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IC 1.0 > GI Drugs > Flashcards

GI Drugs Flashcards

1
Q

What is the most common secretory disorder of the GI tract?

A

acid-peptic disease

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2
Q

What disorders are included in the diagnosis of acid-peptic disease?

A
  • peptic ulcer disease
  • GERD
  • other hypersecretory states like Zollinger-Ellison syndrome
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3
Q

What are the three goals when treating acid-peptic disease?

A
  • relieved pain
  • promote healing
  • prevent recurrence
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4
Q

What two classes of drugs are available for down-regulating gastric acid secretion? Which is used more often and why?

A
  • H2 blockers are used most often because they block several pathways that promote secretion
  • anti-muscarinics are used as adjuncts to other therapies because they are relatively weak inhibitors of acid secretion
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5
Q

Which cells actually secrete gastric acid? What initiates this?

A
  • parietal cells release acid in response to histamine binding their basolateral surface
  • binding induces a rise in cAMP, which activates a H/K-ATPase on the luminal surface
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6
Q

How is gastric acid secretion regulated?

A
  • dietary peptides and parasympathetic activity active G cells in the duodenum
  • these cells release gastrin into the blood which then triggers release of histamine from ECL cells in the fundus of the stomach
  • histamine and gastrin active parietal cells, inducing acid release
  • additionally, parasympathetic activity directly stimulates parietal cells
  • acid levels rise and active D cells in the duodenum, which then release somatostatin onto G cells, impairing their release of gastrin, serving as a feedback mechanism
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7
Q

Proton Pump Inhibitors

A
  • a group of drugs that irreversibly inhibit the parietal cell H/K-ATPase, limiting gastric acid secretion
  • they are pro-drugs, inactive at neutral pH and unstable at low pH
  • as such, they are taken with food which stimulates acid release for activation and they are supplied as enteric coated granules that dissolve only at alkaline pH
  • after passing through the stomach, the enteric coating dissolves, the pro-drug is absorbed, carried to parietal cells, and accumulates in secretory canaliculi where the pH is acidic, and there, they bind the H/K-ATPases
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8
Q

Describe the activation of PPIs.

A
  • drugs ending in “-prazole”
  • the most effective drugs for suppressing gastric acid secretion
  • once daily dosing is effective at reducing acid secretion without affecting pepsin secretion or gastric motility
  • promote healing and prevent ulcer recurrence; often effective in those unresponsive to H2 agonists
  • more effective than H2 antagonists against GERD and NSAID-induced peptic ulcers
  • well-tolerated with mild side effects: GI (nausea, diarrhea, colic, flatulence), CNS (headache, dizziness), and skin rashes
  • diarrhea often occurs with prolonged use because of bacterial overgrowth at higher pH
  • they are pro-drugs, inactive at neutral pH and unstable at low pH
  • as such, they are taken with food which stimulates acid release for activation and they are supplied as enteric coated granules that dissolve only at alkaline pH
  • after passing through the stomach, the enteric coating dissolves, the pro-drug is absorbed, carried to parietal cells, and accumulates in secretory canaliculi where the pH is acidic, and there, they bind the H/K-ATPases
  • they are irreversible inhibitors, so inhibition persists after withdrawal of the drug
  • metabolized in the liver with little renal clearance
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9
Q

If PPIs are dependent on a low pH for activation, and their action is to reduce acid secretion, how do they remain effective with chronic use?

A

they function within intracellular canaliculi of parietal cells, which is upstream from the proton pump target at the luminal membrane

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10
Q

How do PPIs compare to H2 antagonists?

A
  • PPIs are usually effective when patients are unresponsive to H2 antagonists
  • PPIs are also more effective for GERD and NASI-induced peptic ulcers
  • PPIs inhibit 90-95% of acid secretion while H2 blockers inhibit 60-70% over 24 hours
  • PPIs don’t inhibit pepsin secretion, but H2 blockers do
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11
Q

H2 Receptor Antagonists

A
  • a group of drugs used to inhibit gastric acid secretion ending in the suffix “tidine”
  • they are histamine analogs that block H2 receptors on parietal cells, diminishing release of gastric acid and pepsin
  • effective at inhibiting acid secretion for up to 6 hours when OTC or 24 hours when prescription
  • most effective against nocturnal acid secretion, which is largely drive by histamine
  • given once daily at bedtime, they have a healing rate of 80-90 percent after 6-8 weeks; but declining use
  • well-absorbed, rapidly acting, well-tolerated
  • side effects include diarrhea, headaches, fatigue, myalgia, constipation, and bradycardia
  • IV administration may cause confusion, hallucinations, or agitation if patients are elderly or have renal/hepatic dysfunction
  • cimetidine has endocrine effects as well because it binds inhibits DHT binding to androgen receptors, inhibits estradiol metabolism, and increases serum prolactin; may cause gynecomastia or impotence in men, galactorrhea in women
  • famotidine > nizatidine = ranitidine > cimetidine (across a 50-fold range)
  • not given to pregnant or nursing women as they cross the placenta and enter milk
  • interferes with P450 pathways
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12
Q

How do OTC H2 blockers compare to prescription ones?

A

OTC inhibit acid secretion for up to 6 hours while prescriptions inhibit 60-70% of acid secretion over a 24 hour period

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13
Q

Which ulcers are PPI particularly effective against?

