What laxative is recommended for a patient with constipation?

First-Line Laxative Recommendation for Constipation

For most patients with constipation, start with polyethylene glycol (PEG) 17 grams mixed in 8 ounces of water once or twice daily, or alternatively a stimulant laxative such as senna. 1

Initial Laxative Selection

Polyethylene Glycol (PEG) as First Choice

• PEG is the preferred first-line agent for chronic constipation based on the strongest evidence, with proven efficacy increasing complete spontaneous bowel movements by 2.9 per week compared to placebo 1
• The standard dose is 17 grams (one capful) mixed in 8 ounces of water, taken once or twice daily 1
• PEG demonstrates durable response over 6-12 months without tachyphylaxis, making it suitable for long-term use 1, 2
• Side effects are generally mild and include abdominal distension, loose stool, flatulence, and nausea 1

Stimulant Laxatives as Alternative First-Line

• Senna is an equally acceptable first-line option, particularly for patients who prefer a non-osmotic mechanism 1
• Typical dosing is 2 tablets every morning, with maximum of 8-12 tablets per day 1
• Other stimulant options include bisacodyl (2-3 tablets daily) or sodium picosulfate 1

Critical Context-Specific Considerations

Opioid-Induced Constipation

• All patients starting opioids should receive prophylactic laxatives immediately 1
• Stimulant laxatives (senna) or PEG are preferred; patients do not develop tolerance to opioid-induced constipation 1
• Increase laxative dose when increasing opioid dose 1
• If traditional laxatives fail, peripheral opioid antagonists (naldemedine, naloxegol, or methylnaltrexone) should be added 1, 3

What NOT to Use

• Avoid psyllium and other bulk-forming laxatives in most constipation cases, especially opioid-induced constipation 1
• Psyllium is ineffective for opioid-induced constipation and may worsen symptoms if inadequate fluid intake 1, 4
• Docusate (stool softener) has been shown to be ineffective and is not recommended 1, 5

Escalation Strategy When First-Line Fails

Second-Line Additions

• Add bisacodyl 10-15 mg daily to three times daily if PEG and senna are insufficient 3
• Consider magnesium-based laxatives (magnesium hydroxide 30-60 mL daily or magnesium citrate 8 oz daily), but use cautiously in renal impairment due to hypermagnesemia risk 1, 3
• Lactulose 30-60 mL twice to four times daily can be added, though it causes more flatulence and bloating than PEG 3, 6

Before Escalating Therapy

• Rule out fecal impaction (especially if diarrhea accompanies constipation) and bowel obstruction through digital rectal exam and consider abdominal imaging 3, 7
• Discontinue non-essential constipating medications 3, 7
• Assess for metabolic causes: hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus 3, 7

Special Population Considerations

Elderly Patients

• PEG 17 grams daily offers an efficacious and tolerable solution with good safety profile 1
• Ensure toilet access and optimize toileting habits (attempt defecation twice daily, 30 minutes after meals) 1
• Avoid liquid paraffin in bed-bound patients or those with swallowing disorders due to aspiration pneumonia risk 1

Cancer Patients

• Goal is one non-forced bowel movement every 1-2 days 1
• Enemas are contraindicated in neutropenia, thrombocytopenia, recent colorectal/gynecological surgery, or recent pelvic radiotherapy 1, 3

Common Pitfalls to Avoid

• Do not combine docusate with senna—studies show senna alone is more effective than the combination 1
• Do not use fiber supplements without adequate fluid intake (at least 8-10 ounces per dose), as this can worsen constipation or cause obstruction 1, 4
• Do not give oral laxatives alone for fecal impaction—the impaction must be mechanically disrupted first with digital disimpaction and enemas 3
• Do not forget prophylaxis when prescribing opioids—waiting for constipation to develop makes it harder to treat 1