Treatment of Constipation
Start with polyethylene glycol (PEG) 17g once daily as first-line therapy, combined with increased fluid intake and physical activity when appropriate 1.
Before initiating any treatment, perform a digital rectal examination to rule out fecal impaction and assess for bowel obstruction 1, 2. Check for metabolic causes including hypercalcemia, hypokalemia, hypothyroidism, and diabetes mellitus 3, 1. Review all medications and discontinue non-essential constipating agents (antacids, anticholinergics, antiemetics) 3, 1.
First-Line Pharmacological Options
You have three equally effective first-line choices:
- Polyethylene glycol (PEG) 17g once daily - preferred by the American Gastroenterological Association 1
- Senna or bisacodyl 10-15mg, 2-3 times daily - particularly appropriate for opioid-induced constipation 3, 1
- Milk of magnesia 1 oz twice daily - inexpensive alternative osmotic agent 1
All cost approximately $1 or less per day 1. Do not add stool softeners like docusate to senna, as evidence shows no additional benefit 3, 1.
Special Consideration for Opioid-Induced Constipation
All patients receiving opioid analgesics must be prescribed a concomitant laxative prophylactically unless contraindicated by pre-existing diarrhea 1, 2. Opioid-induced constipation occurs in most patients treated with opioids and should be anticipated rather than treated reactively 3.
Treatment Goal
Aim for one non-forced bowel movement every 1-2 days, not daily bowel movements 3, 1.
Second-Line Treatment
If constipation persists despite first-line therapy, add one of the following 3, 1:
Caution: Avoid magnesium salts in patients with renal impairment due to hypermagnesemia risk 1.
Third-Line Treatment
If gastroparesis is suspected (particularly relevant with GLP-1 agonists like Mounjaro that slow gastric emptying), add metoclopramide 10-20mg, 2-3 times daily as a prokinetic agent 3, 1.
Fourth-Line Treatment for Refractory Cases
For persistent constipation unresponsive to standard laxatives, consider newer secretagogues 1:
- Linaclotide 145 mcg once daily for chronic idiopathic constipation 4
- Linaclotide 290 mcg once daily for IBS-C 4
- Lubiprostone 1
- Plecanatide 1
Linaclotide demonstrated statistically significant improvement in complete spontaneous bowel movements, with CSBM responder rates of 20% vs 3% for placebo in chronic constipation trials 4.
Opioid-Induced Constipation Resistant to Standard Therapy
Methylnaltrexone 0.15 mg/kg subcutaneously every other day (maximum once daily) for opioid-induced constipation that has not responded to standard laxative therapy 3, 2. This peripherally-acting μ-opioid receptor antagonist relieves constipation while maintaining pain control 3.
Naloxegol is another peripherally-acting μ-opioid receptor antagonist option 3.
Management of Fecal Impaction
If impaction is present, use glycerine suppositories or perform manual disimpaction, followed by implementation of a bowel regimen to prevent recurrence 3, 2.
Lifestyle Modifications
- Increase fluid intake to at least 2 liters daily 3, 2
- Increase physical activity within patient's limits (even bed to chair movement helps) 3, 2
- Ensure privacy and comfort for defecation 2
- Use a small stool to facilitate proper positioning during defecation 2
Role of Dietary Fiber
Only consider dietary fiber if the patient has adequate fluid intake (at least 2 liters daily) 1, 2. Supplemental medicinal fiber like psyllium is unlikely to control medication-induced constipation and is not recommended 1. Fiber without adequate hydration can worsen constipation 1.
Critical Pitfalls to Avoid
- Do not rely on fiber supplements alone for medication-induced constipation 1
- Do not add stool softeners to stimulant laxatives - no additional benefit demonstrated 3, 1
- Avoid liquid paraffin in bedridden patients or those with swallowing disorders due to lipoid pneumonia risk 2
- Reassess for impaction or obstruction if constipation persists despite treatment 1
- Monitor patients on diuretics or cardiac glycosides for dehydration and electrolyte imbalances when using laxatives 2