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Flashcards in Lower GI pharmacology Deck (26)
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How can Constipation happen?

• Decreased GI motility
• Or excess fluid removal and thus fecal thickening or congealing


Inspissated = ?

Inspissated = thickened or congealed


How might diarrhea happen?

• Increased GI motility
• Or increased osmotic load in intestine
• Or increased secretion of water and electrolytes into intestine and now colon can't reabsorb it all
○ Or a combo of these processes
• This allows us to categorize into different groups


What OTHER drugs have constipation as a side effect?
• These can be used, in theory, as drugs for diarrhea OR you might need to combine laxative therapy with these drugs

• Calcium channel blockers
○ Verapamil
• Opioid analgesics
• Antimuscarinics
○ Or drugs with antimuscarinic side effects
○ TCAs, antipsychotics, 1st generation antihistamines, parkinsonian agents
• Aluminum and calcium containing antacids plus calcium supplemnts
○ Especially calcium carbonate
• Chemotherapeutic vinca alkaloids


How is constipation treated chronically?

• Lifestyle
○ Higher fiber
○ Higher movement, especially abdominal muscles
○ Adequate fluid intake
• Laxatives are really only used for acute management


What are the bulk-forming laxatives?

• Psyllium
• Methylcellulose
○ Leads to swelling of stool and distension of colon


What are the saline/osmotic laxatives?

• Magnesium hydroxide
• Lactulose
○ Increases fluid volume in colon


What are the wetting agent laxatives?

• Docusate
• Mineral oil
○ These moisten the stool to ease passage


What are the stimulant/irritant laxatives?

• Bisacodyl
• Senna
○ Stimulate enteric nerves to increase GI motility


Why are fiber/bulk-forming laxatives supposed to be tried first?

• They most closely approximate the natural way of stimulating defecation
○ Facilitate passage and stimulate perisalsis via absorption of water and subsequent bulk expansion
• Effective in 12-24 hours to 3 days
○ Take with 8oz water or juice
• Safe to combine with other drugs
• Psyllium and methylcellulose


What are the osmotically active laxatives and when are they used?

• Milk of magnesia or magnesium citrate
○ Mild to moderate constipation
○ Avoid in renal dysfunction
• Phosphate enemas
○ Reserve this for fecal compaction
• Polyethylene glycol (PEG) (with electrolyte solution)
○ High volume solutions
§ 4L of golytely or colyte
§ Bowel cleansing prior to radiologic, surgical or endoscopic procedures
§ Sodium and potassium salts to prevent net transfer of electrolytes into lumen
○ Smaller volume solutions
§ 250-500mL of miralax
§ Refractory constipation
§ Daily dose for 2 weeks or less duration
§ Prolonged use can lead to electrolyte depletion (also watch for bulemia and abuse)
• Lactulose
○ Dissacharide metabolized by colonic bacteria to low molecular weight acids leading to osmotic diarrhea and increased colonic peristalsis
○ Useful in elderly, used in acute situations


Which osmotically active agents should you avoid in renal failure?

• Mg salts, can lead to hypermagnesemia


What is the most widely abused class of laxatives?

• Bisacodyl (stimulant or irritant)
• Has electrolyte and fluid deficiencies as most severe side effect or consequence


What laxative agent would you use in a patient with cardiovascular disease, hernia, or postpartum patients?

• A stool softener
○ Stool-wetting and emollient agents
• Surfactant (docusate)
• Lubricant (mineral oil/olive oil)
○ Helps things move along


Methylnaltrexone and naloxegol are examples of what type of drug? When might you use these?

• Peripherally acting opioid antagonists
• In patients on chronic opioids for non-cancer pain that need laxatives
• These are designed to NOT mess with the opioid analgesia at all, but just keep the opioids from lowering GI motility


What OTHER drugs have diarrhea as their side effects?

• Colchicine
• Digoxin
• Misoprostol
• Antibiotics (especially broad spectrum)
• Muscarinic agonists


While most diarrhea is self-limiting, when and in whom are you worried about severe complications?

• Infants, children, elderly.
• Concern here is fluid loss, electrolyte imbalances and hypotension
• Oral rehydration therapy is the mainstay here. Remember that most treatments for diarrhea are symptomatic, not targeting the pathophys


What are the opioids you can use for antidiarrheal therapy?

• Paregoric
• Opium powder
• Diphenoxylate + atropine = Lomotil
• Loperamide = imodium


What can go wrong with using opioids to manage diarrhea?

• We are talking about the peripherally acting ones here
• They have low addiction potential b/c of poor BBB crossing
• They can lead to CNS depression in children
• Also can lead to paralytic ileus
• Can worsen shigella infections


What opioid receptors are implicated in diarrhea?

• Mu - motility
• Delta - intestinal secretion
• Mu and delta together - absorption
• Loperamide has anti-secretory capacity in cholera toxin infection


What are the absorbent anti-diarrheals?

• Kaolin
• Pectin
• Attapulgite
• Charcoal
• Bismuth subsalicylate (pepto bismol)


What is important to think about with bismuth subsalicylate use?

• Don't use bismuth subsalicylate in children under 12
○ Salicylate risk for reye's syndrome
Reye's (Ryes) syndrome is a rare but serious condition that causes swelling in the liver and brain. 


What is the rationale behind using adsorbent anti-diarrheals?

• Adsorb toxins that cause irritation (meh)
• Can adsorb drugs, nutrients, digestive enzymes too
• Take after each loose bowel movement until symptoms are controlled
• Use in mild to moderate diarrhea
• Don't use bismuth subsalicylate in children under 12
○ Salicylate risk for reye's syndrome


Why would somebody with IBS be prescribed TCAs?

• Not for any association with depression or anxiety
• Apparently low dose TCAs help treat symptomatic abdominal pain and discomfort


What is alosetron?

• IBS medication - serotonin 5-HT3 antagonist
• Block of 5-HT3 receptor on sensory and motor neurons reduces pain and inhibits colonic motility
• Extensive P450 metabolism (doesn't induce, but is metabolized by that system)
• Main side effect to worry about is ischemic colitis in 3/1000 patients
• Only use in women with IBS that has diarrhea as the only presenting symptom and is refractory to other treatments. Even then 1/2 patients find relief


What is Tegaserod?

• 5-HT4 agonist (pay attention)
• IBS treatment in particular for constipation
• Leads to release of NT involved in peristaltic reflex promoting gastric emptying and intestinal motility
• Renal secretion and hepatic metabolism
• Used in women below 55 with predominant constipation or chronic idiopathic constipation