Which prescription medication (Rx) should be ordered for constipation?

Prescription Medication for Constipation

Start with polyethylene glycol (PEG) 17 g once daily as your first-line prescription for chronic constipation—it is the gold standard based on superior efficacy, safety, cost-effectiveness, and proven long-term durability. 1

First-Line Prescription: Polyethylene Glycol (PEG)

PEG 17 g daily is the definitive first-line choice recommended by the American Gastroenterological Association for chronic idiopathic constipation. 1 This osmotic laxative works by drawing water into the intestine to increase stool bulk and facilitate passage. 2

Dosing Algorithm for PEG

• Initial dose: 17 g once daily, mixed in 4-8 ounces of liquid 2
• If inadequate response after 2-3 days: Increase to 17 g twice daily (34 g total daily dose) 2
• Titration: Continue adjusting dose upward based on clinical response with no clear maximum dose 1, 2
• Treatment goal: Achieve one non-forced bowel movement every 1-2 days 2
• Duration: PEG has proven durability and safety for 6 months or longer of continuous use 2

Key Clinical Considerations for PEG

• Ensure adequate hydration while on PEG therapy, particularly in patients with low baseline fluid intake 2
• Common side effects include abdominal distension, loose stools, flatulence, and nausea 2
• Monthly cost is $10-$45, making it highly cost-effective compared to prescription secretagogues 2

Alternative First-Line Osmotic Laxatives

If PEG is not tolerated or unavailable:

• Magnesium oxide 400-500 mg daily can be used, but exercise caution in renal insufficiency and pregnancy 1
• Lactulose 15 g daily is another option, though bloating and flatulence may limit tolerability 1

Second-Line Prescription Options: Stimulant Laxatives

Use stimulant laxatives only for short-term rescue therapy or when osmotic laxatives provide inadequate response. 1

• Bisacodyl 5 mg daily (maximum 10 mg daily) for short-term use 1
  • Note: Bisacodyl produces the greatest increase in bowel movements (6.8 spontaneous bowel movements per week after eliminating placebo effect) but shows the most noticeable loss of efficacy between week 1 and week 4 3
• Senna 8.6-17.2 mg daily (maximum 4 tablets twice daily) as second-line treatment, though long-term safety and efficacy data are limited 1

Important Caveat on Stimulant Laxatives

Stimulant laxatives are exclusively designated for as-needed use, not chronic daily therapy. 4 Reserve these for rescue situations or when osmotic laxatives fail.

Third-Line Prescription Options: Secretagogues and Prokinetics

For refractory cases that fail PEG and stimulant laxatives, consider prescription secretagogues or prokinetic agents. 1

Secretagogues (Intestinal Fluid Secretion Enhancers)

• Lubiprostone 24 mcg twice daily increases intestinal secretion and may provide additional benefit for abdominal pain 1
• Linaclotide 72-145 mcg daily (maximum 290 mcg daily) is a guanylate cyclase-C agonist that increases intestinal secretion and may benefit abdominal pain 1, 5
  • Linaclotide is appropriate as first-line prescription treatment specifically for IBS-C, but for chronic idiopathic constipation, osmotic laxatives should be tried first due to considerably lower cost 6
• Plecanatide 3 mg daily (no titration needed) is another guanylate cyclase-C agonist for refractory cases 1
  • Note: Plecanatide yields the lowest increase in bowel movements among prescription agents (approximately 4 times less than bisacodyl) 3

Prokinetic Agent

• Prucalopride 1-2 mg daily (maximum 2 mg daily) is a serotonin type 4 (5-HT4) receptor agonist that enhances colonic motility and may provide additional benefit for abdominal pain 1, 5

Treatment Algorithm Summary

1. Start with PEG 17 g daily as the most cost-effective option with best evidence for long-term use 1
2. If inadequate response after 2-3 days: Titrate PEG dose upward 1
3. If PEG alone fails: Add or switch to stimulant laxatives (bisacodyl or senna) for short-term use 1
4. Before escalating to prescription secretagogues: Rule out fecal impaction and bowel obstruction 2
5. For refractory cases: Consider prescription secretagogues (lubiprostone, linaclotide, plecanatide) or prokinetic agent (prucalopride) 1
6. At 4 weeks: If no improvement despite maximum therapy, reassess and consider switching agents 5

Common Pitfalls to Avoid

• Do not prescribe docusate (stool softener) for established constipation—it is ineffective and not recommended 2
• Avoid supplemental fiber (psyllium) for established constipation, as it may worsen symptoms 2
• Do not use stimulant laxatives as chronic daily therapy—they are for short-term or as-needed use only 1, 4
• Ensure adequate hydration with any constipation therapy to optimize efficacy 5, 2

Supporting Dietary Measures

While not prescription medications, advise patients to maintain adequate fiber intake of 14 g per 1,000 kcal daily, as fiber supplementation can help with chronic constipation when combined with pharmacotherapy. 1