Laxatives: Nursing pharmacology

Laxatives are a group of medications that help the passage of stool, and are used to relieve constipation. Now, based on their mechanism of action, laxatives can be broadly divided into four main groups: osmotic laxatives, stimulant laxatives, bulk-forming agents, and emollients or stool softeners.

Most of these medications are taken orally, but some of them can also be given rectally in the form of enemas or suppositories, to cleanse the bowels before procedures like colonoscopies or surgeries.

Starting with osmotic laxatives, these include saline laxatives, such as magnesium hydroxide, magnesium citrate, and sodium phosphate salts; and indigestible sugars and alcohols, like lactulose and polyethylene glycol.

Both saline laxatives and indigestible sugars and alcohols are not well absorbed or digested, so they draw more water out of the intestinal cells and into the lumen via osmosis.

This increases intestinal motility, called peristalsis, which pushes the stool through the gastrointestinal tract and also helps mix the stool with water.

Moving on to bulk-forming agents, these include methylcellulose, polycarbophil, and psyllium. Now, these medications can’t be digested by the enzymes in our gastrointestinal tract, so they remain in the intestinal lumen and end up getting incorporated into the stool.

As a result, bulk-forming agents work by drawing in more water, making the stool swell up into a soft, bulky mass, which is easier to pass, while also stimulating peristalsis.

Next are stimulant laxatives like bisacodyl, and senna. These medications are also known as irritant laxatives, since they work by irritating the nerve endings in the large intestinal walls.