by Nathan Wei, MD, FACP, FACR
Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.
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From the NIH
Azathioprine has been used since the mid-1960’s to treat rheumatoid arthritis, dermatomyositis, polymyositis, and systemic lupus erythematosus.
Azathioprine is a pill that is sold under the brand name of Imuran (GlaxoSmithKline). Azathioprine is a drug that is converted to an active metabolite. After azathioprine gets into the blood stream, it is changed by the liver to a chemical called “6-mercaptopurine” (also called “6-MP”). 6-MP, which also has been used to treat arthritis, is actually the drug that combats inflammation. Besides treating rheumatoid arthritis and systemic lupus erythematosus, Imuran sometimes is used to treat psoriatic arthritis and inflammatory muscle diseases (for example, polymyositis).
Imuran inhibits the functioning of some cells (lymphocytes) involved in causing inflammation. It is unknown whether this is the primary way that Imuran works or whether some other effect is more important.
Approximately 50-70% of patients who take Imuran for rheumatoid arthritis respond to it. For other forms of arthritis the results are less certain. Imuran generally takes 6-12 weeks to start working. A common starting dose for adults is 50 milligrams (one pill) per day. After 4 to 8 weeks the dose may be increased by 1/2 or 1 pill. Further increases, if necessary, are made monthly. Rheumatologists prescribe the lowest dose that controls the arthritis, but most adults taking Imuran require 1 to 3 pills per day. The daily dose may be taken all at once or divided into two separate doses.
Approximately 20-30% of people taking Imuran for rheumatoid arthritis stop it because of side-effects. The most common adverse effect is a decrease in the blood counts. This is more common with larger doses of the drug. As many as 30% of people experience a slight decrease in blood counts. About 5% have serious decreases. Decreased numbers of white blood cells, platelets, red blood cells or a combination of the three may occur. The blood counts usually return to normal within 3 weeks after stopping the medication and most people are able to restart the Imuran (at a lower dose). However, if the blood counts get low enough, abnormal bleeding or bruising (due to decreased numbers of platelets) or serious infection (due to decreased numbers of white blood cells) can occur. Anemia also is a potential problem. On rare occasions, decreased counts can be life-threatening. Due to this risk, regular blood testing is necessary. Most rheumatologists recommend monthly blood counts (to include red cell, white cell and platelets) while taking Imuran. Testing may be needed every 1 or 2 weeks when the medication is first started or the dose changed.
Since Imuran decreases the body’s immune functioning, serious (potentially fatal) infections can occur—even if the blood counts are normal. Anyone taking Imuran who develops signs of infection (such as fever, chills or sweats) should consult a physician immediately! In addition, vaccinations with live viruses (for example, polio) are not recommended. Vaccinations with killed viruses (for example, flu shots) are not dangerous but may not be as effective for people taking Imuran.
Gastrointestinal side-effects occur commonly with Imuran. Nausea (with or without vomiting) occurs in 10-15% of people taking this medication. This most often happens during the first 3 months and can be minimized by taking the medication after eating. Less often, people get stomach pain or diarrhea.
Imuran may cause a temporary decrease in fertility. In addition, Imuran can cause mutations and damage to an unborn baby. Therefore, pregnancy should not occur while taking Imuran! Most physicians recommend that Imuran be stopped 3 months before trying to have children. Also, Imuran should not be taken if a woman is breast feeding. Temporary abnormalities in the menstrual period can occur in women taking Imuran.
Taking Imuran probably increases the risk of getting future cancers. It is impossible to estimate the magnitude of this increased risk but it is small. Individuals who previously have taken medications such as cyclophosphamide (Cytoxan), increase the cancer risk further.
Rash occurs in about 2% of people taking Imuran. The following side-effects occur in less than 1% of people taking this drug: irritation of the liver, irritation of the pancreas (“pancreatitis”) and fever. The gout medicine allopurinol (sold under the brand name “Zyloprim”) causes a dangerous drug interaction when taken with Imuran. Rarely are the two medications prescribed simultaneously. If Imuran is taken with allopurinol, the dose of the Imuran is reduced to 1/3 or 1/4 the usually prescribed dose. Thus, unless specifically told otherwise by a physician, Imuran and allopurinol (Zyloprim) should not be taken simultaneously!
Since other second line drugs work as well or better than Imuran and are not associated with the increased cancer risk, Imuran is not as often prescribed for rheumatoid arthritis as other second line drugs. Any person taking this medication should be very familiar with the risks and symptoms of side-effects.
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