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What is azathioprine and why is it prescribed?

Azathioprine (trade name: Imuran) is a disease-modifying anti-rheumatic drug (DMARD). It reduces the activity of the body's defence mechanism (immune system), which may be overactive in some conditions.

Azathioprine modifies the underlying disease process to limit or prevent tissue damage and disability, rather than having an immediate effect on symptoms. It's a long-term treatment, so it may be 6-12 weeks before you start to notice the benefits.

Unless you have severe side-effects it's important to keep taking azathioprine:

  • even if it doesn't seem to be working at first
  • even when your symptoms improve (as this will help to keep the disease under control).

Azatioprine is usually initiated by a specialist for people with:

Your doctor may also prescribe azathioprine if you're on steroid treatment so that your steroid dose can be reduced.

Azathioprine may need to be used with caution, in reduced doses if:

  • you have severe liver or kidney problems
  • you have bone marrow problems.

If you're on other medications which could interact with azathioprine (e.g. allopurinol, warfarin) then your doctor may suggest another treatment or a different dose either of the azathioprine or of your other medication.

Before prescribing azathioprine, your doctor may order a blood test for an enzyme called TPMT (thiopurine s-methyltransferase). This enzyme helps to break down and remove azathioprine from the body. Low levels of TPMT may mean there is a little more risk of side-effects from azathioprine, so your doctor may suggest a lower dose than usual.

If the result is very low, azathioprine may not be the right medication for you, and your doctor will discuss other treatments with you.

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