GI drugs
	For Flash! users, split this file into 3 separate memos at the obvious locations


PEPTIC ULCER DRUGS

4 mechanisms of actions
	
	acid neutralization
	acid reduction
	protect mucosal barrier
	eradicate HP

Antacids
	
	Al(OH)3, Mg(OH)2, CaCO3
	MOA: HCl neutralization (also pepsin inactivation, bind bile salts)
	Rx duodenal ulcers, GERD; stress ulcer prophylaxis
	PK: frequent administration req'd, dec bioavailability of other drugs
	Tox: belching, diarrhea, constipation (Al), cation absorption

-tidine
	
	cimetidine (tagamet), ranitidine (zantac), famotidine (pepcid), nizatidine (axid)
	MOA: histamine H2-R antagonist
	Rx GERD, duodenal & gastric ulcers; duodenal ulcer prophylaxis
	PK: P450 interactions
	Tox: CNS confusion, somnolence, gynecomastia

-prazole
	
	omeprazole (prilosec), esomeprazole (nexium), lansoprazole (prevacid), rabeprazole, pantoprazole
	MOA: proton pump inhibitors (sulfenamide irrev inhibition of H/K-ATPase)
	Most potent acid reduction drug
	Rx peptic ulcers (2nd line after H2A), GERD erosive esophagitis, ZES
	PK: C-P450 interactions, short t1/2 but long lasting effect
	Tox: bacterial overgrowth of small bowel

Sucralfate (carafate TM)
	
	MOA: sulfated polysaccharide (gel that binds +ve proteins in ulcers, also inhibits pepsin)
	Rx peptic ulcer, bile reflux; stress ulcer prophylaxis
	PK: dec bioavailability of other drugs
	Tox: constipation (contains Al)

Misoprostol
	
	MOA: prostaglandin E1 analog -> dec gastric acid secretion & inc mucus and HCO3 secretion
	Gastric ulcer prophylaxis in setting of chronic NSAIDs
	Tox: uterine contractions, diarrhea, abdominal cramps

H. Pylori treatment
	
	2 Abx (amoxicillin & clarithomycin) + acid suppression (H2A or PPI)
	Resistance is rising


GASTRIC MOTILITY DRUGS

MOAs for gastric motility
	
	Cholinergic or NANC agonists
	Dopamine antagonists

MOAs for nausea/vomiting
	
	Vomiting: block 5HT3, ACh, histamine, or BDZ receptors
	Motion sickness: histamine or ACh blockers

Metoclopramide (reglan TM)
	
	MOA: {cholinergic & 5HT4 agonist, DA blocker} -> inc motility, inc LES tone, antiemetic
	Rx gastroparesis, GERD, nausea/vomiting
	Tox: somnolence, nervousness, parkinsonism, tardive dyskinesia

Ondansetron (zofran TM)
	
	MOA: CNS 5HT blocker
	Rx nausea of many types but not motion sickness; Rx pregnancy hyperemesis
	Expensive
	Tox: well tolerated

Phenothiazines
	
	prochlorperazine, chlorpromazine
	MOA: dopamine blocker at CTZ
	Rx motion sickness

Domperidone
	
	MOA: dopamine blocker at CTZ
	Rx gastroparesis, nausea/vomitinq

Antihistamines
	
	MOA: H1 receptor blocker at CTZ
	Rx motion sickness, post-op emesis

Anticholinergic
	
	scopolamine
	MOA: muscarinic blocker at CTZ
	Rx motion sickness

Cannabinoids
	
	dronabinol
	MOA: details unclear, involves cannabinoid receptor
	Rx vomiting, appetite stimulant
	Expensive



DIARRHEA/CONSTIPATION

Hydroscopic agents
	
	psyllium (metamucil), polycarbophil (fibercon), carboxymethylcellulose (citrucel), kaolin clay & pectin (kaopectate)
	MOA: absorb excess water (Rx diarrhea) or hold water in lumen (Rx constipation)

Cholestyramine (questran TM)
	
	MOA: bile salt binders -> dec colon secretion
	Rx diarrhea

Bismuth salicylate (peptobismol TM)
	
	MOA: details unclear (antisecretory, anti-inflamm, anti-bacterial)
	Rx diarrhea

Opioids
	
	loperamide (imodium), difenoxin + atropine (motofen), diphenoxylate + atropine (lomitil)
	MOA: inc fluid abs, dec fluid secretion & motility
	Rx diarrhea
	Tox: overdose (sedation, ileus paralysis)

Emollients
	
	docusate sodium (colace)
	MOA: anionic detergent (inc water and fat in stool)

Mg salts
	
	MOA: hypertonic soln draws water into lumen

"Stimulant" cathartics
	
	Ricinoleic acid (castor oil)
	MOA: induce low-grade inflamm in small bowel & colon -> inc water secretion
	Tox: reversible melanosis coli, "cathartic colon" due to chronic abuse

Nonabsorbable sugars
	
	MOA: osmotic effect to hold water in lumen