It is very important that your doctor check the progress of you or your child at regular visits to make sure that this medicine is working properly. Blood tests may be needed to check for unwanted effects. Genetic testing may also be performed to check your levels of thiopurine S-methyltransferase (an enzyme needed to metabolize mercaptopurine).
Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using this medicine, tell your doctor right away.
Do not use this medicine if you or your child are also taking azathioprine (Imuran®). Using these medicines together could cause serious unwanted effects. Also, do not use this medicine if you have been treated with mercaptopurine or thioguanine (Tabloid®) in the past and did not work well.
This medicine may increase your risk of getting certain types of cancer. Some teenagers and young adults with Crohn's disease or ulcerative colitis developed a rare type of cancer called hepatosplenic T-cell lymphoma (HSTCL). Talk with your doctor if you or your child have unusual bleeding, bruising, or weakness; swollen lymph nodes in the neck, underarms, or groin; or unexplained weight loss.
While you are being treated with mercaptopurine, and after you stop treatment with it, do not have any immunizations (vaccines) without your doctor's approval. Mercaptopurine may lower your body's resistance and there is a chance you or your child might get the infection the vaccine is meant to prevent. In addition, other persons living in your household should not take oral polio vaccine since there is a chance they could pass the polio virus on to you. Also, avoid persons who have taken oral polio vaccine. Do not get close to them and do not stay in the same room with them for very long. If you cannot take these precautions, you should consider wearing a protective face mask that covers the nose and mouth.
Mercaptopurine can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:
- If you can, avoid people with infections. Check with your doctor immediately if you think you or your child are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
- Check with your doctor immediately if you or your child notice any unusual bleeding or bruising; black, tarry stools; blood in the urine or stools; or pinpoint red spots on your skin.
- Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
- Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.
- Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
- Avoid contact sports or other situations where bruising or injury could occur.
Do not stop taking this medicine without checking first with your doctor.
Stop using this medicine and check with your doctor right away if you or your child have pain or tenderness in the upper stomach; pale stools; dark urine; loss of appetite; nausea; unusual tiredness or weakness; or yellow eyes or skin. These could be symptoms of a serious liver problem.
Tell the doctor in charge that you are taking this medicine before you have any medical tests. The results of tests for the amount of sugar or uric acid in the blood measured by a machine called a sequential multiple analyzer (SMA) may be affected by this medicine.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.