What is the best medication for a patient with constipation?

Best Medication for Constipation

Polyethylene glycol (PEG) 17g once daily is the best first-line medication for constipation, offering superior efficacy and safety compared to all other laxatives. 1

First-Line Treatment: Osmotic Laxatives

PEG should be the initial pharmacological choice for most patients with constipation, as it is the most extensively studied laxative with the best results and fewest side effects. 2, 3 PEG works by forming an isotonic solution that prevents water absorption, increasing intestinal volume and facilitating evacuation without causing electrolyte disturbances. 3

• Dosing: Start with PEG 17g once daily, titrating according to symptoms 1
• Common side effect: Abdominal pain is the most frequent adverse effect 4
• Alternative osmotic laxatives include lactulose 30-60mL twice to four times daily, though PEG remains superior 2, 1

Critical Pitfall with Fiber Supplements

While soluble fiber (psyllium/ispaghula) 3-4g daily is often recommended, it requires adequate fluid intake (8-10 ounces per dose) and can cause intestinal obstruction if taken without sufficient fluids. 1, 5 Psyllium should be increased gradually to avoid bloating and gas. 4 Insoluble fiber (wheat bran) should be avoided entirely as it consistently worsens constipation symptoms. 4

Second-Line Treatment: Stimulant Laxatives

When PEG alone is insufficient after 2-4 weeks, add bisacodyl 10-15mg daily or senna 15-30mg daily. 2, 1 These stimulant laxatives are generally preferred over other options. 2

• Bisacodyl: Target one non-forced bowel movement every 1-2 days; can increase to 10-15mg twice or three times daily if needed 4, 1
• Senna: Alternative stimulant, but prolonged use may cause colonic dependency and rebound constipation 1
• Magnesium salts: Use cautiously and avoid in renal impairment due to hypermagnesemia risk 2, 1

Important Caveat About Docusate

Docusate (Colace) lacks efficacy and should not be used, as evidence demonstrates it provides no additional benefit compared to other laxatives. 4

Third-Line Treatment: Prescription Secretagogues

For refractory constipation failing first and second-line therapies after 3 months, linaclotide 145mcg (for chronic constipation) or 290mcg (for IBS-C) once daily on an empty stomach is the preferred prescription agent. 4, 1, 6 Linaclotide is FDA-approved and has the strongest evidence among secretagogues. 6

• Lubiprostone 8mcg twice daily is an alternative for women with IBS-C, though it has higher rates of nausea (19% vs 14% placebo) and did not meet clinically meaningful thresholds in some outcomes 4, 7
• Diarrhea is the most common side effect of linaclotide, occurring as part of its mechanism of action 4, 1
• Review efficacy after 3 months and discontinue if no response 4

Special Populations

Opioid-Induced Constipation

All patients receiving opioids should be prescribed a concomitant laxative prophylactically unless contraindicated by pre-existing diarrhea. 2 Osmotic or stimulant laxatives are preferred first-line options. 2 For laxative-refractory cases, methylnaltrexone 0.15mg/kg subcutaneously every other day can be used. 1

• Bulk laxatives like psyllium are not recommended for opioid-induced constipation 2
• Combined opioid/naloxone medications reduce the risk of opioid-induced constipation 2

Elderly Patients

PEG 17g daily offers the most efficacious and tolerable solution for elderly patients with an excellent safety profile. 2 Special considerations include:

• Ensure toilet access, especially with decreased mobility 2
• Monitor for dehydration and electrolyte imbalances when diuretics or cardiac glycosides are prescribed 2
• Avoid liquid paraffin in bed-bound patients or those with swallowing disorders due to aspiration pneumonia risk 2
• Avoid bulk agents in non-ambulatory patients with low fluid intake due to mechanical obstruction risk 2

Fecal Impaction

When digital rectal exam identifies a full rectum or fecal impaction, suppositories and enemas are preferred first-line therapy. 2 Best practice involves disimpaction through digital fragmentation and extraction, followed by maintenance bowel regimen. 2

• Glycerin suppository is first-line for rectal intervention 1
• Bisacodyl suppository 10mg rectally once or twice daily is an alternative 1
• Enemas are contraindicated in neutropenia, thrombocytopenia, paralytic ileus, recent colorectal/gynecological surgery, severe colitis, or recent pelvic radiotherapy 2

Essential Supportive Measures

Beyond pharmacotherapy, patients should increase fluid intake to at least 2 liters daily, particularly those in the lowest quartile of fluid consumption. 1 Physical activity should be encouraged within patient limitations, even bed-to-chair transfers. 2, 1 Privacy and comfort for defecation, proper positioning (small footstool to assist gravity), and anticipatory management are critical non-pharmacological interventions. 2