Irritable Bowel Syndrome (cont.)

The most widely studied drugs for the treatment of abdominal pain are a group of drugs called smooth-muscle relaxants.

The gastrointestinal tract muscle is composed of a type of muscle called smooth muscle. (By contrast, skeletal muscles, such as the biceps, are composed of a type of muscle called striated muscle.) Smooth muscle relaxing drugs reduce the strength of contraction of the smooth muscles but do not affect the contraction of other types of muscles. They are used in IBS with the assumption (not proved) that strong or prolonged contractions of smooth muscles in the intestine-spasms-are the cause of pain in IBS. There are smooth muscle relaxants that are placed under the tongue, like nitroglycerin for treatment of angina, so that they may be absorbed rapidly. Smooth muscle relaxants are approximately 20% more effective than a placebo in reducing abdominal pain. It is not clear if smooth muscle relaxants have a beneficial effect on constipation or diarrhea.

Some commonly used smooth muscle relaxants are hyoscyamine (for example, Levsin) and methscopolamine (for example, Pamine). Other drugs combine smooth muscle relaxants with a sedative (for example, hyoscyamine sulfate, atropine sulfate, scopolamine sulfate and phenobarbital [Donnatal]), but there is no evidence that the addition of sedatives adds to the efficacy (effectiveness) of the treatment.

Patients with IBS are frequently found to be suffering from depression, but it is unclear if depression is the cause of IBS, the result of the IBS, or unrelated to the IBS. Several trials have shown that antidepressants are effective in IBS in relieving abdominal pain and, perhaps, diarrhea. The antidepressants work in IBS, however, at relatively low doses that have little or no effect on depression. It is believed therefore, that they are working not by combating depression, but in different ways (through different mechanisms). For example, these drugs have been shown to adjust (modulate) the activity of nerves and to have analgesic (pain-relieving) effects as well. Commonly used psychotropic drugs include the tricyclic antidepressants, amitriptyline (Elavil, Endep), desipramine (Norpramine), and trimipramine (Surmontil). Although studies are encouraging, it is not yet clear whether the newer class of antidepressants, the serotonin-reuptake inhibitors, such as fluoxetine (Prozac), sertraline (Zoloft), and paroxetine (Paxil) are effective.

Source: MedicineNet.com
http://www.medicinenet.com/irritable_bowel_syndrome/article.htm