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Classification of Drugs Used in Constipation
1. Bulk-Forming Laxatives
- Examples: Psyllium, methylcellulose, polycarbophil
- Mechanism of Action: Absorb water into the intestine, increasing stool bulk and promoting peristalsis.
- Adverse Effects: Bloating, gas, and potential intestinal obstruction if not taken with adequate water.
- Contraindications: Patients with intestinal obstruction, fecal impaction, or those who cannot drink adequate water.
2. Osmotic Laxatives
- Examples: Lactulose, polyethylene glycol, magnesium hydroxide, sorbitol
- Mechanism of Action: Draw water into the intestinal lumen via osmotic action, softening the stool and stimulating peristalsis.
- Adverse Effects: Abdominal bloating, flatulence, diarrhea, electrolyte imbalance (especially in chronic use).
- Contraindications: Renal impairment (particularly for magnesium-based laxatives), severe dehydration.
3. Stimulant Laxatives
- Examples: Bisacodyl, senna, castor oil
- Mechanism of Action: Stimulate enteric nerves to increase intestinal motility; may also promote water and electrolyte secretion into the intestine.
- Adverse Effects: Abdominal cramping, electrolyte imbalance, dependence with chronic use.
- Contraindications: Acute abdominal conditions (e.g., appendicitis), intestinal obstruction, undiagnosed abdominal pain.
4. Stool Softeners (Emollients)
- Examples: Docusate sodium, docusate calcium
- Mechanism of Action: Decrease surface tension of stool, allowing water and fat to penetrate and soften it.
- Adverse Effects: Mild gastrointestinal upset, rare hepatotoxicity with prolonged use.
- Contraindications: Intestinal obstruction, use with mineral oil (can increase absorption of mineral oil).
5. Lubricant Laxatives
- Examples: Mineral oil
- Mechanism of Action: Coats the stool and intestinal walls to prevent water absorption, easing stool passage.
- Adverse Effects: Risk of aspiration leading to lipid pneumonia, decreased absorption of fat-soluble vitamins (A, D, E, K) with long-term use.
- Contraindications: Patients at risk of aspiration, children, the elderly, and those with swallowing difficulties.
