What is the first-line pharmacological treatment for constipation in adults?

First-Line Pharmacological Treatment for Constipation in Adults

Polyethylene glycol (PEG) is the recommended first-line pharmacological treatment for constipation in adults, with a standard dose of 17g daily mixed in water or other beverage. 1, 2

Treatment Algorithm for Adult Constipation

First-Line Treatment:

• Polyethylene glycol (PEG)
  • Dosage: 17g daily, can be increased to 34g if needed
  • Strong recommendation with moderate certainty of evidence
  • Mechanism: Osmotic laxative that increases stool water content
  • Benefits: Increases complete spontaneous bowel movements by approximately 2.9 per week compared to placebo 1
  • Response has been shown to be durable over 6 months 1, 3
  • Side effects: Abdominal distension, loose stool, flatulence, and nausea 1

Alternative First-Line Option (for mild constipation):

• Fiber supplements (particularly psyllium)
  • Conditional recommendation with low certainty of evidence 1
  • Most effective for individuals with low dietary fiber intake
  • Important implementation points:
    • Assess total fiber intake from diet and supplements
    • Ensure adequate hydration when using fiber
    • Common side effect: flatulence 1
    • Note: Only psyllium appears to be effective among fiber supplements 1

Second-Line Options:

1. Magnesium oxide

   • Dosage: 400-500mg daily 2
   • Conditional recommendation with very low certainty of evidence 1
   • Start at lower dose and increase if necessary
   • Important caveat: Avoid in patients with renal insufficiency due to risk of hypermagnesemia 1, 2

2. Lactulose

   • Dosage: 15-30ml twice daily 2
   • Conditional recommendation with very low certainty of evidence 1
   • For patients who fail or are intolerant to OTC therapies 1
   • Limitation: Bloating and flatulence are common dose-dependent side effects 1
   • Note: PEG has been shown to be more effective than lactulose in multiple studies 4

Rescue Therapy/Short-Term Options:

• Bisacodyl or sodium picosulphate
  • Dosage: 5-10mg daily 2
  • Strong recommendation with moderate certainty of evidence 1
  • Best for short-term use (defined as daily use for 4 weeks or less) 1
  • Useful as occasional rescue therapy in combination with other agents 1

Clinical Pearls and Caveats

• PEG has demonstrated substantial and sustained efficacy over 24 weeks in patients with chronic idiopathic constipation, with 42% of patients achieving ≥3 complete spontaneous bowel movements per week compared to 13% with placebo 5

• Higher doses of PEG (68g) can provide relief within 24 hours for acute constipation, with an average of 2.2 bowel movements in 24 hours versus 0.5 with placebo 6

• PEG is safe and effective for long-term use (6 months) with no significant differences in laboratory findings or serious adverse events compared to placebo 3

• PEG is as effective as enemas for fecal impaction but better tolerated by patients 7

• Docusate is ineffective for constipation management in adults and is not recommended 2

• Bulk-forming laxatives like psyllium are ineffective for medication-induced constipation and should be avoided in such cases 2

• For opioid-induced constipation, PEG remains first-line but may need to be combined with a stimulant laxative if refractory 2

Monitoring

• Monitor for red flags such as severe abdominal pain, no bowel movement for >3 days, vomiting, and signs of bowel obstruction 2

• Weekly monitoring of bowel movement frequency and consistency is recommended 2

• For elderly patients, pay particular attention to medication lists and comorbidities as they are at higher risk for severe constipation and impaction 2