Laxatives

Laxatives are a type of medication used to promote bowel movements in order to alleviate constipation.

Laxatives can also be used before some procedures such as x-rays and colonoscopy where it is necessary to clean out the large bowel.

The use of laxatives has some risks because they can induce diarrhea, leading to potential loss of fluids, electrolytes, and essential nutrients. Therefore, it is important to use them only under medical prescription.

Laxatives, whether natural or medicinal, increase stool volume making easier to move it through the digestive tract and out the body.

There are various mechanisms through which laxatives work:

• Directly affecting the intestinal lining to limit water and electrolyte absorption while encouraging secretion.
• Water retention in the colon.
• Enhancing intestinal motility, which speeds up the transit of fecal matter towards the anus.

The main reason why a laxative is prescribed is when constipation persists despite dietary changes, exercise and other non-pharmacological measures.

Constipation can be defined as difficulty in passing stool.

The main causes of constipation are:

• Low fluid intake
• Disruption in the balance of the intestinal microflora
• Sedentary work
• Lack of physical activity
• Low-fiber diet
• Stress resulting from a fast-paced life
• Medications known to cause constipation as a side effect
• Prolonged reliance on laxatives, leading to a rebound effect where they become less effective over the time

Given that constipation can also signal an underlying condition, it is important to diagnose whether it is primary (without an apparent cause) or secondary to another issue. The treatment approach can significantly differ based on this distinction.

When considering the use of laxatives, the initial choice often focuses on those that enhance stool volume or soften it by retaining water. Medications that stimulate colon movements are reserved for specific situations and usually prescribed in minimal doses to prevent reliance and potential side effects, such as exacerbating constipation.

There are four main types of laxatives:

1. Stimulant agents

   Stimulant laxatives are:

   • Diphenylmethane derivatives: bisacodyl and sodium picosulfate
   • Anthraquinone glycosides: senna and cascara
   • Ricinoleic acid: castor oil

   They stimulate the intestinal muscles, increasing movement and promoting bowel motions. They directly affect the nerve endings, especially in the colon. Their effects are noticeable after 6-12 hours. While highly effective, prolonged use often leads to dependency, making it advisable to avoid extended usage.

   Phenolphthalein and oxyphenisatin were previously used, but were withdrawn from the market due to their associated toxicity concerns.

2. Stool softeners

   Stool softeners such as docusate and mineral oil work by blending fatty residues with intestinal water making the stool softer and easier to pass.

   Lubricants (liquid paraffin, olive oil) help make the stool more slippery so it can easily pass through the colon.

3. Osmotic laxatives

   Osmotic laxatives are:

   • Polyethylene glycol (PEG)
   • Saline laxatives such as magnesium sulfate, magnesium hydroxide, magnesium citrate, sodium sulfate and sodium phosphate
   • Lactulose and sugar alcohols such as sorbitol or mannitol

   They work by drawing water from the rest of the body into the bowel to soften the stool and increase bowel movements.

4. Prokinetic agents

   Prokinetic agents, usually used for other conditions, can also aid in alleviating constipation. Examples include prostaglandins like misoprostol and certain gout medications like colchicine.

   Another category of laxatives (bulk-forming laxatives) increases stool weight and consistency due to their high fiber content, found in substances like methylcellulose, plantago seeds, and agar-agar. However, these laxatives may take several days before noticeable effects are observed.

   Additional laxatives commonly employed include glycerin suppositories, castor oil, lactulose, and lactitol. These substances stimulate the nervous reflexes responsible for physical defecation in the rectum.

   Enemas are preferably used before a medical examination or procedure.