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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
• 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 (extra-pulmonary 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
• 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 (fits)
• 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
• You are malnourished (severely underfed)
• You have HIV infection
• You have extra-pulmonary TB (outside the
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
• 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 isoniazid.

Pregnancy and breast-feeding
If you are pregnant, trying to become
pregnant or breast-feeding, ask your doctor
or pharmacist for advice before taking
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 pharmacist.
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
The usual dose is 5 to 10 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.
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

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• Make sure your medicine is working
• Check the dose you are taking is right for
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
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

4. Possible side-effects
Like all medicines Isoniazid can cause side
effects, although not everybody gets them.
Stop taking Isoniazid and get immediate
medical help if you have any of the following
• Yellowing of your skin or the whites of your
eyes (jaundice)
• Feeling or being sick
• Loss of appetite
• Tiredness
• Weakness.
You may be developing a serious problem with
your liver.
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
• Blood disorders which may make you more
likely to get infections
• High blood sugar levels, although you may
not notice any symptoms
• 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
• 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 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 Isoniazid.
If any of these side effects gets serious, or if you
notice any side effects not listed in this leaflet,
please tell your doctor or pharmacist

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

6. Further information
What Isoniazid contains
• The active substance in Isoniazid Tablets BP
is isoniazid.
• 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 isoniazid.
The other ingredients in Isoniazid are lactose
170 mesh, maize starch, microcrystalline
cellulose, alginic acid (E400), magnesium
stearate and purified water.
What Isoniazid looks like
Isoniazid tablets are white oval-shaped 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 marketed.
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.
This leaflet was last updated October 2011.

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.

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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.