Lower GI pharm Flashcards
Drugs with constipation as a side effect
Ca channel blockers (verapamil), opioid analgesics, antimuscarinics, drugs with antimuscarinic side effects (TCADs, antipsychotics, 1st gen antihistamines, parkinsonian agents), Al and Ca-containing antacids, chemotherapeutic vinca alkaloids
Primary use of laxatives
treatment of acute constipation
Treatment of most simple constipation
high fiber diet, exercise (abs), adequate fluid intake
First line for constipation
fiber/bulk-forming laxatives like psyllium (Metamucil)
Psyllium mechanism of action
facilitate passage and stimulates peristalsis via absorption of water and subsequent bulk expansion
Psyllium interactions
digoxin and salicylates
preferred adjunct to fiber in treatment of constipation
saline (osmotically active agents) cathartics
Mechanism of saline cathartics
nonabsorbable ions –> osmotic retention of water in intestine –> increased peristalsis
Milk of Magnesia contraindications
renal dysfunction (can lead to increased Mg retention
Use of phosphate enemas
fecal impaction
Miralax use
difficult to treat constipation
prolonged use –> electrolyte depletion
Lactulose mechanism
nondigestable sugar dissacharide –> metabolized by colonic bacteria to low molecular weight acid –> osmotic diarhea, increased colonic peristalsis
Lactulose use
acute constipation in elderly patients
Bisacodyl (Dulcolax) mechanism
activation of prostaglandin-cAMP and NO-cGMP pathways –> induced low-grade inflammation in bowel –> accumulation of water and electrolytes –> stimulation of peristalsis
Bisacodyl ADRs
electrolyte/fluid deficiencies, severe cramping
most widely abused laxative
Docusate mechanism
it is a surfactant –> stool softener (facilitates admixture of aqueous and fatty substances)
Docusate use
prevention of constipation in combination with stimulant laxative (Bisacodyl) when initiating opioid analgesic therapy
Glycerin suppositories use
initiate defecation reflex in neonates/peds
Peripherally acting opioid antagonists
Methylnaltrexone, naloxegol
used for patients taking opioids for non-cancer pain that have failed laxative therapy
Drugs associated with diarrhea
misoprostol, antibiotics (esp broad spec), muscarinic agonists, SSRIs, colchicine, NSAIDs, digoxin
Management of sudden onset of diarrhea
usually self-limiting
opioid antidiarrheals
diphenoxylate, loperimide
Loperimide use
traveler’s diarrhea, cholera
should be discontinued if no improvement in 48h
Polycarbophil (Mitrolan) mechanism
marked capacity to bind free fecal water
Polycarbophil use
diarrhea (binds water) and constipation (prevents fecal dessication)
bismuth subsalicylate (Pepto Bismol, Kaopectate) use
mild/moderate diarrhea (promotes formed stool)
bismuth subsalicylate contraindications
Children under 12 (risk of Reye’s syndrome)
Probiotics mechanism
suppress growth of pathogenic organisms, restoring normal flora
IBS pathophysiology
idiopathic, chronic, relapsing abd discomfort and altered GI motility
Treatment of IBS
low dose TCADs for abd pain/discomfort
antidiarrheals/fiber/laxatives for improving bowel function
Agents specific for IBS: 5-HT3 antagonists (Alosetron), 5-HT4 agonists (Tegaserod)
Alosetron mechanism
blocks 5-HT3 receptors on sensory/motor neurons –> reduced pain and inhibits colonic motility
Alosetron use
Only in severe IBS in women with diarrhea as the prominent symptom, unresponsive to conventional therapy
Alosetron ADRs
constipation, ischemic colitis (1/3000)
Tegaserod mechanism
5-HT4 agonist –> release of neurotransmitters for peristaltic reflex –> gastric emptying and intestinal motility
Tegaserod contraindications
renal or hepatic dysfunction
Tegaserod use
women under 55 with IBS and predominant constipation; chronic idiopathic constipation that is unresponsive to other treatments
Tegaserod ADRs
linked with heart attacks, strokes, unstable angina
