5-ASA oral and rectal medications for Crohn's disease
5-aminosalicylic acid (5-ASA), also called mesalamine, is similar chemically to aspirin. Aspirin is an anti-inflammatory drug that has been used for many years for treating arthritis, bursitis, and tendonitis (conditions of tissue inflammation). Aspirin, however, is not effective in treating Crohn's disease and ulcerative colitis and may even worsen the inflammation. Recent studies suggest that aspirin might actually decrease future risk of developing colorectal cancer in the general population.
On the other hand, 5-ASA can be effective in treating Crohn's disease and ulcerative colitis if the drug can be delivered topically onto the inflamed intestinal lining. For example, mesalamine (Rowasa) is an enema containing 5-ASA that is effective in treating inflammation in the rectum. However, the enema solution cannot reach high enough to treat inflammation in the upper colon and the small intestine. Therefore, most patients with Crohn's disease involving both the ileum (distal small intestine) and colon, must take 5-ASA orally.
If pure 5-ASA is taken orally, however, most of the 5-ASA would be absorbed in the stomach and the upper small intestine, and very little 5-ASA would reach the ileum and colon. To be effective as an oral agent in treating Crohn's disease, 5-ASA has to be modified chemically to escape absorption by the stomach and the upper intestines.
Sulfasalazine (Azulfidine) was the first modified 5-ASA compound used in the treatment of Crohn's colitis and ulcerative colitis. It has been used successfully for many years to induce remissions among patients with mild to moderate ulcerative colitis. Sulfasalazine also has been used for prolonged periods for maintaining remissions.
Most of the side effects of sulfasalazine include nausea, heartburn, headache, anemia, skin rashes, and, in rare instances, hepatitis and kidney inflammation. In men, sulfasalazine can reduce the sperm count. The reduction in sperm count is reversible, and the count usually becomes normal after the sulfasalazine is discontinued or changed to a different 5- ASA compound.
Some 5-ASA compounds, for example, mesalamine (Asacol and Pentasa), do not have the sulfapyridine component and have fewer side effects than sulfasalazine, and are used more frequently for treating Crohn's disease and ulcerative colitis.
Asacol is effective in inducing remissions in patients with mild to moderate ulcerative colitis. It also is effective when used in the longer term to maintain remissions. Some studies have shown that Asacol also is effective in treating Crohn's ileitis and ileo-colitis, as well as in maintaining remission in patients with Crohn's disease.
Pentasa is a capsule consisting of small spheres containing 5-ASA. Pentasa is sulfa-free. As the capsule travels down the intestines, the 5-ASA inside the spheres is released slowly into the intestine. Unlike Asacol, the active drug 5-ASA in Pentasa is released into the small intestine as well as the colon. Pentasa can be effective in treating inflammation in the small intestine and is currently the most commonly used 5-ASA compound for treating mild to moderate Crohn's disease in the small intestine.
Patients with Crohn's disease occasionally undergo surgery to relieve small intestinal obstruction, drain abscesses, or remove fistulae. Usually, the diseased portions of the intestines are removed during surgery. After successful surgery, patients can be free of disease and symptoms (in remission) for a while. In many patients, however, Crohn's disease eventually returns. Pentasa helps maintain remissions and reduces the chances of the recurrence of Crohn's disease after surgery.
Olsalazine (Dipentum) is a capsule filled with a drug in which two molecules of 5-ASA are joined together by a chemical bond. In this form, the 5-ASA cannot be absorbed from the stomach and intestine. Intestinal bacteria are able to break apart the two molecules releasing the active individual 5-ASA molecules into the intestine. Since intestinal bacteria are more abundant in the ileum and colon, most of the active 5-ASA is released in these areas. Therefore, olsalazine is most effective for disease that is limited to the ileum or colon. Although clinical studies have shown that olsalazine is effective for maintenance of remission in ulcerative colitis, some patients experience diarrhea when taking olsalazine. Because of this, olsalazine is not often used.
Balsalazide (Colazal) is a capsule in which the 5-ASA is linked by a chemical bond to another molecule that is inert (without an effect on the intestine) and prevents the 5-ASA from being absorbed. This drug is able to travel through the intestine unchanged until it reaches the end of the small bowel (terminal ileum) and colon. There, intestinal bacteria split the 5-ASA and the inert molecule releasing the 5-ASA. Because intestinal bacteria are most abundant in the terminal ileum and colon, balsalazide is used to treat inflammation predominantly localized to the colon.
Side effects of oral 5-ASA compounds
- The 5-ASA compounds have fewer side effects than Azulfidine and do not reduce sperm counts. They are safe medications for long-term use and are well-tolerated.
- Patients allergic to aspirin should avoid 5-ASA compounds because they are similar chemically to aspirin.
- Rarely, kidney and lung inflammation has been reported with the use of 5-ASA compounds. 5-ASA should be used with caution in patients with kidney disease. It also is recommended that blood tests of kidney function be done before starting and periodically during treatment.
- Rare instances of worsening of diarrhea, cramps, and abdominal pain, at times accompanied by fever, rash, and malaise, may occur. This reaction is believed to represent an allergy to the 5-ASA compound.