Antidiarrheals: Nursing pharmacology

Antidiarrheals are a group of medications that are used to treat diarrhea, which is characterized by loose, watery stool, or an increased frequency of bowel movement.

Now, based on their mechanism of action, antidiarrheals can be broadly divided into four main groups: opiates and opiate-related agents, somatostatin analogues, adsorbents, and bulk-forming agents.

Let’s start with opioids like loperamide, diphenoxylate, difenoxin, and paregoric. These are taken orally and work by stimulating the opioid receptors found in the intestinal wall, which decreases peristalsis or bowel movement.

The slowed transient time allows for increased absorption of fluid and electrolytes into the fecal mass.

Next, there are somatostatin analogues, such as octreotide. This can be administered orally, subcutaneously, intramuscularly, or intravenously, and it’s mostly used to treat diarrhea associated with certain tumors or chemotherapy.

The way octreotide works is by binding to somatostatin receptors and mimicking somatostatin’s effects.

These include inhibiting hormone release by the pancreas and gastrointestinal tract, as well as slowing down peristalsis and decreasing the secretion of fluid and electrolytes into the bowel lumen.

Moving on to adsorbents, these include bismuth subsalicylate, and are taken orally. Once in the intestinal lumen, bismuth subsalicylate has protective properties, since it can coat the walls of the intestines, as well as antimicrobial properties, since it can kill causative bacteria.

In addition, bismuth subsalicylate has antisecretory actions, so it helps reduce how much fluid is secreted into the bowel lumen.

Finally, bulk-forming agents include methylcellulose, polycarbophil, and psyllium. Now, these medications can’t be digested, so they remain in the intestinal lumen and end up getting incorporated into the stool.

As a result, bulk-forming agents work by absorbing water, making the stool swell up into a bulky mass. In addition, bulk-forming agents can be used as laxatives.

Now, the most common side effect of antidiarrheals is constipation. In addition, opioid agents can also cause central nervous system and respiratory depression if combined with other CNS depressants, like benzodiazepines, barbiturates, and alcohol.

Now, loperamide has a boxed warning regarding torsades de pointes and sudden death with high doses.

On the other hand, octreotide can impair gallbladder function, which may lead to cholelithiasis. Finally, bismuth subsalicylate may temporarily stain the tongue and stools black.

As far as contraindications go, these are mostly for the opioids. So, they should not be given to clients with severe hepatic or renal impairment, since they can induce hepatic coma.

Now, loperamide should not be used in clients younger than 2 years old or those with risk factors for QT prolongation.

On the other hand, diphenoxylate and difenoxin should be used with caution in children younger than 4 and in older adults, since these clients are at an increased risk for CNS and respiratory depression.

In addition, diphenoxylate and difenoxin are typically given in the form of preparations that contain atropine, so these should be avoided by clients with narrow angle glaucoma, since atropine can worsen the obstruction of aqueous humor drainage.