What are immunomodulator medications?
Immunomodulators are medications that weaken the body's immune system. The immune system is composed of immune cells and the proteins that these cells produce. These cells and proteins serve to defend the body against harmful bacteria, viruses, fungi, and other foreign invaders. Activation of the immune system causes inflammation within the tissues where the activation occurs. (Inflammation is, in fact, an important mechanism to defend the body used by the immune system.) Normally, the immune system is activated only when the body is exposed to harmful invaders. In patients with Crohn's disease and ulcerative colitis, however, the immune system is abnormally and chronically activated in the absence of any known invader. Immunomodulators decrease tissue inflammation by reducing the population of immune cells and/or by interfering with their production of proteins that promote immune activation and inflammation. Generally, the benefits of controlling moderate to severe ulcerative colitis outweigh the risks of infection due to weakened immunity. Examples of immunomodulators include azathioprine (Imuran), 6-mercaptopurine (6-MP, Purinethol), cyclosporine (Sandimmune), and methotrexate (Rheumatrex, Trexall).
Azathioprine (Imuran) and 6-MP (Purinethol)
Azathioprine and 6-mercaptopurine (6-MP) are medications that weaken the body's immunity by reducing the population of a class of immune cells called lymphocytes. Azathioprine and 6-MP are related chemically. Specifically, azathioprine is converted into 6-MP inside the body. In high doses, these two drugs have been useful in preventing the rejection of transplanted organs and in treating leukemia. In low doses, they have been used for many years to treat patients with moderate to severe Crohn's disease and ulcerative colitis.
Azathioprine and 6-MP are increasingly recognized by doctors as valuable drugs in treating Crohn's disease and ulcerative colitis. Some 70% of patients with moderate to severe disease will benefit from these drugs. Because of the slow onset of action and the potential for side effects, however, 6-MP and azathioprine are used mainly in the following situations:
- Patients with ulcerative colitis and Crohn's disease not responding to corticosteroids.
- Patients who are experiencing undesirable corticosteroid-related side effects.
- Patients who are dependent on corticosteroids and are unable to discontinue them without developing relapses.
When azathioprine and 6-MP are added to corticosteroids in the treatment of ulcerative colitis patients who do not respond to corticosteroids alone, there may be an improved response or smaller doses and shorter courses of corticosteroids may be effective. Some patients can discontinue corticosteroids altogether without experiencing relapses. The ability to reduce corticosteroid requirements has earned 6-MP and azathioprine their reputation as "steroid-sparing" medications.
In patients with severe ulcerative colitis who suffer frequent relapses, 5-ASA may not be sufficient, and more potent azathioprine and 6-MP will be necessary to maintain remissions. In the doses used for treating ulcerative colitis and Crohn's disease, the long-term side effects of azathioprine and 6-MP are less serious than long-term oral corticosteroids or repeated courses of oral corticosteroids.
What Are the Side Effects of 6-MP and Azathioprine?
Side effects of 6-MP and azathioprine include increased vulnerability to infections, inflammation of the liver (hepatitis) and pancreas, (pancreatitis), and bone marrow toxicity (interfering with the formation of cells that circulate in the blood).
The goal of treatment with 6-MP and azathioprine is to weaken the body's immune system in order to decrease the intensity of inflammation in the intestines; however, weakening the immune system increases the patient's vulnerability to infections. For example, in a group of patients with severe Crohn's disease unresponsive to standard doses of azathioprine, raising the dose of azathioprine helped to control the disease, but two patients developed cytomegalovirus (CMV) infection. CMV usually infects individuals with weakened immune systems such as patients with AIDS or cancer, especially if they are receiving chemotherapy, which further weakens the immune system.
Azathioprine and 6-MP-induced inflammation of the liver (hepatitis) and pancreas (pancreatitis) are rare. Pancreatitis typically causes severe abdominal pain and sometimes vomiting. Pancreatitis due to 6-MP or azathioprine occurs in a small percentage of patients, usually during the first several weeks of treatment. Patients who develop pancreatitis should not receive either of these two medications again.
Azathioprine and 6-MP also suppress the bone marrow. The bone marrow is where red blood cells, white blood cells, and platelets are made. Actually, a slight reduction in the white blood cell count during treatment is desirable since it indicates that the dose of 6-MP or azathioprine is high enough to have an effect; however, excessively low red or white blood cell counts indicates bone marrow toxicity. Therefore, patients on 6-MP and azathioprine should have periodic blood counts (usually every two weeks initially and then every 3 months during maintenance) to monitor the effect of the drugs on their bone marrow.
