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Isoniazid oral

Updated 2 Feb 2023 | Isoniazid


Tablets containing isoniazid

Drugs List

  • isoniazid 100mg tablets
  • isoniazid 50mg tablets
  • Therapeutic Indications


    Tuberculosis - extra pulmonary
    Tuberculosis - pulmonary

    Unlicensed Uses

    Tuberculosis - prophylaxis



    Treatment of tuberculosis
    6 months unsupervised treatment
    Typically 4mg/kg to 5mg/kg daily (maximum 300mg daily).
    Up to 10mg/kg daily may be given particularly during the first one to two weeks of treatment of tuberculous meningitis.

    6 months intermittent supervised treatment
    15mg/kg (maximum dose 900mg) three times weekly.

    Prophylaxis of tuberculosis in susceptible close contacts or those who have become tuberculin positive (unlicensed)
    300 mg daily for six months.
    300mg daily with rifampicin for three months.


    Treatment of tuberculosis
    5mg/kg to 20mg/kg daily in single or divided doses.

    The following alternative dosing schedule may be suitable:
    6 months unsupervised treatment
    10mg/kg (maximum 300mg) once daily.
    6 months intermittent supervised treatment
    15mg/kg (maximum 900mg) three times weekly.

    Prophylaxis of tuberculosis in susceptible close contacts or those who have become tuberculin positive (unlicensed)
    Children aged 12 to 18 years
    300mg daily for six months
    300mg daily with rifampicin for three months.

    Children aged 1 month to 12 years
    10mg/kg daily (maximum 300mg daily) for six months.
    10mg/kg daily (maximum 300mg daily) with rifampicin for three months.


    Treatment of congenital tuberculosis (unlicensed)
    10mg/kg daily for six months.

    Prophylaxis of tuberculosis in susceptible close contacts or those who have become tuberculin positive (unlicensed)
    10mg/kg daily for six months.

    Patients with Renal Impairment

    The Renal Drug Handbook suggests the following doses in patients with renal impairment:

    Glomerular filtration rate 10ml/minute or above: Dose as in normal renal function.
    Glomerular filtration rate below 10ml/minute: 200mg to 300mg daily.


    Drug induced hepatic disorder

    Precautions and Warnings

    Acute porphyria
    Diabetes mellitus
    Epileptic disorder
    Glucose-galactose malabsorption syndrome
    Hepatic impairment
    History of psychosis
    Lactose intolerance
    Positive HIV status
    Renal impairment - glomerular filtration rate below 10ml/minute
    Slow acetylator status

    Consult national/regional policy on the use of anti-infectives
    Must be used in combination with other anti-tuberculous drugs
    Contains lactose
    Advise patient to take at least 30 minutes before a meal
    Monitor hepatic function before treatment and regularly during treatment
    Adverse effects may be seen after ingestion of high-tyramine foods/drinks
    Advise patients to discontinue therapy if signs of hepatotoxicity occur
    Advise patients to report signs of hepatic damage (malaise, jaundice etc.)
    Consider treatment with pyridoxine to prevent peripheral neuritis
    Discontinue if hepatitis develops
    May cause convulsions
    Discontinue if AST level exceeds 3 times the upper limit of normal
    Discontinue if substantial increase in bilirubin occurs
    Discontinue if symptoms of hepatic disease occur
    Advise patient to seek medical advice before taking paracetamol products
    Advise patient of importance of full compliance

    Specialist advice should be sought about tuberculosis treatment in immunocompromised patients. Dosage regimens should be chosen carefully and potentially hazardous interactions should be avoided.

    Isoniazid may increase the formation of toxic metabolites of paracetamol if paracetamol is taken during isoniazid treatment. Advise patients that they should limit the use of paracetamol-containing products during treatment with isoniazid and, preferably, seek medical advice before taking paracetamol-containing products.

    Patients receiving isoniazid may experience adverse effects (such as headache, sweating, palpitations, flushing and hypotension) after consuming certain foods or drinks. Tyramine-containing foods may cause an interaction due to the weak monoamine oxidase inhibiting activity of isoniazid and high-tyramine foods such as cheese, red wine, lager and preserved foods should be considered if a patient presents with such a reaction. Isoniazid may also inhibit diamine oxidase, causing an enhanced response to histamine-containing foods such as cheese or fish that is not fresh. The diet of the patient should be examined and advice to avoid such foodstuffs should be given in the event of such a reaction.

    Pregnancy and Lactation


    Isoniazid should be only be used in pregnancy when the potential benefit justifies the potential risk to the foetus. If used in pregnancy, pyridoxine supplementation is recommended.

    It is considered that untreated tuberculosis is a greater hazard to a pregnant woman and her foetus than treatment with isoniazid.

    It is known that isoniazid crosses the human placenta to the foetus. Briggs states that isoniazid does not appear to be a human teratogen. Schaefer states that isoniazid is the drug of choice for prophylaxis and treatment of tuberculosis in pregnancy and recommends combination with pyridoxine (vitamin B6) and monthly liver function tests. Animal studies in mice, rats and rabbits have not revealed teratogenic effects, but embryocidal effects were observed in rats and rabbits.

