Azathioprine is a type of medicine called an immunosuppressant. Immunosuppressants help to calm or control your body's immune system.
This medicine helps treat inflammatory conditions such as:
- rheumatoid arthritis
- Crohn's disease and ulcerative colitis
- severe inflammation of the liver, skin or arteries
- some blood disorders
If you've had a transplant, taking azathioprine can prevent your body from rejecting your new organ.
Azathioprine is sometimes also used to treat conditions that affect the skin, such as lupus or severe atopic eczema.
Azathioprine is available on prescription only. You'll usually be prescribed this medicine by a specialist doctor.
It comes as tablets. It's also available as an injection, but this is usually only given in hospital.
Who can take azathioprine
Most adults and children can take azathioprine.
You'll have a blood test before you start taking this medicine to make sure it's safe for you.
Who may not be able to take azathioprine
Azathioprine is not suitable for some people. To make sure it's safe for you, tell your doctor before taking this medicine if you:
- have ever had an allergic reaction to azathioprine or any other medicine, including mercaptopurine, a medicine for treating conditions including blood cancer
- have an infection or a high temperature, or generally feel unwell
- have any unusual bleeding or bruising
- have ever had any liver problems
- have ever had cancer
- have a condition that affects your bone marrow
- are due to have surgery involving muscle relaxants
- have Lesch Nyhan syndrome, or a rare inherited condition affecting your NUDT15 gene
- have ever been told that your body produces too little thiopurine methyltransferase (TMT, an enzyme)
- are pregnant or trying to get pregnant
Your dose of azathioprine depends on your body weight and why you need to take it. Your doctor will tell you how much to take.
After a transplant
The usual dose after a transplant is between 1mg and 2.5mg for each kilogram you weigh, taken each day.
You'll usually need to take this medicine long term, probably for the rest of your life.
For other conditions
The usual starting dose is 1mg to 3mg each day, for each kilogram you weigh.
Your doctor may lower your dose as your condition gets better.
However, it takes a while for azathioprine to work. You may have to wait a few months to see an improvement.
How to take it
Swallow the tablets whole, with a drink of water. Do not chew them.
You'll usually take your tablets once or twice a day. You can take them with or without food.
Regular blood tests during treatment
Taking azathioprine can sometimes affect your liver, kidneys or bone marrow.
You'll have blood tests to check your liver function, kidney function and blood count before you start taking this medicine.
From week 1 to week 8 of your treatment you'll have blood tests at least once a week. This is particularly important if you're taking a high dose, or you have kidney or liver problems.
From week 9 onwards you'll have blood tests less often. Your doctor will advise you how often you need them. You may only need them every few months.
It's important to have ongoing monitoring for as long as you're taking azathioprine.
If you forget to take it
Check with your doctor or a pharmacist if you miss 2 doses or more.
If you forget to take 1 dose, take it as soon as you remember, unless it's almost time for the next dose. In this case, skip the missed dose and take the next one at the usual time.
Do not take 2 doses to make up for a missed dose.
If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to help you remember to take your medicine.
If you take too much
- you take more than your prescribed dose of azathioprine, even if you feel well
Go to 111.nhs.uk or call 111
- you take more than your prescribed dose of azathioprine and feel unwell
If you need to go to A&E, do not drive yourself. Get someone else to drive you or call for an ambulance.
Take the medicine packet or leaflet inside it, plus any remaining medicine, with you.
Common side effects
This common side effect of azathioprine happens in more than 1 in 10 people when first starting treatment or when the dose is increased. You'll usually feel better after a week or so. There are things you can do to help cope:
Talk to your doctor if the advice on how to cope does not help and side effects do not go away or they get worse.
Serious side effects
Some people can have serious side effects when taking azathioprine.
Stop taking the medicine and speak to a doctor or contact 111 immediately if:
- you feel tired all the time, dizzy or sick, or you're vomiting or have diarrhoea
- you have a high temperature with shivering or chills, cough or a sore throat
- your joints or muscles are hurting
- your pee changes colour or you start peeing more or less than usual – this can be a sign of kidney problems
- you feel confused, light-headed or weak – these can be signs of low blood pressure
- you're bleeding or bruising more easily than usual
- you notice lumps anywhere on your body
- you have severe stomach ache (abdominal pain) and back pain
Go to 111.nhs.uk or call 111.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to azathioprine.
Taking azathioprine for a long time can increase your chance of getting certain types of cancer, including skin cancer. For this reason, avoid strong sunlight and use a sunscreen (SPF 30 or more), and wear clothes that cover your arms and legs.
Azathioprine can also sometimes affect your liver, kidneys or bone marrow. You'll have regular blood tests while taking it to check for any problems.
Other side effects
These are not all the side effects of azathioprine. For a full list, see the leaflet inside your medicine packet.
Azathioprine and pregnancy
You can take azathioprine during pregnancy.
It's particularly important to continue taking it if you have an autoimmune condition or have had an organ transplant, as you need it to keep you healthy. Do not stop taking your medicine without talking to your doctor.
As azathioprine affects the immune system, it means that after your baby is born, there's a very small risk it can affect the way they fight infections.
If your baby is unwell, speak to a doctor, your midwife or health visitor for advice. It's important to tell them that you took azathioprine during pregnancy.
Azathioprine and breastfeeding
If your doctor, health visitor or midwife says your baby is healthy, you can take azathioprine if you are breastfeeding.
It's important to continue taking azathioprine to keep you well. Breastfeeding will also benefit both you and your baby.
Azathioprine passes into breast milk in tiny amounts. It's been taken by many breastfeeding mothers, and it does not usually cause any side effects in breastfed babies.
As a precaution, if you're taking a high dose of azathioprine, your baby might need some extra blood tests.
Talk to your health visitor, midwife, doctor or pharmacist as soon as possible if you have any concerns about your baby. This includes:
- not feeding as well as usual
- getting frequent infections
Azathioprine and fertility
There's no evidence to suggest that taking azathioprine reduces fertility in either men or women.
However, speak to your doctor if you're trying to get pregnant.
Cautions with other medicines
Azathioprine can affect the way some medicines work. Other medicines can also affect the way azathioprine works.
Tell your doctor or a pharmacist if you:
- take allopurinol, a medicine mainly used for gout
- take ciclosporin or tacrolimus, immunosuppressant medicines
- take warfarin, used to prevent blood clots
- are having chemotherapy, used to treat cancer
- are going to have any type of surgery – tell your doctor or anaesthetist that you take azathioprine beforehand
- have recently had or are due to have any vaccinations, especially a live vaccine, like the Zostavax shingles vaccine for example
Children taking azathioprine must not have a live children's flu vaccine (this usually applies to children aged 2 to 17 years old). Adults are given an inactivated flu vaccine and this usually causes no problems with azathioprine.
Find out more about vaccinations.
Mixing azathioprine with herbal remedies and supplements
There's not enough information to say that complementary medicines, herbal remedies and supplements are safe to take with azathioprine. They're not tested in the same way as pharmacy and prescription medicines. They're generally not tested for the effect they have on other medicines.
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