Antidiarrheal Drugs
Antidiarrheal drugs are medications used to alleviate symptoms of diarrhoea by reducing the frequency and fluidity of bowel movements.
Examples
There is no strict classification, but common examples include:
- Loperamide
- Methylcellulose
- Bismuth subsalicylate
- Aluminium hydroxide
Pharmacodynamics
- Loperamide: Binds to opioid receptors in the intestinal wall, slowing bowel motility. This reduces stool frequency and increases anal sphincter tone, thus decreasing urgency.
- Methylcellulose: A bulk-forming laxative that absorbs water in the intestines, forming a gel-like substance, increasing stool bulk and improving consistency.
- Bismuth subsalicylate: Reduces fluid secretion in the intestines, decreases inflammation, and has mild antibacterial properties against some diarrhoea-causing pathogens.
- Aluminium hydroxide: Acts as an antacid, neutralizing stomach acid and reducing gastric mucosal irritation, helpful in treating heartburn, gastritis, or peptic ulcers.
Side Effects
- Common: Constipation, dizziness, drowsiness, nausea, abdominal cramping, bloating, gas, discomfort, dark tongue or stool, tinnitus, loss of appetite, weakness, muscle pain.
- Rare/Severe: Severe constipation, abdominal pain, paralytic ileus, allergic reactions, difficulty swallowing, intestinal blockage, Reye's syndrome (especially in children with viral infections), GI bleeding, systemic aluminum toxicity (especially with renal impairment), phosphate depletion, osteomalacia.