What are the various classes of laxatives and examples of each?

Types of Laxatives

Laxatives are categorized into five main classes based on their mechanism of action: bulk-forming agents, osmotic laxatives, stimulant laxatives, intestinal secretagogues, and lubricating agents 1.

1. Bulk-Forming Agents (Fiber)

• Mechanism: Soluble fiber traps water in the intestine and increases stool bulk
• Examples: Psyllium, methylcellulose
• Dosing: 14 g per 1,000 kcal of daily intake 1
• Cost: <$50/month 1
• Key considerations:
  • Requires adequate hydration as fiber intake increases
  • Common side effects include bloating and abdominal discomfort 1
  • Generally considered initial therapeutic option for chronic constipation 2
  • Not recommended in palliative care patients who cannot maintain adequate fluid intake 3

2. Osmotic Laxatives

These agents draw water into the intestinal lumen through osmotic effects.

Polyethylene Glycol (PEG)

• Mechanism: Long-chain polymer that acts as osmotic laxative
• Dosing: 17 g daily initially 1
• Cost: $10-$45/month 1
• Key features:
  • Not metabolized; pH and bowel flora remain unchanged 3
  • Response shown to be durable over 6 months 1
  • Safe and effective as initial or second-line therapy 2, 4
  • Common side effects: bloating, abdominal discomfort, cramping 1

Lactulose

• Mechanism: Saccharine osmotic laxative
• Dosing: 15 g daily 1
• Cost: <$50/month 1
• Key features:
  • Only osmotic agent studied in pregnancy 1
  • Side effects of flatulence, bloating, and cramping may be limiting 1, 3
  • Can cause bloating but has few serious adverse effects 5

Magnesium Oxide

• Mechanism: Osmotic laxative using poorly absorbable ions
• Dosing: 400-500 mg daily initially; prior studies used 1,000-1,500 mg daily 1
• Cost: <$50/month 1
• Critical caution: Use with extreme caution in renal insufficiency and pregnancy due to risk of metabolic disturbances 1, 5

3. Stimulant Laxatives

These agents directly stimulate intestinal motility.

Bisacodyl and Picosulfate

• Dosing: Bisacodyl 5 mg daily initially, maximum 10 mg orally daily 1
• Cost: <$50/month 1
• Key limitations:
  • Recommended for short-term use or rescue therapy only 1
  • Side effects include cramping and abdominal discomfort
  • Prolonged or excessive use can cause diarrhea and electrolyte imbalance 1
  • Long-term safety and efficacy unknown 1

Senna

• Dosing: 8.6-17.2 mg daily; recommended maximum is 4 tablets twice daily 1
• Cost: <$50/month 1
• Cautions:
  • Present in many laxative teas where dose may be difficult to calculate 1
  • Long-term safety and efficacy unknown 1
  • Despite in vitro data suggesting neoplastic potential, epidemiologic data has not established clear link to colonic neoplasia 5

4. Intestinal Secretagogues

These newer agents increase intestinal fluid secretion.

Lubiprostone

• Mechanism: Acts on chloride channel type 2 in the gut
• Dosing: 24 μg twice daily for chronic constipation; 8 μg twice daily for IBS-C 1, 6
• Cost: $374/month 1
• Key features:
  • May have benefit for abdominal pain 1
  • FDA-approved for women with IBS-C at 8 mg twice daily dose 6
  • Diarrhea may occur in subset of patients leading to discontinuation 1
  • Well tolerated for up to 13 months in long-term studies 6

Linaclotide

• Mechanism: Intestinal secretagogue
• Dosing: 72-145 μg daily initially, maximum 290 μg daily 1
• Cost: $523/month 1
• Features: May have benefit for abdominal pain; also approved for IBS-C 1

Plecanatide

• Mechanism: Intestinal secretagogue
• Dosing: 3 mg daily (also maximum dose) 1
• Cost: $526/month 1
• Features: Also approved for IBS-C; diarrhea may occur 1

5. Prokinetic Agents

Prucalopride

• Mechanism: 5-HT₄ agonist
• Dosing: 1-2 mg daily, maximum 2 mg daily 1
• Cost: $563/month 1
• Features: May have additional benefit for abdominal pain; headaches and diarrhea may occur 1

6. Lubricating Agents

• Examples: Mineral oil, glycerin suppositories
• Status: Generally considered obsolete from general medical perspective 3
• Exception: Still important in palliative care for prophylactic treatment or therapy of constipation 3

Common Pitfalls to Avoid

• Bulk-forming agents without adequate hydration can worsen constipation or cause obstruction
• Magnesium-containing laxatives in renal impairment risk dangerous electrolyte disturbances 1, 5
• Long-term stimulant laxative use without medical supervision due to unknown safety profile 1
• Danthron compounds should be avoided due to hepatotoxicity 5