Isoniazid 100 mg tablets – patient leaflet, side effects, dosage

1. What lsoniazid tablets are and what they are used for 2. What you need to know before you take

lsoniazid tablets

1. 3. How to take lsoniazid tablets
2. 4. Possible side effects
3. 5. How to store lsoniazid tablets
4. 6.
   1. 1.

      What lsoniazid tablets are and what they are used for

      lsoniazid is an antibiotic (antibacterial medicine) for treating infections. It belongs to a group of antibiotics called antituberculosis drugs and is used to treat and prevent tuberculosis (TB), an infectious disease mainly affecting the lungs.

2. What you need to know before you take lsoniazid tablets

Do not take lsoniazid tablets:

• if you are allergic to isoniazid or any of the other ingredients of this medicine (listed in section 6),
• if you have ever suffered from liver damage caused by a medicine, • If you have ever developed a severe skin rash or skin

peeling, blistering and/or mouth sores after taking Isoniazid tablets.

Warnings and precautions

Talk to your doctor or pharmacist before taking lsoniazid tablets:

• if you have or have had problems with your liver

  or kidneys,

• if you drink a lot of alcohol. It is also best to avoid

  drinking alcohol whilst you are taking this medicine, • if you are diabetic,

• if you have extra-pulmonary TB (outside the lungs), • if you have the HIV infection,
• if you have suffered mental disturbances (psychosis), • if you have malnutrition,

• if you have epilepsy or have ever had convulsions (fits), • if you are presently taking itraconazole (to treat fungal

  infections). It is not recommended to combine isoniazid and itraconazole.

Take special care with Isoniazid tablets

• Serious skin reactions such as Severe extensive skin

  damage (separation of the epidermis and superficial mucous membranes) (toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) and acute generalised exanthematous pustulosis (AGEP) have been reported in association with Isoniazid tablets treatment. Stop using Isoniazid tablets and seek medical attention immediately if you notice any of the symptoms described in section 4.

Other medicines and lsoniazid tablets

Tell your doctor or pharmacist if you are taking, have recently taken or might take any other medicines, including

medicines obtained without a prescription or herbal medicines.

soniazid may interact with

other medicines.

Please inform your doctor or

pharmacist if:

• you are taking another medicine

  to treat tuberculosis (TB)

  (e.g. para-aminosalicylic acid,

  rifampicin, cycloserine),

• you are taking disulfiram for

  alcohol dependence,

  • you are taking any medication for epilepsy (e.g.

    carbamazepine, primidone, phenytoin),

  • you are taking medication for HIV infection

    (e.g. stavudine, zalcitabine),

  • you are taking a vitamin B6 or B3 supplement, • you are taking medication for asthma or chronic obstructive pulmonary disease (e.g. theophylline), • you are taking medication for anxiety (e.g.

    benzodiazepines: diazepam, triazolam, chlorzoxazone), • you are taking medication for high blood pressure

    (e.g. propranolol),

  • you are taking drugs containing levodopa (used in the treatment of Parkinson’s disease),
  • you are taking cycloserine (used to treat tuberculosis and urinary tract infections),

  • you are taking ketoconazole or itraconazole

    (used to treat fungal infections).

lsoniazid tablets with food and drink

lsoniazid tablets should be taken preferably on an empty stomach, i.e. at least 30 minutes before a meal or 2 hours after a meal. Tablets must be swallowed whole and not chewed. lsoniazid may interact with foods containing histamine or tyramine (e.g. matured cheeses, cured meat, some fish like tuna, salmon and mackerel, wine and beer), causing symptoms including headache, sweating, flushing, fast, uneven or forceful heartbeat (palpitations), dizziness,

feel light-headed or faint (due to low

blood pressure).

These foods should be avoided if you are

receiving isoniazid. Your doctor will be

able to advise further.

