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Laxatives and Purgatives: Classification, Mechanism, Uses, and Adverse Effects
Laxatives and purgatives are used to relieve constipation by promoting bowel movements. They are classified based on their mechanisms of action, which range from increasing stool bulk to stimulating peristalsis directly.
Classification of Laxative and Purgative Drugs
- Bulk-Forming Laxatives
- Examples: Psyllium, Methylcellulose, Polycarbophil
- Mechanism: Absorb water to form a bulky, soft mass, stimulating peristalsis.
- Stimulant Laxatives
- Examples: Bisacodyl, Senna, Cascara Sagrada
- Mechanism: Directly stimulate the enteric nervous system, enhancing peristalsis and fluid accumulation.
- Osmotic Laxatives
- Examples: Magnesium hydroxide, Lactulose, Polyethylene Glycol (PEG)
- Mechanism: Retain water by osmosis, softening stool and increasing volume.
- Stool Softeners (Emollients)
- Examples: Docusate sodium, Docusate calcium
- Mechanism: Reduce surface tension, allowing water and fats to mix with stool.
- Lubricant Laxatives
- Example: Mineral oil
- Mechanism: Coat stool and intestine, preventing water absorption and easing stool passage.
- Saline Purgatives
- Examples: Magnesium sulfate, Sodium phosphate
- Mechanism: Increase osmotic pressure, drawing water into the bowel, promoting movement.
Therapeutic Uses
- Chronic Constipation: Managed with bulk-forming laxatives.
- Acute Constipation: Osmotic or stimulant laxatives for quick relief.
- Bowel Preparation: Osmotic or saline laxatives used before surgeries or colonoscopies.
- Conditions Requiring Easy Defecation: Stool softeners to prevent strain, especially post-surgery or with hemorrhoids.
- Toxin/Drug Elimination: Combined with activated charcoal to clear certain toxins from the bowel.
Adverse Effects
- Bulk-Forming Laxatives: Bloating, gas, risk of bowel obstruction without sufficient water.
- Stimulant Laxatives: Abdominal cramping, diarrhea, potential electrolyte imbalances with prolonged use.
- Osmotic Laxatives: Electrolyte disturbances, dehydration, bloating, and flatulence.
- Stool Softeners: Mild effects like throat irritation and cramping.
- Lubricants: Risk of aspiration, leading to lipid pneumonia, impaired absorption of fat-soluble vitamins with prolonged use.
- Saline Purgatives: Hypermagnesemia, electrolyte imbalance, dehydration, particularly in renal patients.
Conclusion
Laxative and purgative drugs serve as essential tools for managing constipation and facilitating bowel preparation in medical procedures. However, appropriate selection based on mechanism, therapeutic need, and patient profile is crucial to minimize adverse effects and ensure safe use.
