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Active substance: ISONIAZID

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Patient Information Leaflet:
Isoniazid 50 mg &100 mg Tablets BP Isoniazid

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Read all of this leaflet carefully before you start
taking this medicine.
• Keep this leaflet. You may need to read it again
• If you have any further questions, ask your doctor
or pharmacist
• This medicine has been prescribed for you. Do
not pass it on to others. It may harm them, even if
their symptoms are the same as yours
• In this leaflet, Isoniazid 50 mg & 100 mg Tablets
BP are called Isoniazid.
In this leaflet:
1. What Isoniazid is for
2. Before you take Isoniazid
3. How to take Isoniazid
4. Possible side effects
5. How to store Isoniazid
6. Further information.


1. What Isoniazid is for
Isoniazid belongs to a group of medicines called
antibacterials. Isoniazid works by killing bacteria
that cause tuberculosis (also known as TB).
Isoniazid is used to treat tuberculosis inside the lungs
(pulmonary TB) and outside the lungs (extrapulmonary TB)
Tuberculosis is a serious infectious disease that can
be passed on to other people. If left untreated it can
spread through your body and may be fatal. It is
important that you receive effective treatment for
this condition.
2. Before you take Isoniazid
Do not take Isoniazid if:
• You are allergic to Isoniazid or any of the other
ingredients of Isoniazid (see Section 6)
• You have ever had serious liver problems after
taking any medicine.
If any of the above applies to you, talk to your
doctor or pharmacist.
Check with your doctor before taking Isoniazid if:
• You have epilepsy or have ever had convulsions
• You have diabetes
• You drink a lot of alcohol regularly

• You have, or have had, problems with your liver
or kidneys.
• You suffer or have suffered from psychosis (mental
disturbances with hallucinations or delusions)
• You are malnourished (severely underfed)
• You have HIV infection
• You have extra-pulmonary TB (outside the lungs)
Tell your doctor if you are taking any of the
following medicines:
• Stavudine (used for the treatment of HIV)
• Any medicine for the treatment of epilepsy such as
carbamazepine, phenytoin or primadone
• Disulfiram (for the treatment of alcoholism)
• Rifampicin, paraminosalicyclic acid or any other
drug used to treat TB
• The benzodiazepine diazepam (for the treatment
of anxiety)
• Levodopa (for the treatment of Parkinson's
• Itraconazole or ketaconazole (for the treatment of
fungal infections)
• Any other medicine, including medicines obtained
without a prescription.
These medicines can interfere with how well your
treatment works.

Taking Isoniazid with food and drink
Isoniazid should be taken on an empty stomach, so
take it at least 30 minutes before a meal or two
hours after a meal. This helps your body absorb
Isoniazid more easily. Avoid drinking alcohol with
Isoniazid. This may damage your liver. Isoniazid
may interact with foods containing histamine (e.g.
tuna fish) or tyramine (e.g. cheese, red wine). These
foods should be avoided if you are receiving
Pregnancy and breast-feeding
If you are pregnant, trying to become pregnant or
breast-feeding, ask your doctor or pharmacist for
advice before taking Isoniazid.
Warning about sugar in Isoniazid
This product contains a sugar (lactose). If you have
been told that you are intolerant to some sugars,
contact your doctor before taking this medicine.
3. How to take Isoniazid
Always take Isoniazid exactly as your doctor has
told you.
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
Remember: Isoniazid should not be taken with
food. You should swallow Isoniazid tablets whole
with a glass of water.
The usual dose of Isoniazid 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).
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 of 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.
Children under three months should not take
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 Isoniazid than you should
Do not take more Isoniazid than you should. If you
accidentally take too much, immediately contact the
nearest hospital casualty department or your doctor.
Taking too much Isoniazid may cause; feeling and
being sick, dizziness or feeling if the room is spinning
round, fits and acidosis (upset of the acid balance in
the body). These effects may require emergency
treatment in hospital.

If you forget to take Isoniazid
Do not take a double dose to make up for a missed
dose. Simply take the next dose as planned.

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If you stop taking Isoniazid
Do not stop taking Isoniazid 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 about the use of this
medicine, ask your doctor or pharmacist.
4. Possible side-effects
Like all medicines Isoniazid 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, cracks at the corner of the
mouth or lose weight
• Eye problems such as visual disturbances and eye
• 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
• 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
• 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 Isoniazid.
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 Yellow Card Scheme on the MHRA
website ( By reporting
side effects you can help provide more information on
the safety of this medicine.
5. How to store Isoniazid
Keep out of the reach and sight of children.
Do not use Isoniazid after the expiry date on the pack.
The expiry date refers to the last day of that month.
Store below 25ºC.
Medicines should not be disposed of via wastewater
or household waste. Return any medicine you no
longer need to your pharmacist.
6. Further information
What Isoniazid contains
• The active substance in Isoniazid Tablets BP is
• Isoniazid tablets come in two strengths: 50 mg and
100 mg. Each 50 mg tablet contains 50 mg

isoniazid. Each 100 mg tablet contains 100 mg
The other ingredients in Isoniazid are lactose 170
mesh, maize starch, microcrystalline cellulose, alginic
acid (E400), magnesium stearate and purified water.

This leaflet was last updated August 2015.
If this leaflet is difficult to see or read, or you would
like it in a different format, please contact
RPH Pharmaceuticals AB, Lagervägen 7,
136 50 Haninge, Sweden.

What Isoniazid looks like and contents of the pack
Isoniazid tablets are round, white, uncoated tablets.
The 50 mg tablets are embossed with “50 151” on
one side and “EVANS” on the other.
The 100 mg tablets are embossed with “100 152” on
one side and “EVANS” on the other.
Isoniazid 50 mg and 100 mg tablets come in a
coloured plastic container with a lid. Containers may
contain 7, 14, 21, 28, 30, 50, 56, 60, 84, 90, 100,
112, 120 or 250 tablets. Not all pack sizes may be
Marketing Authorisation Holder:
RPH Pharmaceuticals AB, Lagervägen 7, 136 50
Haninge, Sweden.
Recipharm Ltd., Vale of Bardsley, Ashton under Lyne,
Lancashire, OL7 9RR, UK.
Distributed by Focus Pharmaceuticals Ltd.


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Source: Medicines and Healthcare Products Regulatory Agency

Disclaimer: Every effort has been made to ensure that the information provided here is accurate, up-to-date and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. This information has been compiled for use by healthcare practitioners and consumers in the United States. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate that the drug or combination is safe, effective or appropriate for any given patient. If you have questions about the substances you are taking, check with your doctor, nurse or pharmacist.