Laxatives: Oral Agents

• Laxatives are drugs that speed up the movement of gut contents through the gastrointestinal tract.

Oral Agents

• Irritant (Stimulant) Laxatives increase peristalsis by irritating the intestinal mucosa, examples of these are bisacodyl and senna.
  • The onset of activity after taking them orally is about 6-10 hours.
  • Taking these chronically can lead to abdominal cramps, cathartic colon, melanosis coli, and laxative dependence.
• Bulk Forming Agents such as methylcellulose and psyllium, increase peristaltic activity by retaining water, causing intestinal distension.
  • They take 1-3 days to work.
  • Adequate hydration is needed when taking these agents.
  • They are the preferred treatment for chronic constipation.
• Osmotic Laxatives increase the volume of intestinal contents, stimulating bowel motility and fluid secretion.
  • Act in about one hour.
  • Saline cathartic laxatives like magnesium sulphate, are used for rapid bowel evacuation before surgery or after anthelmintic administration.
  • Lactulose, is a disaccharide (fructose + galactose), used for chronic constipation.
    • Bacteria in the colon convert lactulose into non-absorbable sugars, creating an osmotic gradient that holds water and stimulates motility.
    • It takes 2-3 days to act.
    • Can also inhibt the growth of ammonia producing organisms, and lower systemic absorption in hepatic encephalopathy.
• Stool Softeners such as docusate, soften feces and ease of passage by mixing aqueous and fatty materials in the intestinal tract.
  • The effect on bowel function after oral use is noted after 2 or 3 days.
  • Used to alleviate occasional constipation.
  • Benefits patients with painful anorectal conditions or after cardiac surgery by easing hard stool passage.
• Chloride Channel Activators like Lubiprostone stimulate secretion of chloride-rich intestinal fluid.
  • Over 50% of patients experience a bowel movement within 24 hours of taking one dose.
  • Used for chronic constipation.
• Guanylate Cyclase (GC)-C Agonists like Linaclotide stimulate secretion of chloride-rich intestinal fluid.
  • Linaclotide is approved for adults and works within 2 days of administration.
  • Used to treat chronic idiopathic constipation.
• Balanced Polyethylene Glycol (PEG) Lavage:
  • PEG solutions are used for complete colonic cleansing before gastrointestinal radiological, surgical, or endoscopic procedures.
  • The ingested solution (2-4 L over 2-4 hours) should be ingested rapidly at least 4 hours before the procedure to promote bowel cleansing.

Local Agents

• Glycerine, hygroscopic and lubricant, bowel action in less than one hour.
• Evacuant enemas like Na phosphate, soften faeces and distend the bowel.
  • used for surgery preparation, radiological examination, and endoscopy