What is the best medication for treating constipation?

Best Medications for Treating Constipation

Polyethylene glycol (PEG) is the first-line medication for treating constipation due to its efficacy, safety profile, and strong evidence supporting its use. 1, 2

First-Line Treatment Options

Osmotic Laxatives

• Polyethylene glycol (PEG): 17g daily with 8oz water

  • Most effective first-line treatment
  • Well-tolerated with minimal side effects
  • Can be safely used long-term
  • Particularly effective and safe in elderly patients 1, 2

• Lactulose: 15-30ml twice daily

  • Alternative to PEG
  • May cause bloating and flatulence (dose-dependent)
  • Generally low cost in generic form 1, 2

• Magnesium hydroxide/citrate:

  • Effective osmotic laxative
  • Should be used cautiously in patients with renal impairment due to risk of hypermagnesemia 1, 2

Second-Line Treatment Options

Stimulant Laxatives

• Bisacodyl: 10-15mg daily

  • Strong recommendation for short-term use (≤4 weeks) or as rescue therapy
  • Leads to large increases in bowel movements
  • Common side effects include abdominal pain, cramping, and diarrhea
  • Start at lower dose and increase as tolerated 1, 2

• Senna: 2-3 tablets twice daily

  • Effective stimulant laxative
  • Can be used alone without stool softeners (docusate not necessary) 1, 2

For Opioid-Induced Constipation

• Peripherally acting μ-opioid receptor antagonists (PAMORAs):
  • Methylnaltrexone: 0.15mg/kg subcutaneously every other day
  • Naloxegol: Effective for opioid-induced constipation
  • Should not be used in patients with bowel obstruction 1, 2

Third-Line Treatment Options (For Refractory Cases)

Secretagogues

• Linaclotide: Guanylate cyclase-C agonist

  • Highly efficacious for chronic idiopathic constipation
  • FDA approved for adults with IBS-C and chronic idiopathic constipation
  • Diarrhea is a common side effect 1, 3

• Lubiprostone: Chloride channel activator

  • Effective for chronic idiopathic constipation and opioid-induced constipation
  • Less likely to cause diarrhea than other secretagogues
  • Nausea is a frequent side effect
  • Dosage: 24mcg twice daily for CIC and OIC; 8mcg twice daily for IBS-C 1, 4

Treatment Algorithm

1. Start with lifestyle modifications:

   • Increase fluid intake
   • Increase physical activity within patient limits
   • Optimize toileting (attempt defecation twice daily, 30 minutes after meals)
   • Ensure privacy and comfort for defecation

2. First-line medication:

   • PEG 17g daily with adequate fluid

3. If inadequate response after 1 week:

   • Add stimulant laxative (bisacodyl 10-15mg daily or senna)

4. For refractory constipation:

   • Consider adding lactulose 30-60mL twice daily
   • For opioid-induced constipation: Add PAMORA (methylnaltrexone or naloxegol)
   • For chronic idiopathic constipation: Consider secretagogues (linaclotide or lubiprostone)

Important Cautions and Considerations

• Avoid bulk-forming laxatives like psyllium for medication-induced constipation as they may worsen constipation if not taken with adequate fluids and can cause intestinal obstruction 5, 6

• Magnesium salts should be used cautiously in patients with renal impairment due to risk of hypermagnesemia 1

• Monitor regularly for bowel movement frequency, consistency, and adverse effects

• Red flags requiring immediate attention: severe abdominal pain, no bowel movement for >3 days, vomiting, and signs of bowel obstruction 2

• Elderly patients require special attention to ensure access to toilets, adequate fluid intake, and appropriate laxative selection 1

The evidence strongly supports PEG as the first-line treatment for constipation, with stimulant laxatives as effective adjuncts. For refractory cases, specialized medications like secretagogues or PAMORAs (for opioid-induced constipation) should be considered based on the underlying cause and patient characteristics.