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Drug Class – Antimetabolite

Mechanism of Action

Drugs of this class alter RNA and DNA, building blocks of all cells, resulting in blunting of the immune system.

Diseases Treated With this Medication

This medication is primarily used to prevent kidney transplant rejection and to treat severe rheumatoid arthritis. Other kidney diseases treated with this medication, although not FDA approved indications, include lupus nephritis and systemic vasculitis. It is also used to treat autoimmune diseases although not FDA approved including idiopathic thrombocytopenic purpura, autoimmune hemolytic anemia, multiple sclerosis, and Crohn’s disease.

Common Side Effects

  • Nausea and vomiting
  • Decreased white blood cell count (leukopenia). You may be tested for thiopurine methyltransferase deficiency (TMPT deficiency) as this deficiency poses a greater risk for decreased white blood cell count.
  • Decreased red blood cell count (anemia)

Other Serious Side Effects

  • Liver toxicity
  • Decreased platelet count (thrombocytopenia)
  • Increased risk of infections
  • Cancer

Drug Interactions

Drug Name


Angiotensin Converting Enzyme Inhibitors (ACE-I) eg. lisinopril, enalapril

May increase risk of decreased red blood cell count (anemia) and white blood cell count (leukopenia)

Allopurinol (Zyloprim®)

May increase azathioprine levels and increase side effects

Cyclosporine (Neoral®, Sandimmune®, Gengraff®)

Azathioprine may decrease cyclosporine concentrations in the blood

Febuxostat (Uloric®)

May increase azathioprine levels and increase side effects

Patient Instructions

  • Tell all dentists, surgeons, and other doctors that you use this drug.
  • While taking azathioprine you may have more chance of getting an infection. Wash hands often. Stay away from people with infections, colds, or flu.
  • While taking azathioprine you have an increased chance of skin cancer. Avoid sun, sunlamps, and tanning beds. Use sunscreen and wear clothing and eyewear that protects you from the sun.
  • Tell your doctor if you are pregnant or plan on getting pregnant. You will need to talk about the benefits and risks of using this drug while you are pregnant.
  • If you forget to take your medicine or miss a dose, take it as soon as possible. If it is close to the time for your next dose, skip the missed dose and take the medicine on schedule. Do not take extra medicine to make up for missed doses.
  • This medicine should be stored in a tightly closed container at room temperature, and away from heat, moisture and direct light.