What is azathioprine, and how does it work (mechanism of action)?
Azathioprine is an
immunosuppressant, that is, a drug that is used to suppress the immune system.
It is used to treat patients who have undergone kidney transplantation and for
diseases in which modifying the activity of the immune system is important.
Azathioprine is a prodrug (a precursor of a drug) which is converted in the body
to its active form called mercaptopurine (Purinethol). The exact mechanism of
action of azathioprine is not known.
Like other immunosuppressants, it suppresses the proliferation of T and B
lymphocytes, types of white blood cells that are part of the immune system and
defend the body against both infectious diseases and foreign materials. For
example, in the case of organ transplantation, immunosuppressants prevent the
body from immunologically rejecting the new organ. In the case of autoimmune
diseases (diseases caused by an abnormal immune reaction against the body’s own
tissues) such as rheumatoid
arthritis, suppressing the immune system reduces the inflammation that
accompanies immune reactions and slows damage to the joints caused by the
inflammation. The FDA approved azathioprine in March 1968.
What brand names are available for azathioprine?
Imuran, Azasan
Is azathioprine available as a generic drug?
Yes
Do I need a prescription for azathioprine?
Yes
What are the side effects of azathioprine?
The most common serious side effects of
azathioprine involve the cells of the blood and gastrointestinal system.
Azathioprine can cause serious lowering of the white blood cell count, resulting
in an increased risk of infections. This effect is reversed when the dose of
azathioprine is reduced or temporarily discontinued. Azathioprine can cause
nausea,
vomiting,
and loss of appetite, which may resolve when the daily dose is reduced or
divided and taken more than once a day. Azathioprine can cause liver toxicity
(for example, in less than 1% of rheumatoid arthritis patients). All patients
taking azathioprine require regular testing of blood for blood cell counts and
liver tests to monitor for side effects of azathioprine. Other side effects
encountered less frequently include fatigue,
hair loss, joint
pains, and diarrhea.
What is the dosage for azathioprine?
The initial dose for preventing organ rejection is 3
to 5 mg/kg (oral or IV) daily, starting at the time of transplantation or in
some cases 1 to 3 days before transplantation. The initial off-label dose for
treating rheumatoid arthritis is 1.0 mg/kg (50 to 100 mg, oral or IV) as a
single dose or twice daily. Doses may be increased by 0.5 mg/kg daily up to a
maximum dose of 2.5 mg/kg per day. Dosing for other off-label use may vary
according to what disease is being treated; in general, off-label use should be
done by an experienced medical specialist. Azathioprine should be taken with
food.
Which drugs or supplements interact with azathioprine?
Allopurinol
(Zyloprim) that is used for treating increased blood levels of uric acid and
preventing
gout increases azathioprine levels in the blood which may increase the risk
of side effects from azathioprine. Therefore, it is important to reduce the dose
of azathioprine by approximately 1/3 to 1/4 in patients taking allopurinol. The
use of
angiotensin-converting enzyme (ACE) inhibitors to control
high blood pressure in patients taking azathioprine has been reported to
induce anemia (low
levels of red blood cells) and severe leukopenia (low levels of white blood
cells). Azathioprine reduces blood levels of the blood thinner,
warfarin
(Coumadin), and thus may reduce the blood thinning effect of warfarin.
Is azathioprine safe to take if I’m pregnant or breastfeeding?
Azathioprine can cause fetal harm when given to
pregnant women
and whenever possible should be avoided.
Azathioprine is found in
breast milk
and should not be used in nursing mothers.
What else should I know about azathioprine?
What preparations of azathioprine are available?
Tablet: 25, 50, 75, 100 mg. Injection: 100 mg
How should I keep azathioprine stored?
Azathioprine should be stored at 15 C -25 C (59 F
-77 F) in a dry place and protected from light.