Azathioprine (Imuran is the commercial name) and 6-Mercaptopurine (better known a 6-MP) are used in kidney transplants to weaken the immune system so that the new kidney can be accepted and work properly. As a result, these medicines are considered immune suppressants or immunomodulators, because they suppress or weaken the immune system when that's necessary. For example, they work in auto-immune disorders like rheumatoid arthritis, where the immune system is attacking the joints. In the same way, they have been used in IBD since the 1960s to lessen the immune system's impact on the intestine.

It's been estimated that 25% of those with ulcerative colitis (UC) are taking one of these 2 medicines (grouped together as thiopurines). In both Crohn's disease and UC, they are effective medicines for ongoing (maintenance) treatment. They are able to cut down or eliminate the need for steroids. And they are sometimes used along with other medicines to increase the effect of the other medicines.

Studies have shown that as many as 53-94% of patients are able to be in clinical remission a year after they start taking these medicines. However, the studies showing these positive effects were all done on small groups or in the early days, when comparison groups and the meaning of remission weren't clearly established.  In addition, the fact that these medicines have been used for a long time has allowed us to see serious side effects can develop for some.

Starting Out

These medicines are prescribed based on a person's weight and their ability to break down (metabolize) and eliminate the medicine from their bodies. 85% of people have the enzymes they need so they can take a full dose of the medicine. But 4% of people shouldn't take these medicines at all because their enzymes are lacking. Another 11% of people have a medium amount of the enzymes and their dose usually can be adjusted. Fortunately, there is a gene test available that can tell how much of the enzyme someone has, so the dosing will be right for each person.

While waiting for the gene test to come back, patients can check with their doctors to make sure their vaccines are up to date and to test for any infections that the patient might not know they have. Some doctors will recommend testing for TB and / or hepatitis. If these are present, the doctor may treat them first before starting one of the thiopurines.

If the gene and infectious tests are fine, about 75% of patients respond to the medication and stay on it. Patients may start on steroids at the same time or still be on steroids, because it can take up to 3 months of treatment for these medicines to have their full effect. But that also means that 25% usually stop the medicine within the first 3 months. Those patients don't tolerate the medicine because of one of the early side effects that can show up.

Blood tests can be done later to monitor the medicine to make sure the dose is in a range where it will have the most effect and least chance of side effects.

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