What is the recommended dose of laxatives for an adult patient with constipation and no significant medical history?

Recommended Laxative Dosing for Adult Constipation

For an adult with constipation and no significant medical history, start with polyethylene glycol (PEG) 17 grams once daily, and if inadequate response after 24-48 hours, add bisacodyl 10 mg once daily. 1, 2

First-Line Treatment: Polyethylene Glycol (PEG)

PEG 17 grams (one capful or packet) dissolved in 4-8 ounces of any beverage once daily is the preferred initial therapy. 1, 2, 3

• Take with or without food, ensuring powder is fully dissolved before drinking 3
• Response has been shown to be durable over 6 months 1
• Common side effects include abdominal distension, loose stool, flatulence, and nausea 1
• Can be used safely long-term without a predetermined stop date 2
• Do not use for more than 7 days without medical supervision per FDA labeling 3

Second-Line: Add Stimulant Laxative

If PEG alone is insufficient after 24-48 hours, add bisacodyl 10 mg once daily at bedtime. 1, 2

• Start at lower dose (5 mg) and increase to 10 mg if needed 1
• Maximum dose is 10 mg orally daily 2
• Most common side effects are abdominal pain, cramping, and diarrhea 1
• Strongly recommended for short-term use (4 weeks or less) or as rescue therapy 1
• Can be used as occasional rescue therapy in combination with PEG 1

Alternative First-Line Options

Magnesium Oxide

Start with 400-500 mg once daily, can increase to 1,000-1,500 mg daily if needed. 1, 4

• Begin at lower dose and titrate upward as necessary 1
• Contraindicated in renal insufficiency due to hypermagnesemia risk 1, 4
• Works through osmotic mechanism to draw water into intestinal lumen 4

Senna

Start with 10-15 mL (2-3 teaspoons) once daily at bedtime, maximum 15 mL twice daily. 1, 5

• Trial doses evaluated were higher than commonly used in practice; start low and titrate up 1
• Abdominal pain and cramping may occur with higher doses 1
• Can be used for longer than 4 weeks though more data needed on long-term tolerance 1

Third-Line: Lactulose (If OTC Therapies Fail)

Lactulose 15-30 mL (10-20 grams) once daily, can increase to 60 mL (40 grams) daily if needed. 1, 2

• Bloating and flatulence are dose-dependent and common, which may limit use 1
• Takes 2-3 days to work 2
• Less preferred than PEG due to side effect profile 1, 2

Critical Treatment Algorithm

1. Start PEG 17 grams once daily 1, 2, 3
2. If no response after 24-48 hours, add bisacodyl 10 mg at bedtime 1, 2
3. If still inadequate after 48 hours, perform digital rectal exam to rule out impaction 2
4. If impaction present, use glycerin suppositories or manual disimpaction 2
5. If no impaction but persistent constipation, consider rectal bisacodyl suppository or small-volume enema 2
6. If constipation persists beyond 4 weeks, consider switching to or adding magnesium oxide, or refer for further evaluation 2, 4

Important Safety Considerations

Rule out mechanical bowel obstruction before initiating any laxative therapy. 1, 2, 4

• Assess for red flags: severe abdominal pain, nausea, vomiting, abdominal distension 4
• Check for fecal impaction, especially if diarrhea accompanies constipation (overflow) 4
• Avoid magnesium-based products in renal impairment 1, 2, 4
• Avoid rectal interventions in neutropenic or thrombocytopenic patients 1, 2

Common Pitfalls to Avoid

Do not use docusate (stool softener) alone—it lacks efficacy evidence and is not recommended. 1, 2

• Multiple guidelines explicitly state docusate has not shown benefit 1, 2
• Adding docusate to senna was less effective than senna alone in clinical trials 2, 6

Do not use bulk laxatives (psyllium/Metamucil) for constipation management. 1, 2

• Ineffective for constipation and may worsen symptoms without adequate fluid intake 1, 2
• Particularly not recommended for opioid-induced constipation 1, 2

Do not wait to start laxatives if initiating opioid therapy—provide prophylactic treatment immediately. 1, 2