Constipation Flashcards
Name examples of bulk-forming laxatives that are (1) natural plant products/fibres; (2) Semi-synthetic plant fibres; and (3) Synthetic fibres
Examples of bulk-forming laxatives that are:
(1) Natural plant products/fibres: Psyllium, Sterculia, Agar, Bran
(2) Semi-synthetic plant fibres: Methylcellulose
(3) Synthetic fibres: Polycarbophil
Briefly explain the mechanism of action of bulk-forming laxatives
Indigestible, hydrophilic colloids (fibre)
Absorb water and form bulk, emollient gel that distends colon (increases stool mass)
Promotes peristalsis
What are the most common adverse effects/concerns with bulk-forming laxatives?
Bacterial digestion of plant fibres within the colon may lead to flatus, bloating and abdominal pain
Avoid if an obstruction is suspected
Interaction with the absorption of other drugs
List examples of (1) sugar, (2) salt, and (3) balanced osmotic laxatives.
Examples of osmotic laxatives:
(1) Nonabsorbable Sugars: Sorbitol, lactulose
(2) Nonabsorbable Salts: Magnesium hydroxide (milk of magnesia); Magnesium citrate; Sodium phosphate
(3) Balanced: Balanced Polyethylene Glycol (PEG)
* Balanced, isotonic solution of osmotically active sugar (PEG) and various salts
Briefly explain the mechanisms of action of osmotic laxatives.
Osmotically-mediated water movement into the bowel increases stool liquidity (softer stool) and volume
Increased volume stimulates peristalsis
High doses can produce bowel evacuation (purgation) within 1 to 3 hours
What is the MOST IMPORTANT advice for a patient prescribed an osmotic laxative?
Maintain adequate hydration by increasing oral fluid intake
What are the major concerns/adverse effects of osmotic laxatives?
- Colonic bacteria act on sugars → severe flatus & abdominal cramps
Note that PEG although an osmotically active sugar does not produce significant cramps or flatus.
Important to maintain adequate hydration by increasing oral fluid intake.
Sodium phosphate can cause:
Hyperphosphataemia, hypernatraemia and hypocalcaemia, hypokalaemia.
Normally not clinically significant but may cause cardiac arrhythmias or acute renal failure due to tubular deposition of calcium phosphate (nephrocalcinosis).
Should not be used in patients who are frail, elderly, on diuretics, unable to maintain adequate hydration or who have renal insufficiency or cardiac disease.
Explain whether lactulose osmotic laxatives are safe for patients with (1) lactose intolerance; or (2) diabetes mellitus.
Lactulose itself does not pose a risk to patients with lactose intolerance or diabetes mellitus.
But caution is necessary as due to the manufacturing process, lactulose osmotic laxative formulations often contain carbohydrate impurities including galactose, lactose, and other sugars (e.g., epilactose, tagatose, and fructose).
Lactose poses a risk to patients with lactose intolerance
Sugars such as galactose, lactose, and fructose may affect blood glucose levels in patients with diabetes mellitus. However, studies of blood sugar levels following administration of lactulose formulations known to contain carbohydrate impurities have found only minor or no significant changes in blood sugar levels.
Name examples of (1) natural product anthraquinone derivative and (2) synthetic diphenylmethane derivative stimulant or cathartic laxatives. State routes of administration and how fast these drugs act.
Examples of stimulant or cathartic laxatives:
(1) Natural product, Anthraquinone Derivatives:
Aloe, Senna and Cascara (oral or per rectum)
Produce bowel movements in 6 to 12 hrs (oral) or 2 hrs (rectal)
(2) Synthetic, Diphenylmethane Derivatives
Bisacodyl (oral or per rectum)
Tablet or rectal suppository
Induces bowel movement in 6-10 hours (oral) or 30-60 minutes (rectal)
Used in conjunction with PEG for colonic cleansing prior to colonoscopy
Explain whether stimulant or cathartic laxatives (1) cause dependence, (2) cause colon cancer or (3) cause cardiac toxicity.
These are all concerns that patients who have searched online may ask about. But none are evidence-based medicine concerns.
(1) Long-term use may be required in patients who are neurologically impaired or bed-bound. This led to concerns that chronic use may lead to dependence and destruction of the myenteric plexus resulting in colonic atony and dilation. However, more recent systematic reviews and meta-analyses do not support this concern.
(2) Chronic use of anthraquinone derivatives leads to brown pigmentation of the colon (melanosis coli). This led to concern regarding carcinogenesis, but epidemiological studies do not support an association with colorectal cancer.
(3) An early diphenylmethane derivative, phenolphthalein, was withdrawn due to cardiac toxicity. However, bisacodyl appears to be safe.
To which class of drugs does lubiprostone belong?
Chloride channel activator laxatives
Briefly explain the mechanisms of action of lubiprostone.
Lubiprostone:
Is a bicyclic fatty acid derived from prostaglandin E1
Stimulates type 2 chloride channels (ClC-2) in the small intestine
Increases chloride-rich fluid secretions, and water follows the chloride osmotically
Stimulates motility and shortens intestinal transit time due to increased stool volume and liquidity
What are the most significant adverse effects of lubiprostone?
Nausea due to delayed gastric emptying (approx. 30 % of patients)
Also stomach/abdominal pain,dizziness, headache, diarrhoea
List the TWO indications for lubiprostone.
Lubiprostone is used to treat:
chronic idiopathic constipation
irritable bowel syndrome with constipation
constipation caused by opioid medications (other than diphenylheptane opioids e.g., methadone) in people with ongoing pain due to medical conditions other than cancer.
Name a drug indicated as a laxative only to reverse opioid-induced constipation. Briefly, explain how this drug is used and administered.
Methylnaltrexone
Treat constipation caused by opioids in adults with chronic pain (e.g., patients receiving palliative care)
Administered subcutaneously once daily or every 2 days
