Drugs Affecting GIT Motility

Drugs Affecting GIT Motility

• Drugs can increase or decrease gastrointestinal (GI) tract motility.
• Drugs that increase motility are called prokinetic drugs.
• Prokinetic drugs are used in the upper GI tract.
• Laxatives are drugs that increase motility in the lower GI tract.
• Drugs that decrease motility include antispasmodics and antidiarrheal drugs.
• Antispasmodics are used to treat spasms and cramps in the GI tract.
• Antidiarrheal drugs are used to treat diarrhea.

Laxatives

• Laxatives are used to treat constipation.
• They work in different ways, including:
  • Bulk-forming agents: Dietary fibers, methylcellulose, bran
  • Osmotic laxatives: Magnesium sulfate, lactulose
  • Irritant (or stimulant) laxatives: Castor oil, Senna, Bisacodyl
  • Stool softeners: Docusate sodium
  • Lubricant laxatives: Liquid paraffin, Glycerin suppositories
  • Others: 5-HT4 agonists (prucalopride, cisapride), opioid antagonists (methylnaltrexone), chloride channel activator (lubiprostone)
• Patient should take large amounts of water with bulking agents.
• Lactulose is commonly used during pregnancy.
• Stimulant laxatives are contraindicated in pregnancy.

Mechanism of Action of Laxatives

• Bulk-forming agents: Retain water in the gut and distend the large intestine, activating stretch receptors and stimulating peristalsis.
• Osmotic laxatives: Retained in the gut lumen, retaining water through osmosis, triggering stretch receptors and increasing peristalsis.
• Stimulant laxatives: Cause irritation of the intestinal mucosa and inhibit Na+/K+ ATPase, leading to water and electrolyte accumulation in the gut lumen, directly stimulating peristalsis.
• Stool softeners: Anionic surfactants that allow more water and fats to be incorporated into stool, making it easier to pass through the GI tract.
• Lubricant laxatives: Glycerin draws water from the rectal mucosa, lubricating the anal canal, stimulating reflex rectal contractions, and promoting stool evacuation within 15-20 minutes.
• Other Specific agents:
  • Lubiprostone (Chloride Channel Activator): indicated for chronic constipation and irritable bowel syndrome, but contraindicated in pregnancy.
  • Methylnaltrexone: blocks opioids from interacting with mu-receptors in the intestines, used for opioid-induced constipation.

Antimotility Drugs

• Used to treat diarrhea by decreasing gut motility.
• Diphenoxylate: Given with atropine to discourage abuse. CNS effects are not prominent in therapeutic doses and used for diarrhea. Contraindicated in children due to potential respiratory depression, paralytic ileus, and toxic megacolon.
• Loperamide: Has selective action on the GI tract with additional antisecretory activity. Minimal CNS effects, making it suitable for diarrhea.
• Racecadotril: Active compound that inhibits enkephalinase, an enzyme that degrades enkephalins (the endogenous opioids). Leads to antisecretory activity on the intestines without reducing intestinal motility.

Antispasmodics

• Anticholinergics: Drugs like atropine and hyoscine inhibit acetylcholine, relaxing smooth muscles.
• Direct smooth muscle relaxants: Drotaverine and mebeverine directly relax smooth muscles of the GI tract.

Drugs for Diarrhea

• Replacement of fluids
• Treatment of the cause
• Symptomatic relief:
  • Adsorbants: Kaolin, pectin, activated charcoal
  • Antimotility drugs
  • Antispasmodics

Clinical Correlates and MCQ Examples

• Specific cases and multiple-choice questions (MCQs) illustrate the application of these drugs in clinical scenarios. These scenarios involve various conditions (constipation, diarrhea, etc.) and patient characteristics for particular drug prescriptions.

Explore the different classes of drugs that affect gastrointestinal motility. This quiz covers prokinetic drugs, laxatives, antispasmodics, and antidiarrheal medications, detailing their uses and mechanisms. Test your knowledge on how these drugs work and their applications in treating GI disorders.