HRZE) — Macleods

Paediatric dispersible FDCs available through NTEP

Note: Government supply (NTEP) provides FDCs free of cost at designated TB centres.

Isoniazid Price range (INR)

Formulation	Approximate Price (per tablet)
Isoniazid 100 mg tablet ₹0.50–₹1.50 per tablet
Isoniazid 300 mg tablet ₹1.50–₹3 per tablet
Isoniazid syrup 50 mg/5 mL ₹20–₹35 per 60 mL bottle
Isoniazid injection 100 mg/mL ₹15–₹30 per ampoule Limited availability

Regulatory Notes:

Included in NLEM 2022 (essential medicine for TB)

Under NPPA price control

Free supply under NTEP at government facilities and DOTS centres

Isoniazid Clinical pearls

Pyridoxine is non-negotiable in high-risk patients: Always co-prescribe vitamin B6 (10–25 mg/day) for HIV-positive, diabetic, malnourished, pregnant, alcoholic, or elderly patients to prevent peripheral neuropathy.

Never monotherapy for active TB: Isoniazid monotherapy is reserved only for latent TB infection; for active disease, always use in combination per NTEP regimens.

Acetylator status matters: Slow acetylators (common in Indian population) have higher drug levels and increased risk of toxicity — be vigilant for adverse effects even at standard doses.

Hepatotoxicity is age-dependent: Risk increases significantly after age 35; enhanced LFT monitoring is mandatory in older adults and those with additional risk factors.

Symptom-based education is crucial: Counsel all patients to report immediately: loss of appetite, nausea, vomiting, dark urine, jaundice, or unusual fatigue — these may indicate hepatotoxicity before LFT abnormalities.

Phenytoin interaction is clinically significant: If patient requires both drugs, monitor phenytoin levels and watch for toxicity signs (ataxia, nystagmus); dose reduction usually needed.

Isoniazid Tags

isoniazid; tuberculosis; antitubercular; NTEP; latent TB; TPT; hepatotoxicity; peripheral neuropathy; pyridoxine; slow acetylator; NLEM India; pregnancy-compatible

Isoniazid Version

RxIndia v1.0 — 05 Jan 2025

Isoniazid Reference

CDSCO Approved Product Information

Indian Pharmacopoeia 2018

National TB Elimination Programme (NTEP) — Technical and Operational Guidelines (2021)

ICMR Guidelines on LTBI Management

API Textbook of Medicine (Tuberculosis Chapter)

IAP Guidelines on Paediatric Tuberculosis

AIIMS TB Management Protocols

WHO Consolidated Guidelines on Tuberculosis (India-adapted version)

MoHFW — Central TB Division Guidelines

RxIndia

The Drug Registry

Isoniazid

Pretomanid