    The use of all medication in pregnancy should be avoided whenever possible; particularly in the first trimester. Non-drug treatments should also be considered. When essential, a medication with the best safety record over time should be chosen, employing the lowest effective dose for the shortest possible time. Polypharmacy should be avoided. Teratogens taken in the pre-embryonic period, often quoted as lasting until 14-17 days post-conception, are believed to have an all-or-nothing effect. Where drugs have a short half-life, and when the date of conception is certain, this may allow women to be reassured where drug exposure has occurred within this time frame. Further advice may be available from the UK National Teratology Information Service (NTIS) and through ToxBase, available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Licensed in pregnancy? - No

    Recommended for use in pregnancy? - Drug of choice for prophylaxis and treatment of tuberculosis in pregnancy


    The manufacturer advises caution when treating with isoniazid during breastfeeding.

    At least one review concludes that women can safely breastfeed their infants while taking isoniazid if the infant is periodically examined for signs and symptoms of peripheral neuritis and hepatitis. The Centres for Disease Control and Prevention (USA) state that breastfeeding should not be discouraged in patients taking isoniazid. Low levels of isoniazid are excreted in breast milk, it is unlikely to cause adverse reactions in infants. The concentration of isoniazid in milk is not considered sufficient for treatment of tuberculosis in the breastfed infant.

    Schaefer concludes that isoniazid (in combination with 0.5 to 1 mg of vitamin B6 prophylaxis per day for the infant), rifampicin and pyrazinamide are the tuberculostatics of choice during breastfeeding. Ethambutol is also acceptable.

    Infant should be monitored for toxicity including hepatitis and vision changes. Administration of pyridoxine to the breastfeeding mother and infant may be considered.

    Neonates, infants born prematurely, those with low birth weight, those with an unstable gastrointestinal function or who have serious illnesses may require special consideration. For any infant, if a drug is prescribed to the nursing mother, it should be at the lowest practical dose and for the shortest time. When drug administration is unavoidable and breastfeeding is to continue, minimisation of exposure of the infant to the drug may sometimes be achieved by timing the maternal doses to just after a feeding episode. Infants exposed to drugs via breast milk should be monitored for unusual signs or symptoms. Interactions between the drug received by the infant from the mother's milk and medication prescribed for the infant should also be considered, for example, when the drug given to the infant may prevent metabolism of the drug received via breast milk.
    Specialist advice is available from the UK Drugs in Lactation Advisory Service at

    Drug excreted in breast milk? - Yes

    Considered suitable or recommended by manufacturer? - Yes

    Side Effects

    Acute pancreatitis
    Aplastic anaemia
    Difficulty in micturition
    Dry mouth
    Elevation of liver enzymes
    Erythema multiforme
    Fulminant hepatitis
    Gastro-intestinal disturbances
    Haemolytic anaemia
    Hearing loss
    Hepatic damage
    Hepatic necrosis
    Hypersensitivity reactions
    Interstitial pneumonitis
    Lupus erythematosus-like syndrome
    Mood changes
    Optic neuritis
    Peripheral neuropathy
    Personality change
    Psychotic episodes
    Stevens-Johnson syndrome
    Systemic lupus erythematosus
    Toxic epidermal necrolysis
    Withdrawal symptoms

    Withdrawal Symptoms and Signs

    On discontinuation of treatment, effects such as headache, insomnia, excessive dreaming, irritability or nervousness may occur.


    It is strongly recommended that the UK National Poisons Information Service be consulted on cases of suspected or actual overdose where there is doubt over the degree of risk or about appropriate management.

    The following number will direct the caller to the relevant local centre (0844) 892 0111

    Information may be obtained if you have access to ToxBase the primary clinical toxicology database of the National Poisons Information Service. This is available via password on the internet ( ) or if this is unavailable at the backup site ( ).

    Further Information

    Last Full Review Date: April 2013

    Reference Sources

    Drugs During Pregnancy and Lactation: Treatment Options and Risk Assessment, 2nd edition (2007) ed. Schaefer, C., Peters, P. and Miller, R. Elsevier, London.

    Drugs in Pregnancy and Lactation: A Reference Guide to Fetal and Neonatal Risk, 9th edition (2011) ed. Briggs, G., Freeman, R. and Yaffe, S. Lippincott Williams & Wilkins, Philadelphia.

    Martindale: The Complete Drug Reference, 37th edition (2011) ed. Sweetman, S. Pharmaceutical Press, London.

    Medications and Mothers' Milk, 14th Edition (2010) Hale, T. Hale Publishing, Amarillo, Texas.

    Summary of Product Characteristics: Isoniazid tablets 50 mg. Focus Pharmaceuticals Limited. Revised March 2010.
    Summary of Product Characteristics: Isoniazid tablets 100 mg. Focus Pharmaceuticals Limited. Revised March 2010.

    The Renal Drug Handbook. 3rd edition. (2009) ed. Ashley, C and Currie, Radcliffe Publishing Ltd, Abingdon.

    NICE Evidence Services Available at: Last accessed: 12 September 2017

    The Drug Database for acute Porphyria (NAPOS)
    Available at:
    Isoniazid Last revised: October 1, 2004
    Last accessed: July 15, 2010

    US National Library of Medicine. Toxicology Data Network. Drugs and Lactation Database (LactMed).
    Available at:
    Isoniazid. Last revised: October 2, 2012
    Last accessed: April 17, 2013

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    Medscape UK | Univadis prescription drug monographs & interactions are based on FDB Multilex Content

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