Pregnancy, breast-feeding and fertility

If you are pregnant or breast-feeding,

think you may be pregnant or are

planning to have a baby, ask your doctor

or pharmacist for advice before taking

this medicine.

You may be given additional vitamin

supplementation if you are taking this

medicine whilst pregnant.

You and your baby may be given

No studies on the effects on the ability to drive and use machines have been performed. However, you may experience side-effects such as dizziness and confusion during treatment with isoniazid. Therefore, do not drive a car or operate machinery until you know how isoniazid affects you.

3. How to take lsoniazid tablets

Always take lsoniazid tablets exactly as your doctor has told you.

Important:

Your doctor will choose the dose that is right for you. Your dose will be shown clearly on the label that your pharmacist puts on your medicine.

If it does not, or you are not sure, ask your doctor or pharmacist.

Remember: lsoniazid tablets should not be taken with food. You should swallow lsoniazid tablets whole with a glass of water.

Adults

The usual dose of lsoniazid tablets is 4 to 5 mg per kilogram (kg) of your bodyweight per day, up to a maximum of 300 mg daily. This may be taken as a single dose or as divided doses throughout the day. Your doctor will tell you exactly how much medicine to take and when to take it. Higher doses (up to 10 mg per kg per day) may be used to treat tuberculous meningitis (tuberculosis causing inflammation of the brain’s membranes).

Elderly

If you are elderly, your doctor may tell you to take a slightly lower dose because your liver and kidneys are not working as well as they should.

Use in children

The usual dose for children above the age of three months is 10 to 15 mg per kg of body weight per day. This may be taken by your child as a single dose or as divided doses throughout the day. Your doctor will tell you exactly how much medicine your child should take and when to take it.

PACKAGE LEAFLET: INFORMATION FOR THE USER

lsoniazid 100mg Tablets

Children under three months should not take lsoniazid tablets.

Medical check-ups

While you are taking this medicine, your doctor may ask you to have check-ups and blood tests. These are to:

• Check that your liver is working properly. • Make sure your medicine is working properly. • Check the dose you are taking is right for you. If you take more lsoniazid tablets than you should

If you (or someone else) take too many tablets, or you think a child may have swallowed any tablets, contact your nearest hospital casualty department or tell your doctor immediately. Take this leaflet, and any tablets that you still have to show the doctor.

You may experience some of these side effects; slurred speech, high blood sugar, slow breathing, hallucinations, dizziness, fits, or coma.

If you forget to take lsoniazid tablets

If you miss a dose, just carry on with the next one as normal. Do not take a double dose to make up for a forgotten dose.

If you have forgotten several doses tell your doctor when you have your next check-up or blood test. Occasionally people get headache, sleeplessness, excessive dreaming, irritability or nervousness if several doses are missed, or when the treatment is stopped.

If you stop taking lsoniazid tablets

Do not stop taking lsoniazid tablets without first talking to your doctor. It is important you take the full course of this medicine, as directed by your doctor, in order to clear the infection that causes tuberculosis.

If you stop taking this medicine suddenly you may get withdrawal symptoms including a headache, difficulty in sleeping, having more dreams, feeling irritable and feeling nervous.

If you have any further questions on the use of this medicine, ask your doctor or pharmacist.

4. Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them.

If you experience any of the following side effects

contact your doctor as soon as possible:

• Inflammation of the pancreas, which causes severe pain in the abdomen and back (pancreatitis, frequency not known).
• Severe extensive skin damage (separation of the epidermis and superficial mucous membranes) (toxic epidermal necrolysis (TEN), may affect up to 1 in 1,000 people).
• A drug reaction that causes rash, fever, inflammation of internal organs, hematologic abnormalities and systemic illness (DRESS syndrome, may affect up to 1 in 1,000 people). • Yellowing of the skin or whites of the eyes, or urine

getting darker and stools paler, fatigue, weakness, malaise, loss of appetite, nausea or vomiting caused by liver problems (hepatitis, may affect up to 1 in 100 people). Other side effects:

• Convulsions (fits).
• Severe stomach pain.

