Antispasmodics in IBS

What is the role of antispasmodics in IBS? 

Antispasmodics decrease contractions or spasms in the GI tract, and thereby reduce abdominal cramps. IBS patients have exaggerated sigmoid contractions in response to meals and to stress, which may explain the postprandial discomfort and urgency in some patients. Antispasmodics can be classified into three major subclasses: anticholinergics, direct smooth muscle relaxants, and peppermint oil. 

Anticholinergics work by blocking the acetylcholine mediated depolarization of intestinal smooth muscles. In the United States, the most commonly used anticholinergics are dicyclomine and hyoscyamine. Hyoscyamine and dicyclomine can be taken at regular intervals (four times daily) or intermittently for more episodic symptoms. For patients with postprandial symptoms, the medications can be taken 30 to 45 minutes before a meal. Hyoscyamine also comes in a long-acting form, which can be given twice daily. For patients with less predictable and more intermittent symptoms, hyoscyamine is preferable because it also comes in an easily dissolvable tablet, which can be taken sublingually and acts within minutes. Dicyclomine, an anticholinergic agent, is also a direct smooth muscle relaxant. Hyoscyamine is also available in combination with phenobarbital, scopolamine, and atropine. Although popular, these combination drugs have not been well evaluated in clinical trials and are probably best avoided because of their sedative and addictive potential. 

Peppermint oil blocks entry of calcium into smooth muscle cells, whereas direct smooth muscle relaxants directly inhibit smooth muscle contractibility by increasing cyclic adenosine monophosphate levels or by interfering with the intracellular calcium pool.


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