6-MP can reduce the sperm count in men. When the partners of male patients on 6-MP conceive, there is a higher incidence of miscarriages and vaginal bleeding. There also are respiratory difficulties in the newborn. Therefore, it is recommended that whenever feasible, male patients should stop 6-MP and azathioprine for three months before attempting to conceive.
Patients on long-term, high dose azathioprine to prevent rejection of the kidney after kidney transplantation have an increased risk of developing lymphoma, a malignant disease of lymphatic cells. There is no evidence at present that long term use of azathioprine and 6-MP in the low doses used in IBD increases the risk for lymphoma, leukemia or other malignancies.
Other Issues in the Use of 6-MP
One problem with 6-MP and azathioprine is their slow onset of action. Typically, full benefit of these drugs is not realized for three months or longer. During this time, corticosteroids frequently have to be maintained at high levels to control inflammation.
The reason for this slow onset of action is partly due to the way doctors prescribe 6-MP. Typically, 6-MP is started at a dose of 50 mg daily. The blood count is then checked two weeks later. If the white blood cell count (specifically the lymphocyte count) is not reduced, the dose is increased. This cautious, stepwise approach helps prevent severe bone marrow and liver toxicity, but also delays benefit from the drug.
Studies have shown that giving higher doses of 6-MP early can speed up the benefit of 6-MP without increased toxicity in most patients, but some patients do develop severe bone marrow toxicity. Therefore, the dose of 6-MP has to be individualized. Scientists now believe that an individual's vulnerability to 6-MP toxicity is genetically inherited. Blood tests can be performed to identify those individuals with increased vulnerability to 6-MP toxicity. In these individuals, lower initial doses can be used. Blood tests can also be performed to measure the levels of certain by-products of 6-MP. The levels of these by-products in the blood help doctors more quickly determine whether the dose of 6-MP is right for the patient.
TPMT genetics and safety of azathioprine and 6-MP
Azathioprine is converted into 6-MP in the body, and 6-MP then is partially converted into other chemicals by an enzyme called thiopurine methyltransferase (TPMT). These chemicals then are eliminated from the body. The activity of TPMT that determines the ability to convert 6-MP into other chemicals is genetically determined, and approximately 10% of the population in the United States has reduced or absent TPMT activity. In this 10% of patients, 6-MP and another related chemical (6-thioguanine or 6-TG) accumulate and are toxic to the bone marrow where blood cells are produced. Thus, when given normal doses of azathioprine or 6-MP, these patients with reduced or absent TPMT activity can develop seriously low white blood cell counts for prolonged periods of time, exposing them to serious life-threatening infections.
The Food and Drug Administration now recommends that doctors check TPMT levels prior to starting treatment with azathioprine or 6-MP. Patients found to have genes associated with reduced or absent TPMT activity are treated with alternative medications or are prescribed substantially lower than normal doses of 6-MP or azathioprine.
A word of caution is in order, however. Having normal TPMT genes is no guarantee against azathioprine or 6-MP toxicity. Rarely, a patient with normal TPMT genes can develop severe toxicity in the bone marrow and a low white blood cell count even with normal doses of 6-MP or azathioprine. In addition, with normal levels of TPMT activity, liver toxicity, another toxic effect of 6-MP, can still occur. Therefore, all patients taking 6-MP or azathioprine (regardless of TPMT genetics) have to be closely monitored by a doctor who will order periodic blood counts, and liver enzyme tests for as long as the medication is taken.
Another cautionary note: allopurinol (Zyloprim), used in treating high blood uric acids levels and gout, can induce bone marrow toxicity when used together with azathioprine or 6-MP. This occurs because allopurinol reduces TMPT activity. The combination of genetically-reduced TMPT activity and further reduction of TMPT activity by the allopurinol increases greatly the risk of bone marrow toxicity.
6-MP metabolite levels
In addition to monitoring blood cell counts and liver tests, doctors also may measure blood levels of the chemicals that are formed from 6-MP (6-MP metabolites), which can be helpful in several situations such as:
- If a patient's disease is not responding to standard doses of 6-MP or azathioprine and his/her 6-MP blood metabolite levels are low, compliance should be checked, and if satisfactory, the dose of 6-MP or azathioprine may be increased.
- If a patient's disease does not respond to treatment and his/her 6-MP blood metabolite levels are very low, it is most likely that he/she is not taking his/her medication. The lack of response in this case is due to patient non-compliance.
How Long Can Patients Continue on 6-MP?
Patients have been maintained on 6-MP or azathioprine for years without any important long-term side effects. Their doctors, however, should closely monitor their patients on long-term 6-MP. There is data suggesting that patients on long-term maintenance with 6-MP or azathioprine fare better than those who stop these medications. Those who stop 6-MP or azathioprine are more likely to experience relapses, more likely to need corticosteroids or undergo surgery.
