An Overview of Asacol (Oral Mesalamine)

Prescribing, Dosing, Side Effects, and More

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Asacol is used to treat inflammation in the large intestine in people who have inflammatory bowel disease (IBD). It is most frequently used to treat mild to moderate ulcerative colitis, but it can also be used in certain patients with Crohn's disease. Asacol is one brand of mesalamine; other include Pentasa and Rowasa.

Why Is Asacol Prescribed?

Asacol is used as a maintenance drug, which means that it is helpful in retaining a remission (a period of little or no disease activity) but not in suppressing a flare-up (a period with signs and symptoms of active disease).

It is typically, but not always, used for ulcerative colitis and ulcerative proctitis. The reason why Asacol helps to treat intestinal inflammation is still poorly understood, but it appears that has a topical effect, which means that the medicine must reach the colon to do its job.

According to 2020 guidelines, however, Asacol should be not be used for maintenance by patients with moderate to severe ulcerative colitis who have achieved remission on a biologic and/or immunomodulator medication.

Who Should Not Take Asacol?

Talk to your doctor if you have had a chicken pox vaccination in the past six weeks or if you have kidney disease, as it may not be advisable to take Asacol.

It's suggested that this drug be used cautiously in people who have liver disease. Pyloric stenosis may cause people to retain the Asacol in the body longer.

Use in Pregnancy

The U.S. Food and Drug Administration (FDA) has classified Asacol as a type B drug. The effect that Asacol has on an unborn child has not been studied extensively. Asacol should only be used during pregnancy if it's clearly needed. Notify your prescribing doctor if you become pregnant while taking Asacol.

Asacol contains a substance called dibutyl phthalate. Dibutyl phthalate has been associated with birth defects in animals. Some components of Asacol have been found in human breast milk. The risks and benefits to the mother and the infant should be considered in a nursing pair. 

How Is Asacol Taken?

Asacol is available in oral form, as a suppository, and as liquid or foam enemas. (The oral form will be our focus here.)

In order for Asacol to be effective, the pills must be swallowed whole and not crushed or chewed. The outer coating or shell of the pill may pass through the body whole.

Some people with IBD have reported seeing this outer coating in the toilet. It doesn't mean that the medication is not working or that it's not being absorbed. In some cases, passing the coating could be normal, but it should be mentioned to the doctor that prescribed the Asacol.

Missed Doses

If you miss a dose, take it as soon as you remember unless your next dose is to be taken soon. In that case, just take that dose; don't double up or take more than one dose at a time.

What Are the Side Effects?

Side effects that occurred in more than 2% of patients taking Asacol are:

  • Headache
  • Nausea
  • Nasopharyngitis
  • Abdominal pain
  • Worsening of ulcerative colitis

Some of these may resolve on their own, but call your doctor about any fever, severe headaches, or severe abdominal pain. If your ulcerative colitis seems to get worse, it could be because of acute intolerance syndrome—a condition that affects about 3% of people who take Asacol. Contact your doctor immediately.

Asacol could cause problems with the kidneys, so it's recommended that a doctor monitor kidney function in people taking this drug.

Under the supervision of a physician, Asacol can be safely used long-term.

What Can Asacol Interact With?

Asacol is not known to interact with other medications. People who have had an adverse reaction to Azulfadine (sulfasalazine) may also be sensitive to Asacol.

There are no known food interactions with Asacol.

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  1. Feuerstein JD, Isaacs KL, Schneider Y, et al. AGA Clinical Practice Guidelines on the Management of Moderate to Severe Ulcerative Colitis. Gastroenterology. 2020. 158(5):1450-1461. doi:10.1053/j.gastro.2020.01.006

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