What are the different laxative groups?
Constipation is often due to the dysfunction of the intestinal nervous system, which slows down intestinal transit time. In such cases, patients usually must be treated with a laxative that stimulates the intestinal ganglia and thus the transport function of the large intestine.
Laxatives support and facilitate evacuation by increasing the stool volume and stimulating the large intestinal muscle by increasing the internal intestinal pressure. This in turn triggers evacuation.
There are four main groups of laxatives:
Bulking agents,
which swell by absorbing water in the large intestine (linseed, psyllium, wheat bran and cellulose derivatives).
Osmotic laxatives,
those extracts water from the tissue and blood vessels to take this to the large intestine (sodium salts; Glauber’s salt, magnesium salts (Epsom salt), lactose, lactulose, mannitol, sorbitol).
Hydragogue purgatives
(laxatives that promote elimination of water) that, as anthraquinone derivatives with an irritant effect on the mucosa, inhibit thickening of the intestinal content and propagate the intestinal waves. These substances are extracted from senna fruit, senna leaves, aloe, buckthorn bark, rhubarb roots or common buckthorn berries).
Laxatives stimulating the large intestinal muscle.
The main effect of Bisacodyl and sodium Picosulphate is the ability to stimulate the muscles of the large intestine.
Bulking agents
These bind water in the large intestine, increasing the bulk of the stools and thus stimulation of the intestinal wall. This intensifies the function of the large intestinal muscle, triggering evacuation.
Bulking agents often need a few days to take effect. Success usually depends on simultaneous intake of plenty of liquid to allow the full bulking activity to develop and to avoid adhesion in the oesophagus or intestine. Particular caution is thus called for in elderly patients with a reduced feeling for thirst and in heart failure patients with restricted liquid intake.
Bulking agents are not considered to be suitable for the treatment of acute constipation, particularly as they only take effect after 2-3 days. Bulking agents are unlikely to prove effective in the presence of disturbances of the nerves in the intestinal wall or diseases of the inner secretory glands. In this case, central control of the intestinal motility, which remains unaffected by bulking agents, is believed to be impossible.
These substances are well tolerated if used as instructed. In rare cases, they can cause flatulence but this disappears after continued use. Caution is called for in diabetic patients who must take account of the bread units in the substances.
Osmotic laxatives
The mode of action of Glauber’s salt and Epsom salt is based on osmotic transport of liquid from the tissue and blood vessels to the intestine. This liquefies the intestinal contents while increasing the bulk of the stools.
The result is similar to that achieved with bulking agents. However, as the liquid with osmotic agents does not come from the intestine alone, but from the surrounding tissue and blood vessels, patients arte advised to drink plenty of liquid at the same time as they are taking these agents. This is the only way to balance out the loss of fluid and prevent thickening of the blood.
Long-term use is not advised as some of the salts contained in the products are absorbed by the body. This can lead to complications in patients with high blood pressure, weak heart muscles or kidney disease.
Lactulose and lactitol have a laxative effect as they are fermented by the intestinal bacteria in the large intestine to form acids, which in turn stimulate the large intestinal muscle. Lactitol is considered to be slightly less effective than lactulose. Both can be used during pregnancy and lactation. These sugar and fruit acids are not believed to be suitable for acute constipation as the onset of action can be delayed by up to 3 days the first time they are used. Many people using these products develop upsetting and painful build-up of gas and flatulence.
Lactose/milk sugar is used primarily for children, pregnant women and patients with impaired liver function. Patients with diabetes must remember that 12 g of lactose contains one bread unit. There seems to be a steady increase in the rate of lactose intolerance.
Sorbitol and mannitol are administered mainly by enemas.
Hydragogue purgatives
Plant-derived laxatives such as senna fruit, senna leaves, aloe, buckthorn bark, rhubarb roots or common buckthorn berries contain anthraquinone glycosides and are considered drastic remedies. They are converted to an active form by bacteria in the large intestine. This is a highly effective chemical compound that binds firmly to the biological cell membranes of the intestine. This triggers a laxative effect, but the mucosa of the large intestine undergoes change. Inflammatory processes set in. The cell bonds in the intestinal mucosa are relaxed, allowing water from the blood and tissue to penetrate the intestine more easily, avoiding thickening of the contents. The simultaneous increase in osmotic pressure in the large intestine intensifies the function of the large intestinal muscle and triggers the evacuation reflex.
The mode of action of anthraquinone derivatives is based primarily on impairment of cell functions. Even minute quantities of anthrone entering the bloodstream can have a cytotoxic effect on other cells (avoid during pregnancy!) This explains why anthraquinone derivatives are described in the literature as potentially cytotoxic and carcinogenic. This prompted the Federal Institute for Drugs and Medical Devices to restrict the indications and the pack sizes to a sufficient quantity for a maximum of 28 days treatment.
Laxatives that stimulate the large intestinal muscle
These products, that contain Bisacodyl and Sodium Picosulphate, take effect only in the large intestine thanks to the way in which they are processed. They promote muscle activity in the large intestine. According to more recent studies, they promote natural intestinal motility by relaxing the longitudinal muscles while stimulating contraction of the anal sphincter. Further Bisacodyl not only inhibits absorption of water from the large intestine, but also enhances secretion of water and electrolytes into the intestine. This prompts an increase in the bulk of the stools while stimulating further intestinal muscle activity.
Unlike the natural, plant-derived anthraquinones with Bisacodyl and Sodium Picosulphate no effect by attacking the intestinal mucosa has been reported, but by impacting on numerous natural processes. The active ingredients do not have to be absorbed to be effective.
As with other laxatives, Dulcolax should not be used where increase in motility and volume principally has no effect or is even contra-productive as well as with severe dehydration and hypersensitivity to the product.
The various dosage forms of Dulcolax each have their own advantages. The special comfort-coated tablets are effective yet gentle with a reliable action, the pearls are particularly gentle and easy to use, the drops allow for optimum individual dosage, the suppositories, with their rapid onset of action, can be used to empty the bowels before rectoscopy.
All forms are well tolerated and reliably effective. In order to rule out the risk of cancer and possible cell damage standardised studies with Bisacodyl or Dulcolax were conducted by the US supervisory authorities (FDA) between 1993 and 1999. Once all the results had been checked, the FDA again allocated the product to the highest class for over-the-counter drugs as “safe and effective” as Dulcolax presents no carcinogenic risk when taken as instructed.
Laxatives (also known as purgatives or aperients):
- Foods
- Bulk-producing agents (Bulk-forming laxatives): brand names include Metamucil, Fiberall, Citrucel, Konsyl, and Serutan.
- Stool softeners / Surfactants: brand names include Colace and Surfak.
- Lubricants / Emollient: Brand names include Fleet and Zymenol.
- Hydrating agents (osmotics)
- Stimulant / Irritant: Brand names include Correctol, Dulcolax, Purge, and Senokot.
- Serotonin 5-HT receptors
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