How should acute constipation be managed in an otherwise healthy adult without evidence of bowel obstruction?

Treatment of Acute Constipation in Adults

Start with polyethylene glycol (PEG) 17g mixed in 8 oz of water once or twice daily as first-line therapy for acute constipation in an otherwise healthy adult without bowel obstruction. 1, 2

Initial Assessment

Before initiating treatment, you must rule out mechanical obstruction and fecal impaction, particularly if this represents a new pattern or if alarm symptoms develop 2. Key clinical features to assess include:

• History of abdominal surgery (increases obstruction risk) 3
• Absence of passage of flatus or feces (90% and 80.6% sensitive for obstruction, respectively) 4
• Abdominal distension (present in 65.3% of obstructions) 4
• Abnormal bowel sounds (predictive of small bowel obstruction) 3

Perform a digital rectal examination to check for impaction before starting oral laxatives 5, 1. If impaction is present, use glycerin suppositories or manual disimpaction first 5, 1.

First-Line Treatment: Osmotic Laxatives

Polyethylene glycol (PEG/Macrogol) is the preferred initial agent with strong evidence for efficacy, safety, and tolerability 5, 1, 2. PEG works by drawing water into the intestinal lumen to soften stool without causing the cramping associated with stimulant laxatives 1.

Dosing: One capful (17g) mixed in 8 oz of water, given 1-2 times daily 1, 2

Expected timeline: Response typically occurs within 24-48 hours 1

Side effects: Abdominal distension, loose stool, flatulence, and nausea (generally mild) 2

Alternative osmotic agents include magnesium hydroxide (milk of magnesia) or lactulose, though PEG is superior 5, 1. Avoid magnesium-based products in patients with any degree of renal insufficiency due to hypermagnesemia risk 1, 2.

Escalation Strategy if No Response in 24-48 Hours

If PEG alone fails to produce a bowel movement within 24-48 hours, add bisacodyl as rescue therapy 1, 2:

• Oral bisacodyl: 10-15 mg (2-3 tablets) 5, 1
• Bisacodyl suppository: 10 mg if rectal route preferred 5, 1

Bisacodyl is a stimulant laxative that increases colonic peristalsis and secretion 1. The goal is one non-forced bowel movement every 1-2 days 5, 1, 2.

Rectal Interventions for Persistent Constipation

If oral therapy fails after 48-72 hours and no impaction was initially present, consider:

• Bisacodyl suppository 10 mg as first-line rectal intervention 1
• Small-volume enema (Fleet, saline, or tap water) if suppositories fail 1

Contraindications to rectal interventions: Neutropenia or thrombocytopenia (infection and bleeding risk) 1

What NOT to Do

Do not use docusate (stool softener) as monotherapy. The National Comprehensive Cancer Network explicitly states that docusate has not shown benefit and is not recommended for constipation management 1. Docusate lacks efficacy evidence and should not be prescribed alone 1.

Do not use bulk fiber supplements (psyllium/Metamucil) for acute constipation. Fiber is only conditionally recommended and most appropriate for patients with low baseline dietary fiber intake, not for someone already constipated 5, 2. Fiber requires adequate hydration and has a slower onset of action 5.

Do not use castor oil. It has poor tolerability and limited evidence supporting its use, with modern alternatives having superior efficacy and safety profiles 1.

Treatment Algorithm Summary

1. Rule out obstruction (history, exam, imaging if indicated) 2, 3
2. Check for impaction (digital rectal exam) 5, 1
3. Start PEG 17g in 8 oz water 1-2 times daily 1, 2
4. If no response in 24-48 hours: Add bisacodyl 10-15 mg orally or 10 mg suppository 1, 2
5. If still no response: Consider small-volume enema 1
6. Reassess for obstruction if refractory to above measures 1

Therapeutic Goal and Monitoring

The treatment goal is at least one spontaneous, non-forced bowel movement every 1-2 days 5, 1, 2. Monitor for abdominal cramping or diarrhea, which signal that the dose may need reduction 2.

Safety Considerations

Absolute contraindications to oral laxatives: Intestinal obstruction, ileus, severe dehydration, or acute inflammatory bowel disease 1, 2. These conditions require alternative management, typically rectal interventions or surgical consultation 5.

Ensure adequate fluid intake when using osmotic laxatives to optimize efficacy and prevent dehydration 5, 2.