Methotrexate (Rheumatrex, Trexall) is an immunomodulator and anti-inflammatory medication. Methotrexate has been used for many years in the treatment of severe rheumatoid arthritis and psoriasis. It has been helpful in treating patients with moderate to severe Crohn's disease who are either not responding to 6-MP and azathioprine or are intolerant of these two medications. Methotrexate also may be effective in patients with moderate to severe ulcerative colitis who are not responding to corticosteroids or 6-MP and azathioprine. It can be given orally or by weekly injections under the skin or into the muscles. It is more reliably absorbed with the injections.
One major complication of methotrexate is the development of liver cirrhosis when the medication is given over a prolonged period of time (years). The risk of liver damage is higher in patients who also abuse alcohol or have morbid (severe) obesity. Generally, periodic liver biopsies are recommended for a patient who has received a cumulative (total) methotrexate dose of 1.5 grams and higher.
Other side effects of methotrexate include low white blood cell counts and inflammation of the lungs.
Methotrexate should not be used in pregnancy.
Cyclosporine (Sandimmune) is a potent immunosuppressant used in preventing organ rejection after transplantation, for example, of the liver. It also has been used to treat patients with severe ulcerative colitis and Crohn's disease. Because of the approval of infliximab (Remicade) for treating severe Crohn's disease, cyclosporine probably will be used primarily in severe ulcerative colitis. Cyclosporine is useful in fulminant ulcerative colitis and in severely ill patients who are not responding to systemic corticosteroids. Administered intravenously, cyclosporine can be very effective in rapidly controlling severe colitis and avoiding or delaying surgery.
Cyclosporine also is available as an oral medication, but the relapse rate with oral cyclosporine is high. Therefore, cyclosporine seems most useful when administered intravenously in acute situations.
Side effects of cyclosporine include high blood pressure, impairment of kidney function, and tingling sensations in the extremities. More serious side effects include anaphylactic shock and seizures.
Infliximab (Remicade) is an antibody that attaches to a protein called tumor necrosis factor-alpha (TNF-alpha). TNF-alpha is one of the proteins produced by immune cells during activation of the immune system. TNF-alpha, in turn, stimulates other cells of the immune system to produce and release other proteins that promote inflammation. In Crohn's disease and in ulcerative colitis, there is continued production of TNF-alpha as part of the immune activation. Infliximab, by attaching to TNF-alpha, blocks its activity and in so doing decreases the inflammation.
Infliximab, an antibody to TNF-alpha, is produced by the immune system of mice after the mice are injected with human TNF-alpha. The mouse antibody then is modified to make it look more like a human antibody, and this modified antibody is infliximab. Such modifications are necessary to decrease the likelihood of allergic reactions when the antibody is administered to humans. Infliximab is given by intravenous infusion over two hours. Patients are monitored throughout the infusion for side effects.
Infliximab has been used effectively for many years for the treatment of moderate to severe Crohn's disease that was not responding to corticosteroids or immuno-modulators. In Crohn's disease patients, a majority experienced improvement in their disease after one infusion of infliximab. Some patients noticed improvement in symptoms within days of the infusion. Most patients experienced improvement within two weeks. In patients who respond to infliximab, the improvements in symptoms can be dramatic. Moreover, there can be impressively rapid healing of the ulcers and the inflammation in the intestines after just one infusion.
Only over the last few years infliximab also has been used to treat severe UCs. In a study of over 700 patients with moderate to severe UC, for example, infliximab was found to be more effective than placebo in inducing and maintaining remission.
Infliximab is typically given to induce remission in three doses - at time zero and then two weeks and four weeks later. After remission is attained, maintenance doses can be given every other month.
Side effects of infliximab
Infliximab, generally, is well tolerated. There have been rare reports of side effects during infusions, including chest pain, shortness of breath, and nausea. These effects usually resolve spontaneously within minutes if the infusion is stopped. Other commonly reported side effects include headache and upper respiratory tract infection.
Infliximab, like immuno-modulators, increases the risk for infection. One case of salmonella colitis and several cases of pneumonia have been reported with the use of infliximab. There also have been cases of tuberculosis (TB) reported after the use of infliximab.
Because infliximab is partly a mouse protein, it may induce an immune reaction when given to humans, especially with repeated infusions. In addition to the side effects that occur while the infusion is being given, patients also may develop a "delayed allergic reaction" that occurs 7-10 days after receiving the infliximab. This type of reaction may cause flu-like symptoms with fever, joint pain and swelling, and a worsening of Crohn's disease symptoms. It can be serious, and if it occurs, a physician should be contacted. Paradoxically, those patients who have more frequent infusions of Remicade are less likely to develop this type of delayed reaction compared to those patients who receive infusions separated by long intervals (6-12 months).
