Constipation Medications: 5 Pearls Segment

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1. Pearl 1: High Yield Reversible Causes and Complications of Constipation
   1. There are two types of constipation: 
      1. Primary constipation/Chronic idiopathic constipation: diagnosed using the Rome IV criteria 
         1. Patients must have two or more of the following for the last 3 months with symptom onset at least 6 months prior to diagnosis:
            1. Straining during more than ¼ (25%) of defecations
            2. Lumpy or hard stools more than ¼ (25%) of defecations
            3. Sensation of incomplete evacuation more than ¼ (25%) of defecations
            4. Sensation of anorectal obstruction/blockage more than ¼ (25%) of defecations
            5. Manual maneuvers to facilitate more than ¼ (25%) of defecations (e.g., digital evacuation, support of the pelvic floor)
            6. Fewer than three SBM per week
            7. Loose stools are rarely present without the use of laxatives
            8. Insufficient criteria for irritable bowel syndrome
      2. Secondary constipation: which can be remembered using the mnemonic LMNOP
   2. Lifestyle: 
      1. Patients who are bedbound or immobile, those with eating disorders and those with low fiber and water intake are at a higher risk of constipation
   3. Metabolic: 
      1. Hypercalcemia, hypokalemia, hypomagnesemia and hypothyroidism can contribute to constipation
   4. Neurologic: 
      1. Ensure that patients with neurologic dysfunction (e.g. spinal cord defects, history of CVA, dementia, Parkinson disease, multiple sclerosis) have aggressive bowel regimens on admission
   5. Obstructive
      1. Consider structural causes of constipation including anal or intestinal strictures and obstructive tumors
   6. Pharmacologic
      1. Prescribed medications which are common offenders are antipsychotics, anticholinergics, narcotics, calcium channel blockers, tricyclic antidepressants
      2. Over-the-counter medications including iron supplements, aluminum containing drugs, calcium supplements, antacids and antihistamines
2. Pearl 2: Deep Dive into Fiber, Hydration and Bulk-Forming Laxatives
   1. Fruits vs Psyllium
      1. Dried plums or prunes have been shown to be more effective for reducing constipation that psyllium 
      2. Kiwi may slightly increase stool frequency compared to psyllium
   2. Fiber Supplementation (Psyllium, methylcellulose)
      1. Mode of action: increases stool weight which can reduce transit time, increase water collection and bacterial mass from fermentation
      2. Although there is evidence showing that soluble fibers (E.g. psyllium, inulin, oatmeal) improve constipation, the evidence for insoluble fiber (E.g. wheat bran) is inconsistent.  
      3. Psyllium should be taken at least 2 hours before or after other medications (e.g. levothyroxine, calcium supplements, zinc supplements) as it can reduce their absorption
   3. Hydration 
      1. There is no benefit of increased hydration in patients who are adequately hydrated
3. Pearl 3: Osmotic and Stimulant Laxatives
   1. Osmotic laxatives 
      1. Mode of action: draws fluid into the lumen of the bowels through osmosis
      2. Time of onset: 
         1. Lactulose: 24-48 hours
         2. Magnesium citrate: 0.5-6 hours
         3. Magnesium oxide: 3-6 hours
         4. Polyethylene glycol: up to 72 hours
      3. Side effects and considerations 
         1. Magnesium oxide can be used in patients with renal impairment, but keep an eye on the magnesium level. 
         2. Lactulose can cause more bloating and cramping 
   2. Stimulant laxatives:
      1. Mode of action: direct stimulation of colonic neurons 
      2. Time of onset: up to 6-12 hours and used as a rescue laxative
      3. Side effects and considerations
         1. There is no good evidence of their efficacy after more than four weeks 
         2. Studies have shown that stimulant laxatives do NOT damage the enteric nervous system
         3. Tolerance to stimulant laxatives is uncommon.
4. Pearl 4: Suppositories and Enemas
   1. Suppository vs enema 
      1. A suppository is a small solid capsule and an enema is a liquid medication
   2. Types of enemas 
      1. Osmotic enemas: sodium phosphate enema, glycerine enema, lactulose enema
      2. Lubricating enemas: mineral oil enema
      3. Hypotonic enemas: tap water enema, soap sud enema
   3. Considerations
      1. Sodium phosphate enemas can cause electrolyte abnormalities, especially in elderly patients and those with renal dysfunction 
      2. Mineral oil enemas require patient retention
      3. Discuss what is most comfortable for the patient
      4. Discuss timing and preparation with your nursing colleagues
5. Pearl 5: Opioid Induced Constipation
   1. Mode of action of opioids: act on the mu opioid receptors which cause inhibition of GI motility and water secretion and absorption in the GI tract resulting in constipation. 
   2. Transdermal formulations of opioids are shown to have less incidences of opioids induced constipation in comparison to oral
   3. Peripherally acting mu opioid receptor antagonists (PAMORAs)
      1. Mode of action: blocks the actions of opioids in the gut but do not affect pain control 
      2. It is recommended to stop treatment with other maintenance laxatives prior to starting PAMORAs
      3. Side effects: abdominal pain, diarrhea, nausea

Contributors

Shreya Trivedi, MD, ACP Member – Host, Editor
Kalaila Pais, MD – Host, Editor
Allen Lee, MD – Guest*
Taylor Thompson, PharmD - Guest
Jack Sibilia, RN - Guest

Reviewers

Adam Strauss, MD
Brian Persaud, MD

* Allen Lee, MD – Consultant – GSK

Those named above, unless otherwise indicated, have no relevant financial relationships to disclose with ineligible companies whose primary business is producing, marketing, selling, re-selling, or distributing healthcare products used by or on patients.  All relevant relationships have been mitigated.

Release Date:  April 30, 2025

Expiration Date: April 29, 2028

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