The Power Of Iso-Osmotic Laxatives: How Do They Work?

Osmotic laxatives are medications used to treat or prevent constipation. They work by drawing water into the colon, softening the stool, and making it easier to pass. An iso-osmotic laxative has a similar mechanism of action, but without the net gain or loss of water or electrolytes, reducing the risk of dehydration. An example of an iso-osmotic laxative is Macrogol 3350 with electrolytes (Movicol®).

How does it work?

Iso-osmotic laxatives are medications that treat constipation by increasing the amount of water in the stool, making it softer and easier to pass. The term "iso-osmotic" refers to the balance of fluid on both sides of a membrane, with no net gain or loss of water or electrolytes. This means that there is a lower risk of dehydration and no extra fluid is needed for the laxative to work effectively.

The main active ingredient in iso-osmotic laxatives, macrogol, goes straight to the bowel, where it retains a set amount of water to soften, expand, and lubricate the stool. This triggers peristalsis, the normal bowel movement that helps push the stool out. The macrogol is then expelled from the body, remaining largely unabsorbed.

Iso-osmotic laxatives work differently from other types of laxatives, such as emollient, lubricant, and stimulant laxatives, which have varying mechanisms of action. For example, emollient laxatives, such as docusate, increase the water and fat content of the stool, while stimulant laxatives, such as bisacodyl, force the intestines to contract and push out stools.

It is important to note that laxatives should be taken as directed to prevent side effects, and they are not safe for everyone. It is always recommended to consult a healthcare provider before taking any medication, including laxatives.

What are the ingredients?

The ingredients in iso-osmotic laxatives differ from other types of laxatives in that they do not cause a net gain or loss of water or electrolytes in the body. This means there is less risk of dehydration and no extra fluid is needed for the laxative to work.

The main active ingredient in the iso-osmotic laxative Macrogol 3350 with electrolytes (MOVICOL®) is macrogol. This ingredient goes straight to the bowel, where it softens, expands, and lubricates the stool by retaining a set amount of water. This triggers peristalsis, or the normal bowel movement. The macrogol is then expelled from the body virtually unabsorbed. MOVICOL® is currently the only iso-osmotic laxative available in Australia.

Polyethylene glycol (PEG) is another iso-osmotic laxative ingredient. It is an organic compound derived from petroleum that can be safely ingested to manage constipation. PEG-containing laxatives include Miralax and GlycoLax, which are available over the counter.

What are the side effects?

Osmotic laxatives can cause several side effects, some of which are common to all laxatives and some of which are unique to osmotic laxatives. The overuse of osmotic laxatives can cause dehydration and the loss of electrolytes like sodium, calcium, and potassium. These are some of the minerals that the body needs to regulate heartbeats, muscle contractions, and other key functions. Dehydration can cause symptoms such as feeling weak, having a headache, and darker urine.

Common side effects of osmotic laxatives include nausea, bloating, cramping, flatulence, and diarrhea. These side effects are usually mild and will resolve within a couple of days of stopping the medication. However, overuse of osmotic laxatives can lead to dehydration and other complications.

It is important to follow the dosing instructions carefully when taking osmotic laxatives and to use them only when needed. Eating plenty of fibre-rich foods and staying hydrated can also help to optimize digestive health and reduce the risk of side effects.

If you experience any persistent or troubling side effects while taking osmotic laxatives, it is recommended to speak to a healthcare professional.

Who should avoid it?

Iso-osmotic laxatives are medications used to treat or prevent constipation by drawing water into the colon and softening stools, making them easier to pass. While they are available over the counter and by prescription, they are not safe for everyone.

Firstly, laxatives are not suitable for children unless recommended by a pediatrician. Pregnant women should also be cautious and check with their healthcare provider before taking any laxatives.

Secondly, laxatives can interact with other medications, so it is important to consult a healthcare professional before taking them if you are on any prescription drugs. This is especially true for saline laxatives, which are not suitable for people taking medication to lower sodium levels or other mineral-based drugs. Lubricant laxatives, such as mineral oil, can also interfere with the absorption of fat-soluble vitamins and other prescription drugs, so they should not be taken at the same time as other medications or supplements.

Thirdly, people who are dehydrated or constipated due to dehydration should avoid osmotic laxatives, as they can further deplete the body's fluid levels. Similarly, people who are already consuming enough fibre, water, and exercising regularly may not need laxatives and can instead focus on lifestyle changes to relieve constipation.

Finally, overuse or misuse of laxatives can lead to severe and dangerous side effects, such as dehydration, electrolyte imbalances, chronic constipation, intestinal blockage, and dependency on the laxatives for bowel movements. Therefore, it is crucial to follow the instructions on the medication and not exceed the recommended dosage. If constipation persists or is frequent, it is important to consult a healthcare professional instead of self-medicating with laxatives.

What are the alternatives?

There are several alternative treatments for constipation, which is what iso-osmotic laxatives are used to treat.

Lifestyle Changes

Constipation can often be relieved through lifestyle changes such as eating high-fibre foods, taking probiotics, drinking more fluids, and exercising.

Bulk-Forming Laxatives

These laxatives increase the amount of water in the stool, making it softer and easier to pass. They include bran, ispaghula husk, psyllium, sterculia, and polycarbophil (FiberCon®).

Faecal (Stool) Softeners

These laxatives enable additional water and fat to be mixed into the stool, making it easier to pass. They include docusate sodium, poloxamer, glycerol, lactulose, magnesium sulfate, and sorbitol.

Lubricant Laxatives

Lubricant laxatives coat the colon, making it slick. The coating prevents the colon from absorbing water from the stool, so it stays soft. They include mineral oil.

Stimulant Laxatives

Stimulant laxatives activate the nerves that control the muscles in the colon. They include bisacodyl (Dulcolax®), senna (Fletcher's® Laxative), and sodium picosulfate.

Prescription Laxatives

If you have chronic constipation, you may need a prescription laxative. These include lactulose (Duphalac®), linaclotide (Linzess®), lubiprostone (Amitiza®), prucalopride (Prudac®, Motegrity®), and plecanatide (Trulance®).

Non-Medical Therapies

There are also non-medical therapies for constipation, including herbal supplements, homeopathy, massage therapy, reflexology, and yoga. However, it is important to ensure that these treatments do not interact with any medical therapy you may be receiving.

Frequently asked questions