There are some reports of worsening heart disease in patients who have received Remicade. The precise mechanism and role of infliximab in the development of this side effect is unclear. As a precaution, individuals with heart disease should inform their physician of this condition before receiving infliximab.
There have been rare reports of nerve damage such as optic neuritis (inflammation of the nerve of the eye) and motor neuropathy (damage to the nerves controlling muscles).
There have also been rare reports of patients developing viral colitis (cytomegalovirus and herpes simplex virus) while on immunosuppressive medications. These viral infections can mimic a flare of ulcerative colitis and mistakenly suggest resistance to therapy. Before increasing the dose or changing the medication being used to treat the ulcerative colitis, patients should have a thorough evaluation including flexible sigmoidoscopy or limited colonoscopy with biopsies to help make the diagnosis of viral colitis.
Precautions with infliximab
Infliximab can aggravate and cause the spread of an existing infection. Therefore, it should not be given to patients with pneumonia, urinary tract infection or abscess (localized collection of pus).
It now is recommended that patients be tested for TB prior to receiving infliximab. Patients who previously had TB should inform their physician of this before they receive infliximab.
Infliximab can cause the spread of cancer cells; therefore, it should not be given to patients with cancer.
The effects of infliximab on the fetus are not known although the literature suggests that this medication is safe for women to continue until week 32 of pregnancy. At that time, the risk of exposure of the fetus to this medication by placental transfer is increased. Infliximab is listed as a pregnancy category B drug by the FDA (meaning there has been no documented human toxicity).
Because infliximab is partly a mouse protein, some patients can develop antibodies against infliximab with repeated infusions. The development of these antibodies can decrease the effectiveness of the drug. The chances of developing these antibodies can be decreased by concomitant use of 6-MP and corticosteroids. There are ongoing studies in patients who have lost their initial response to infliximab to determine whether measurement of antibody titers will be helpful in guiding further treatment. Results of these studies are not yet available.
While infliximab represents an exciting new class of medications in the fight against Crohn's disease and ulcerative colitis, caution is warranted because of potentially serious side effects. Doctors are using infliximab in moderate to severe ulcerative colitis not responding to other medications.
Other biological therapies under development
Adalimumab is an anti-TNF drug similar to infliximab. It decreases inflammation by blocking tumor necrosis factor (TNF-alpha). In contrast to infliximab, adalimumab is a fully humanized anti-TNF antibody containing no mouse protein and, therefore, might cause less of an immune reaction. Adalimumab is administered subcutaneously (under the skin) instead of intravenously as in the case of infliximab.
Rheumatologists have been using adalimumab for treating inflammation of the joints in patients with rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis. It was also approved by the FDA in 2007 for the treatment of moderately to severely active Crohn's disease. Though not approved formally by the FDA for treatment of ulcerative colitis, a few studies have shown it to have some efficacy in treating patients with ulcerative colitis who are refractory to or have lost their response to infliximab. More information will be required before recommending this as a standard therapy.
Visilizumab (anti-CD3 antibody)
Visilizumab is a humanized antibody that specifically binds to human CD3 expressing T cells, that inhibits the activity of the cells. (CD3 expressing T cells are part of the immune system and seem to play an important role in promoting the inflammation of ulcerative colitis.). In a phase 1 open-label study evaluating the safety and tolerability of this medication, 32 subjects received visilizumab. Results showed that 84% of these patients achieved a clinical response by day 30, 41% achieved clinical remission, and 44% achieved endoscopic remission. The main side effects were decreased CD4 counts and cytokine release syndromes (flu-like symptoms, etc.), though there were no serious infections. Initial data seems promising though more must be learned about this medication before it can be used routinely. This medication is not yet approved by the FDA for the treatment of ulcerative colitis.
Alpha-4 integrin blockade
Alpha-4 integrins on the surface of cells of the immune system help the cells to leave the blood and travel into the tissues where they promote inflammation. Antibodies against these integrins have been developed, to dampen the inflammatory response. Natalizumab is one such agent, and in small studies in patients with ulcerative colitis has been shown to have some efficacy in leading to clinical remission. Another more gut-selective humanized antibody (MLN02) has been evaluated in multi-center trials and has also been found to lead to clinical and endoscopic remission in more patients than placebo. More studies must be conducted to evaluate long term effectiveness and side effects of these medications. This medication is not yet approved by the FDA for treatment of ulcerative colitis.