What are the treatment options for an adult patient with constipation and no significant medical history?

Treatment for Constipation in Adults

For an adult with constipation and no significant medical history, start with polyethylene glycol (PEG) 17 grams once daily mixed in 8 ounces of water, and if there is no response after 24-48 hours, add bisacodyl 10-15 mg daily. 1, 2

First-Line Treatment: Polyethylene Glycol (PEG)

PEG is the strongest evidence-based first-line treatment for chronic idiopathic constipation, with a strong recommendation from the 2023 AGA-ACG guidelines. 1

• PEG 17 grams (approximately one heaping tablespoon) should be mixed in 8 ounces of water and taken once daily with food 2, 3
• The dose can be titrated up to twice daily if inadequate response after 48 hours 2, 3
• PEG demonstrates durable response over 6 months and can be used safely long-term without a predetermined stop date 2, 4
• Common side effects include bloating, abdominal discomfort, flatulence, and loose stools, which are generally mild 4
• PEG causes virtually no net electrolyte disturbance, making it safer than magnesium-based alternatives 2

Second-Line Treatment: Add Stimulant Laxatives

If PEG alone is insufficient after 24-48 hours, add a stimulant laxative rather than switching agents 2, 3:

• Bisacodyl 10-15 mg daily is the preferred add-on therapy 2, 3
• Alternatively, senna 15-30 mg at bedtime can be used 3
• Sodium picosulfate also received a strong recommendation in the 2023 guidelines 1
• The goal is to achieve one non-forced bowel movement every 1-2 days 2, 3

Alternative Osmotic Laxatives (If PEG Not Tolerated)

• Magnesium oxide 400-800 mg daily, which can be increased to 1,000-1,500 mg daily as needed 3
  • Critical caveat: Avoid in any degree of renal impairment due to hypermagnesemia risk 1, 2, 4
  • Should not be used long-term without monitoring 2
• Lactulose 15-30 mL once daily, which can be increased to 30-60 mL two to four times daily 3
  • Has a 2-3 day latency period and may cause bloating 2
  • Preferred in pregnancy 3

Conditional Recommendations: Fiber Supplementation

The 2023 AGA-ACG guidelines gave only a conditional recommendation for fiber, with much weaker evidence than PEG 1:

• Only psyllium has demonstrated effectiveness among fiber supplements 4
• Fiber is most appropriate for patients with documented low baseline dietary fiber intake 4
• Fiber intake should be increased slowly over several weeks to minimize bloating and gas 5
• Bulk laxatives are NOT recommended for opioid-induced constipation and may worsen symptoms in non-ambulatory patients with low fluid intake 1, 2

What NOT to Use

Docusate (stool softeners) should be avoided entirely - multiple guidelines explicitly state it lacks efficacy evidence and is not recommended 2, 4:

• The NCCN guidelines state docusate has not shown benefit 2
• ESMO guidelines list docusate under "laxatives generally not recommended" 2
• Relying on docusate alone without addressing bowel motility is insufficient 2

Rectal Interventions for Severe Cases

If oral therapy fails or if digital rectal exam identifies fecal impaction 1, 2:

• Bisacodyl suppository 10 mg or glycerin suppository as first-line 2, 3
• Small-volume enema (Fleet, saline, or tap water) if suppositories fail 2
• Contraindications: Avoid rectal interventions in neutropenic or thrombocytopenic patients due to infection and bleeding risk 1, 2

Third-Line: Prescription Secretagogues and Prokinetics

For refractory constipation not responding to first and second-line therapies 1:

• Linaclotide 145 mcg once daily (strong recommendation) 1, 6
  • FDA-approved for chronic idiopathic constipation 6
  • Improves stool frequency, consistency, and straining 6
• Plecanatide (strong recommendation) 1
• Prucalopride 2 mg once daily (strong recommendation, serotonin-4 agonist) 1, 3
• Lubiprostone 24 mcg twice daily (conditional recommendation) 1, 7
  • Should be taken with food and water to reduce nausea 7
  • Contraindicated in mechanical obstruction 7

Supportive Lifestyle Modifications

While starting pharmacological therapy, recommend 2, 3:

• Increased fluid intake, particularly when using osmotic laxatives 4, 3
• Physical activity when feasible 2, 3
• Adequate dietary fiber from food sources 3
• Scheduled toileting attempts, ideally 30 minutes after meals 1

Treatment Algorithm Summary

1. Start immediately: PEG 17g once daily 2, 4, 3
2. If no response in 24-48 hours: Add bisacodyl 10-15 mg daily 2, 3
3. If still inadequate after 4 weeks: Consider prescription secretagogues (linaclotide, plecanatide, prucalopride) 1, 3
4. For impaction: Use rectal interventions (suppositories or enemas) 2
5. Reassess every 3-6 months: Evaluate for underlying causes, check electrolytes if using magnesium products, and assess continued need for therapy 2

Critical Pitfalls to Avoid

• Do not prescribe docusate alone - it lacks efficacy and wastes time 2, 4
• Do not use magnesium-based laxatives in renal impairment without monitoring for hypermagnesemia 1, 2, 4
• Do not use bulk laxatives without adequate fluid intake - this can worsen constipation 2
• Do not perform rectal interventions in neutropenic or thrombocytopenic patients 1, 2
• Do not delay treatment waiting for lifestyle modifications alone - pharmacological therapy should begin promptly 1