• Connective tissue disorders such as Lupus syndrome

  which can affect the skin and kidneys (symptoms may include a butterfly-shaped rash over the cheeks and nose, tiredness, a high temperature, feeling or being sick, joint pain and weight loss).

• Mental disturbances including psychotic reactions

  such as hallucinations and delusions.

• Blood disorders which may make you more likely to

  get infections.

• High blood sugar levels, although you may not notice

  any symptoms.

• Inflammation of blood vessels (vasculitis)

  • frequency not known.
  • Acidosis (upset of the acid balance in the body) which may make you feel or be sick, be drowsy or have breath that smells of “pear drops”.
  • Gynaecomastia (increased size of breasts in men).

  • Low levels of vitamin B6 and nutrition problems. This can make you feel irritable, have difficulty sleeping, weak muscles, and cracks at the corner of the mouth or lose weight.

    • Eye problems such as visual disturbances and eye pain. • If you have severe problems with your kidneys, you may get loss of hearing and ringing in your ears. • Tingling or numbness in the hands or feet

      (pins and needles).

    • Constipation.
    • Difficulty in starting to pass urine.
    • Upset stomach and diarrhoea.
    • Fever.
    • Feeling and being sick.
    • Loss of appetite and chills.
    • Dry mouth.
    • Overactive reflexes.
    • Dizziness or feeling if the room is spinning round (vertigo).
    • Red or itchy skin rash or peeling of the skin. Side effects with this medicine are more common in people aged over 35 and in people who break down isoniazid more slowly. The risk of having side effects increases with high doses of lsoniazid tablets. Serious side effects:

    • A red, scaly widespread rash with bumps under the skin and blisters accompanied by fever. The symptoms usually appear at the initiation of treatment (acute generalised exanthematous pustulosis)

      • Frequency not known.

    • Lupus-like syndrome, causing symptoms such as swollen joints, tiredness and rashes

      • Frequency not known.

Reporting of side effects

If you get any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme at: www.mhra.gov.uk/ yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store. By reporting side effects you can help provide more information on the safety of this medicine.

5. How to store lsoniazid tablets

Keep this medicine out of the sight and reach of children. This medicinal product does not require any special storage conditions.

Do not use this medicine after the expiry date which is stated on the carton after EXP. The

expiry date refers to the last day of that

month.

Do not throw away any medicines via

wastewater or household waste. Ask your

pharmacist how to throw away medicines you no longer use. These measures will help protect the environment.

6. Contents of the pack and other information

What lsoniazid tablets contain

• The active substance is isoniazid.

  Each tablet contains 100 mg

  of isoniazid.

• The other ingredients are: calcium

  hydrogen phosphate,

  maize starch (dried), purified talc, colloidal anhydrous silica and magnesium stearate.

What lsoniazid tablets look like and contents of the pack

lsoniazid tablets are white, circular, biconvex uncoated tablets having plain surface on both the sides. lsoniazid tablets are available in blister packs of 7, 10, 14, 20, 28, 30, 56, 60, 84, 90, 100 or 112.

Not all pack sizes may be marketed.

Marketing Authorisation Holder

Morningside Healthcare Ltd.

Unit C, Harcourt Way, Leicester, LE19 1WP, UK Manufacturer

Morningside Pharmaceuticals Ltd.

5 Pavilion Way, Loughborough LE11 5GW, UK Morningside Pharmaceuticals Ltd.

& Aspire Pharma Ltd.

Second Floor, Boss Court

7 Barton Close, Grove Park

Leicester, LE19 1SJ, UK

Aspire Pharma Ltd.

Unit 4, Rotherbrook Court

Bedford Road, Petersfield

GU32 3QG, UK

This leaflet was last revised in September 2025.

MPL15075 - P3.1

PL/PA no: PL 20117.0233

Type: Leaflet

Date of revision: 15.9.25

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