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Antispasmodics are a group of drugs used to treat specific symptoms of abdominal pain, bloating and altered bowl habit often in irritable bowel syndrome (IBS). Whilst these drugs may be useful to control specific symptoms they rarely offer complete relief. A wider review of dietary and lifestyle factors should usually be considered in people presenting for the first time with symptoms of IBS.

Antispasmodic drugs work by reducing the intensity or frequency of contraction within the smooth muscle of the bowel wall. This appears to reduce sensations of bloating, colicky abdominal pain and urgency experienced by some patients. This effect is not universal and many people try a number of antispasmodics before either deciding that these drugs are not for them or finding one that seems to have the desired effect.

Why do some antispasmodics work for some people and not for others?

People may have different triggers for their symptoms. For some an increase in the bowel or brain’s response to normal contractions is an issue, for others increases in the frequency and intensity of contractions is a greater part of the problem. For many patients a combination of these factors is at play and together with variations in how each of us metabolises drugs, this influences our response to individual drugs at any given time.

Different antispasmodics have different mechanisms of action. Some, like hyoscine butyl bromide (buscopan), work on the junctions between nerve cells and muscle fibres by blocking the transmission of messages usually triggering muscle contraction by a chemical called acetylcholine (anticholinergics). Others, such as mebeverine alter the balance of salts (particularly calcium) within different compartments of muscle cells and thereby reduce the contractility (force) of muscle fibre contraction. Others (alverine or pinaverium bromide) influence the firing of contractions through their impact on a combination of carefully regulated processes within muscle fibres.

Who should consider them?

People should avoid any drug to which they have been allergic to it in the past. Similarly children and pregnant mums should only take these drugs if instructed to do so by an appropriately trained health professional. In addition hyoscine butyl bromide (buscopan) should be avoided in patients with glaucoma, myasthenia gravis or if you have significant heart disease. 

If frequent colicky abdominal pain or bloating are persistent features of IBS, despite appropriate attempts at lifestyle modification then it may be worth giving antispasmodics a trial. Usually these drugs can be expected to have a fairly rapid effect and certainly if a week’s trial of a particular regular antispasmodic in a standard dose does not give clear benefit then it is unlikely to do so, even if taken for longer. At this stage it may be worth trying a different antispasmodic with a different mechanism of action.

What are the potential side-effects?

Whilst side-effects are uncommon, paradoxically almost all the antispasmodics may cause nausea or worsening bloating in some individuals. Headache may also occur. Nevertheless these side effects are usually mild and disappear quickly once the medication is stopped. Hyoscine butyl bromide may cause palpitations in susceptible individuals.

How should they be taken?

Antispasmodics may be taken regularly or on as required basis. Many patients simply take their chosen antispasmodic when their symptoms flare. Other patients take them regularly, it really depends on how frequently the symptoms they are treating arise and how intrusive those symptoms are. Many of the clinical trials of antispasmodics have shown positive effects over relatively short periods, often several months, however these drugs have been available for several decades and many patients have taken them on a long-term basis without obvious ill effect. Whilst there may be as yet undefined long-term effects these are yet to become evident, and if the drugs help the pain without causing overt side-effects they can be used either regularly or as required.

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