AZATHIOPRINE II: Side Effects
There are several notable side effects of the thiopurines [azathioprine (AZA)/ 6-mercaptopurine (6-MP)]. They can be classified as early or late onset.
The early reactions are allergic and affect about 5% of users. They include pancreatitis (inflammation of the pancreas), hepatitis (inflammation of the liver), fever, nausea, rash, and fatigue. Abrupt discontinuation of medication leads to complete resolution of symptoms.
Late onset, or dose dependent, reactions include decreased levels of white blood cells (leukopenia), red blood cells (anemia), and platelets (thrombocytopenia) due to suppression of the bone marrow and hepatitis. It is not clear if thiopurines increase the risk of lymphomas or other cancers. Several studies have produced conflicting results. Leukopenia causes an increased risk of infections and thrombocytopenia causes bruising and bleeding.
In order to minimize the risk of dose-dependent side effects, blood tests are performed regularly on patients using AZA/6-MP to evaluate bone marrow suppression and hepatitis. White blood cell count and liver enzymes are tested every 2-4 weeks during the first couple months of therapy and after dose increases, but once a steady dose is achieved testing is performed approximately every three months. If testing shows an abnormality then either the dosing is adjusted or the medicine is changed.
If the thiopurines are used appropriately and followed closely then they are very safe and effective medications for moderate to severe UC, but they cannot be safely taken without follow-up. Skipping blood tests can lead to life threatening complications.