Laxatives

Laxatives are a type of medicine that helps patients with trouble opening their bowels, usually due to hard stools (constipation), to do so more easily. Different kinds of laxatives work in different ways there is no strong evidence that they improve other symptoms of irritable bowel syndrome (IBS), like pain. Some patients, at least in the initial period find abdominal pain may increase. Sometimes a combination is used to achieve the desired effect. Lifestyle factors may also exacerbate constipation and it is important to ensure the diet contains sufficient fruit and vegetables (mindful of avoiding FODMAPs!), plenty of fluids and that regular exercise is a part of the routine.

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Laxatives may work in a number of different ways, some work by ensuring a larger proportion fo water is retained within the stools either by increasing the stool bulk (bulk forming laxatives) or by ensuring a higher proportion of water remains in the gut lumen, thence softening stools (osmotic laxatives). Other laxatives stimulate gut motility, this speeds up the transit of food and debris through the large bowel, thence leading to its more rapid expulsion. Stool softening agents increase the amount of fluid (not necessarily water) in the stool, thence softening them. A number of other laxatives have very specific mechanisms of action relating particular receptors or channels within the gut mucosa, these include linaclotide, prucalopride and lubiprostone. Naltrexone is non absorbable opioid receptor antagonist which may be used in patients who concurrently use opiates for pain relief, although in general opiates should not be used for relief of chronic abdominal pain due to IBS.

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Bulk forming laxatives include drugs like ispaghula husk (fybogel) and methylcellulose these can sometimes be helpful for constipation but do require the diet to contain sufficient water, perhaps two or three litres a day. Because they work by increasing the bulk o the stool they can sometimes cause bloating and abdominal discomfort. Osmotic laxatives are generally non absorbed molecules that remain within the gut. They work by attract water from the body into the stool by a process of diffusion known as osmosis. Laxatives that work in this way include macrogol, sometimes know as laxido or movicol. Lactulose is another osmotic laxative, however the use of this drug is discouraged in patients with IBS because it is a FODMAP and therefore often causes increased fermentation within the large bowel, abdominal pain and bloating. Stimulant laxatives such as senna and bisacodyl may be effective in the short term but their long-term use is generally discouraged, because of potential sideffects or the development of tolerance to such medicines. Stool softeners such as arachis oil, sometimes used as an enema or docusate may soften the stool by lubricating it.

 

Linaclotide  activates the guanylate cyclase 2c receptor leading to the active secretion of chloride and water into the intestinal lumen, the commonest side-effect is diarrhoea. Two drugs which are only used in exceptional circumstances and are generally only prescribed by gastroenterologists are Lubiprostone and prucalopride. Like linaclotide lubiprostone also works by encouraging the secretion of chloride and water into the gut. Similarly prucalopride is a selective serotonin receptor agonist, which speeds gut transit, this can therefore be useful in patients with slow colonic transit, in high dose it may also have benefits in treating nausea.

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As with all drugs used in the treatment of IBS, no drug works for everybody. The key is in using drugs to address specific symptoms. Many of the laxatives are best used in small doses on a regular, often daily, basis rather than waiting until the bowel has become really constipated and then requiring large doses of laxatives to get things moving, which often leads to diarrhoea. The dose often needs to be adjusted to find the right dose for an individual. In addition it is probably better to optimise the dose of a single drug that works rather than to keep adding more drugs, each with their own side-effects, at sub-optimal doses. Once again drugs should only be used in combination with ensuring the lifestyle factors that exacerbate symptoms of constipation are addressed.