What are the recommended constipation medications, including dosing and duration, for an adult patient with no significant medical history or medication use?

Constipation Medications with Dosing and Duration

For an adult with chronic idiopathic constipation and no significant medical history, start with polyethylene glycol (PEG/MiraLAX) 17 grams once daily mixed in 8 oz of water, which can be continued long-term and titrated up to twice daily if needed after 48 hours without response. 1, 2

First-Line Treatment: Osmotic Laxatives

Polyethylene Glycol (PEG/MiraLAX)

• Dosing: 17 grams (1 capful) mixed in 8 oz water once daily 1, 2
• Titration: If no bowel movement within 48 hours, increase to 17 grams twice daily 2
• Duration: Can be used continuously long-term; response typically seen by week 2 1, 2
• Goal: Achieve 1 non-forced bowel movement every 1-2 days 1
• Evidence strength: Strong recommendation with moderate certainty of evidence from the 2023 AGA-ACG guidelines 1, 2
• Effectiveness: Increases complete spontaneous bowel movements by 2.90 per week and spontaneous bowel movements by 2.30 per week compared to placebo 2
• Side effects: Bloating, abdominal distension, loose stool, flatulence, nausea (generally mild to moderate) 1, 2

Magnesium Oxide

• Dosing: Start at lower dose (typically 400-800 mg daily), increase as needed 1
• Duration: Studied for 4 weeks, but longer-term use is appropriate 1
• Caution: Avoid in patients with renal insufficiency due to hypermagnesemia risk 1
• Evidence strength: Conditional recommendation with very low certainty 1

Lactulose

• Dosing: 10-20 grams (15-30 mL or 1-2 packets) daily, can increase to 40 grams (60 mL) daily if needed 1, 3
• Duration: Can be used long-term 3
• When to use: Consider if symptoms fail to improve with fiber and over-the-counter laxatives 1
• Evidence strength: Conditional recommendation with very low certainty 1
• Side effects: Bloating and flatulence are dose-dependent and very common, which significantly limit use in clinical practice 1

Second-Line Treatment: Stimulant Laxatives

Bisacodyl

• Dosing: Start at lower dose (5-10 mg), increase as tolerated 1
• Duration: Recommended for short-term use (4 weeks or less) or as rescue therapy 1
• Long-term use: While probably appropriate, data on tolerance and side effects with chronic use are limited 1
• Evidence strength: Strong recommendation with moderate certainty 1
• Effectiveness: Increases complete spontaneous bowel movements by 2.54 per week and spontaneous bowel movements by 4.04 per week 1
• Side effects: Abdominal pain, cramping, diarrhea 1
• Clinical role: Excellent option for occasional use or rescue therapy in combination with other agents 1

Senna (Sennosides)

• Dosing: Typically 15-30 mg daily at bedtime 1
• Duration: Can be used as needed or short-term daily 1
• Mechanism: Stimulates myenteric plexus in colon and inhibits water absorption 1
• Side effects: Abdominal cramps, may cause hypokalaemia with excessive use 1

Medications to Avoid

Docusate (Stool Softener)

• Not recommended: Has not shown benefit in available literature 1
• Evidence: Adding docusate to senna was less effective than senna alone 1

Fiber Supplements (Psyllium, Bran)

• Not recommended for most cases: Supplemental medicinal fiber is ineffective and may worsen constipation 1
• Exception: May be considered for mild constipation in patients with low dietary fiber intake, but only psyllium appears effective 1
• Important caveat: Adequate hydration must be maintained with fiber use 1

Advanced Therapies (If First-Line Fails)

Prucalopride (5-HT4 Agonist)

• Dosing: 2 mg once daily (reduce to 1 mg daily if severe renal impairment with CrCL <30 mL/min) 4
• Duration: Can be used long-term 4
• When to use: After failure of osmotic and stimulant laxatives 1
• Important warning: Monitor for suicidal ideation, depression, or unusual mood changes; discontinue immediately if these occur 4
• Side effects: Headache, abdominal pain, nausea, diarrhea, abdominal distension, dizziness 4

Practical Treatment Algorithm

1. Initial assessment: Rule out fecal impaction and obstruction via physical exam; discontinue non-essential constipating medications 2

2. Start PEG 17 grams once daily with goal of 1 bowel movement every 1-2 days 1, 2

3. If no response after 48 hours: Increase PEG to 17 grams twice daily 2

4. If PEG ineffective or not tolerated after 2 weeks: Add or switch to bisacodyl as short-term therapy or rescue agent 1

5. If constipation persists: Reassess for obstruction, hypercalcemia, and other constipating medications; consider magnesium-based products or lactulose 1

6. If still refractory: Consider prucalopride 2 mg daily for chronic management 4

Critical Pitfalls to Avoid

• Do not use fiber supplements routinely: They are ineffective for most constipation and may worsen symptoms 1
• Do not rely on docusate: It lacks efficacy despite widespread use 1
• Avoid sodium phosphate enemas in renal dysfunction: Limit to maximum once daily or use alternative agents 1
• Do not use rectal suppositories/enemas in neutropenia or thrombocytopenia 1
• Monitor for electrolyte abnormalities with magnesium-based products and enemas 1
• Screen for mood changes with prucalopride: Suicidal ideation has been reported 4