Laxatives are one of the most widely prescribed drugs, both on the wards in hospital as well as in general practice. Most doctors will have had to prescribe it at least once in their career. This makes them quite an important drug to be aware of.
Annoyingly, these terms can be found used interchangeably, and thereby can cause some confusion! In essence though, they work to the same effect: to increase intestinal emptying. The main difference between them is potency; cathartics are the most potent, followed by purgatives and then laxatives.
Laxatives have 3 uses in particular:
What I find helpful when it comes to deciding which laxative would be most appropriate for each situation is understanding how the gut works normally, knowing why the laxative is required and then fitting in where each type of laxative exerts its action.
Normal gut motility depends on several factors:
These factors lead to peristalsis, a vital process that leads to defecation. Any disruption can lead to an alteration of bowel habit -and essentially, that's what the laxatives do!
Constipation has a wide variety of causes, and the laxative prescribed often depends on the cause. Also, before prescribing a laxative, it is important to first rule out a treatable cause.
For example, patients who have constipation secondary to poor diets should first be encouraged to increase their fibre and fluid intakes before going on to a laxative. In addition, because the different laxatives have different mechanisms of action, some will be more appropriate for the cause of constipation than another, e.g. peripheral opioid receptor antagonists will be best for constipated patients who have no choice but to take opioids chronically.
Some causes of constipation are listed here:
There are 3 main types of laxatives, as depicted here in the diagram below:
Summary tables with details for some of the more common drugs in each type are provided below for quick reference:
Faecal softeners: act to soften and lubricate faeces
Peripheral opioid receptor antagonists: blocks opioid receptors
5HT4- receptor agonists: selectively stimulates serotonin receptors to increase colonic motility
Again, summary tables with details of some of the individual drugs in each type are provided below.
Pregnancy: Most laxatives are safe to use in pregnancy, although manufacturers advise caution and not to prescribe more than needed. The main laxative to avoid in pregnancy is the 5HT4 receptor agonist prucalopride.
Eating Disorders: It is quite easy to forget but laxatives can be abused by those desiring to lose weight. Ask about laxative use if you suspect an eating disorder.
Always remember that laxatives are available OTC, and always check with the patient if they are on any of those before prescribing them some.
Laxative overuse can result in diarrhoea, electrolyte disturbances and dehydration and therefore even though it is considered quite a safe drug, the prescriber must always be cautious!
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