Treatment of Constipation
Start with either polyethylene glycol (PEG) 17g once daily or a stimulant laxative (senna or bisacodyl 10-15mg, 2-3 times daily) as first-line therapy, aiming for one non-forced bowel movement every 1-2 days. 1
Initial Assessment Before Treatment
Before prescribing any laxative, perform a digital rectal examination to rule out fecal impaction 2, 1. If the rectum is full or impacted, suppositories and enemas are first-line therapy rather than oral laxatives 2.
Check for secondary causes that require correction rather than symptomatic treatment 1:
- Metabolic abnormalities: hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus 1
- Mechanical obstruction: plain abdominal X-ray can image fecal loading and exclude bowel obstruction 2
- Medication review: discontinue or adjust constipating medications when feasible 1
A complete blood count is the only routine laboratory test recommended; metabolic panels have low diagnostic utility unless other clinical features warrant them 1.
First-Line Pharmacologic Treatment
Osmotic laxatives are preferred as initial therapy 1:
- PEG 17g once daily is the most evidence-based first choice, particularly safe for elderly patients with good tolerability 2, 1
- Milk of magnesia 1 oz twice daily is an inexpensive alternative with comparable efficacy 1
- Lactulose is another osmotic option 1
Stimulant laxatives are equally appropriate as first-line therapy, especially for opioid-induced constipation 1:
Important caveat: Magnesium-based laxatives (magnesium hydroxide, magnesium citrate) should be used cautiously in renal impairment due to risk of hypermagnesemia 2, 1.
What NOT to Use First-Line
- Stool softeners (docusate): Adding docusate to senna provides no additional benefit 1
- Bulk laxatives (psyllium, methylcellulose): Not recommended for opioid-induced constipation and ineffective for medication-induced constipation without adequate hydration (at least 2 liters daily) 2, 1
- Liquid paraffin: Avoid in bed-bound patients and those with swallowing disorders due to aspiration risk 2
Special Population: Opioid-Induced Constipation
All patients receiving opioid analgesics should be prescribed a concomitant laxative prophylactically, unless contraindicated by pre-existing diarrhea 2, 1. Osmotic or stimulant laxatives are preferred over fiber 2, 1. Combined opioid/naloxone medications reduce the risk of opioid-induced constipation through phase II and III studies 2. For unresolved opioid-induced constipation, peripherally acting mu-opioid receptor antagonists (PAMORAs) may be valuable 2.
Second-Line Treatment for Refractory Constipation
If constipation persists despite first-line therapy, add a second agent 1:
- Rectal bisacodyl once daily 1
- Additional osmotic laxative (if started with stimulant) or vice versa 1
- Magnesium hydroxide or magnesium citrate (with renal function monitoring) 1
Before escalating therapy, reassess for fecal impaction or bowel obstruction 1.
Third-Line Treatment: Prokinetics
Consider metoclopramide 10-20mg orally 3-4 times daily only if gastroparesis or severe upper GI dysmotility is documented or strongly suspected 3, 1. Metoclopramide has limited efficacy for isolated constipation because it primarily affects the upper GI tract with little to no effect on colonic motility 3. This is particularly relevant for patients on GLP-1 agonists (like Mounjaro) that slow gastric emptying 1.
Do not use metoclopramide for clozapine-induced constipation due to additive dopamine antagonism increasing extrapyramidal symptom risk 3.
Fourth-Line Treatment: Secretagogues
For persistent constipation unresponsive to standard laxatives, consider newer agents 1, 4:
- Linaclotide 145 mcg once daily for chronic idiopathic constipation in adults 4
- Lubiprostone 1
- Plecanatide 1
Linaclotide demonstrated statistically significant improvement in complete spontaneous bowel movement (CSBM) responder rates (20% vs 3% placebo in one trial, 15% vs 6% in another), with improvements in stool frequency, consistency, and straining 4.
Adjunctive Non-Pharmacologic Measures
While evidence is limited, these measures support laxative therapy 2, 1:
- Privacy and comfort for normal defecation 2
- Positioning: small footstool to assist gravity and exertion 2
- Increased fluid intake: at least 2 liters daily if using fiber 1, 5
- Increased activity and mobility within patient limits 2
- Scheduled toileting: attempt defecation twice daily, usually 30 minutes after meals, straining no more than 5 minutes 2
- Abdominal massage: some evidence for efficacy in reducing gastrointestinal symptoms, particularly in patients with neurogenic problems 2
Management of Fecal Impaction
In the absence of suspected perforation or bleeding, disimpaction through digital fragmentation and extraction of stool is best practice, followed by maintenance bowel regimen to prevent recurrence 2.
Enemas are contraindicated in patients with neutropenia, thrombocytopenia, paralytic ileus, intestinal obstruction, recent colorectal/gynecological surgery, recent anal/rectal trauma, severe colitis, inflammation or infection of the abdomen, toxic megacolon, undiagnosed abdominal pain, or recent pelvic radiotherapy 2.
Elderly-Specific Considerations
Particular attention to assessment is warranted in elderly patients 2:
- Ensure toilet access, especially with decreased mobility 2
- Dietetic support for anorexia of aging and chewing difficulties that negatively influence stool volume and consistency 2
- PEG 17g/day offers efficacious and tolerable solution with good safety profile 2
- Regular monitoring of chronic kidney/heart failure when concomitant diuretics or cardiac glycosides are prescribed (risk of dehydration and electrolyte imbalances) 2
- Individualize laxatives based on cardiac and renal comorbidities and drug interactions 2
Treatment Goal
Aim for one non-forced bowel movement every 1-2 days, not necessarily daily bowel movements 1. This realistic goal prevents overtreatment and patient frustration.