Osmotic laxatives
Among the laxatives that have the weakest effect but are very well tolerated are so-called osmotic (saline) laxatives (laxatives). Osmotic laxatives are not absorbed into the blood during intestinal transit. As a result, there is a larger number of particles in the stool, a process known as the development of osmotic pressure.
Because there are more particles in the bowel than in the blood, the water now tries to compensate for this imbalance. Therefore more water flows from the blood back into the intestine. Because of the water, a larger amount of particles is added to a larger amount of water, so that on average there is an equal concentration of particles in the intestine and in the blood, as there is now comparatively more water in the intestine to which the particles can be distributed.
This principle is known in science as osmosis, i.e. a concentration balance between two compartments, in our case the intestine and the blood. Because of the principle of osmosis, these types of laxatives are called osmotic laxatives. The fact that there is now more water in the intestine (due to the previous osmotic pressure) makes the stool more supple, as more water is added.
Examples of osmotic laxatives include Glauber’s salts (sodium sulphate) or bitter salts (magnesium sulphate). The sugar alcohols sorbitol and mannitol also have an osmotic effect. Sugars in pure form, such as lacutose, galactose or lactose, can also be used as laxatives.
They also have a weak osmotic effect, but more importantly, they lead to acidification of the stool in the intestine, as the bacteria in the intestine break down the sugar into acidic components. This stimulates intestinal activity and results in faster processing and transport of the intestinal contents. This is how the sugars develop their laxative effect.
As some osmotic laxatives can cause a loss of water and electrolytes, it is important that patients drink a lot and make sure that the drinking water is as rich in sodium and magnesium as possible to compensate for the electrolyte loss to some extent. Depending on the active ingredient and the response to the laxatives, it takes about 3-48 hours before a bowel movement (defecation) occurs. The side effects are usually very minor.
In addition to the water and electrolyte losses already mentioned, flatulence (flatus) and rarely cramps in the abdomen area can also occur. Isoosmotic laxatives are substances that can bind water in the intestine. This prevents the water from leaving the intestine and entering the blood from the intestine.
As more water remains in the intestine, the intestine is stimulated to work more, which promotes peristalsis, and the stool is made very supple and can therefore be transported more easily out of the anus. As isoosmotic laxatives only act in the rectum, there is no impairment of the remaining intestinal passage, which has a positive effect on the side effect profile, i.e. the side effects are reduced. The mini-enema is a particularly fast-acting laxative. Within 5-20 minutes the patient will have a bowel movement, which is a great advantage especially for diagnostic purposes, such as a colonoscopy, as the patient does not have to wait long before being examined.