A
  • those refractory to H2 blockers

- NSAID-induced ulcers

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14
Q

H2 blockers are particularly effective against what kind of acid secretion?

A

nocturnal secretion, which is largely driven by histamine

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15
Q

What side effect of cimetidine is unique amongst the H2 blockers?

A
  • it has endocrine effects - may cause gynecomastia or impotence in men and galactorrhea in women
  • elevates serum prolactin, inhibits DHT binding to androgen receptors, and inhibits estradiol metabolism
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16
Q

How are H2 blockers used clinically? How are they prescribed?

A
  • prescribed as 1x daily dosing to be taken at bedtime

- produce ulcer healing in 80-90% of cases after six to eight weeks

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17
Q

Why is H2 blocker use declining?

A

due to discovery of PPIs and knowledge about the role H. pylori plays in peptic ulcer disease

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18
Q

Why can’t you combine PPIs with H2 blockers?

A

because the H2 blockers inhibit activation of the PPIs in parietal cell canaliculi

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19
Q

Antacids

A
  • a group of weak bases that neutralize gastric acid, forming salt and water
  • may also provide some mucosal protection by stimulating prostaglandin synthesis
  • inactivates pepsin as well
  • preparations include aluminum or magnesium hydroxide alone or in combination with sodium bicarb or a calcium slat
  • seldom used due to the advent of more convenient and effective drugs
  • antacid tablets are generally weak and needed in large numbers before having a small effect on active peptic ulcers
  • single dose given 1 hour after eating increases pH for 2 hours, second dose given 3 hours after eating extends the effect for 4 hours
  • most common adverse effects are diarrhea for magnesium and constipation for aluminum
  • may interfere with the absorption of other drugs
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20
Q

What are the most common side effects of antacids?

A
  • diarrhea for magnesium

- constipation for aluminum

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21
Q

Through what mechanism do mucosal protective agents treat peptic-acid disease?

A

they ofter a protective coating on peptic ulcers that limits exposure to acid and pepsin, which permits healing

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22
Q

What are the three primary mucosal protective agents that are used for peptic-acid disease?

A
  • sucralfate
  • misoprostol
  • bismuth subsalicylate
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23
Q

Sucralfate

A
  • a mucosal protective agents
  • polymerizes in an acid environment to produce a viscous, sticky gel that selectively binds and protects ulcer craters
  • effective in healing duodenal ulcers
  • poorly absorbed systemically, so it has few adverse effects; most common side effect is constipation
  • requires acid pH for activation and should not be given with a drug that inhibits acid secretion like PPIs or antacids
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24
Q

Misoprostol

A
  • a mucosal protective agent
  • an analog of PGE2 that binds PG receptors on parietal cells to inhibit acid secretion
  • used to prevent NSAID-induce ulcers since NSAIDs inhibit PG formation
  • most frequent side effects are diarrhea and abdominal pain
  • may cause abortion by stimulating uterine contractions
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25
Q

Bismuth Subsalicylate

A
  • aka Pepto-BIsmol
  • it is a colloidal bismuth that offers a protective coating to ulcers and is an antibacterial against H. pylori
  • minimal adverse effects but will darken tongue and stools as the bismuth sulfide forms a black solid
  • OTC use estimated at 60% of American households
  • also used for the management of infectious diarrhea by inhibiting intestinal secretions
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26
Q

H. pylori

A
  • a gram-negative bcteria
  • causes inflammatory gastritis that may lead to peptic ulcers
  • treatment requires triple therapy for 10-14 days: clarithromycin, amoxicillin, and a PPI
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27
Q

How is H. pylori treated?

A

triple therapy of:

  • clarithromycin
  • amoxicillin
  • PPI
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28
Q

What causes most gastric ulcers?

A

not acid but actually an H. pylori infection

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29
Q

On a western diet, what is a typical frequency for bowel movements?

A

at least 3 times per week

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30
Q

How is constipation defined?

A

it is a motility disorder that may refer to:

  • decreased frequency
  • difficult initiation or passage
  • passage of from or small-volume stools
  • feeling of incomplete evacuation
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31
Q

Who is likely to abuse laxatives?

A

patients with eating disorders who want to lose body weight

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32
Q

Why are laxatives usually unnecessary in the treatment of constipation?

A

because it can usually be resolved by increasing water or fiber content in the diet, appropriate bowel training, improved physical activity or exercise, and attention to psychosocial/emotional factors

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33
Q

Saline Laxatives

A
  • non-absorbable salts containing magnesium cations or phosphate anions
  • used to relieve constipation
  • being non-absorbable, they act by osmotic force to hold water inside the intestines; this distends the intestines and stimulates peristalsis
  • usually combined with a citrus juice because they have an intensely bitter taste
  • well-tolerated but avoid in those with renal insufficiency, heart disease, or electrolyte imbalance or who are using a diuretic
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34
Q

Glycerin Laxative

A
  • used to relieve constipation

- acts as a lubricant and hygroscopic agent (improves water retention in the bowel, stimulating peristalsis)

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35
Q

What do glycerin, lactulose, sorbitol, and mannitol all have in common?

A

they are non-digestible sugars and alcohols used to relieve constipation as hygroscopic agents

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36
Q

How do lactulose, sorbitol, and mannitol relieve constipation?

A
  • they are non-absorbable sugars
  • they get hydrolyzed to organic acids, acidify the luminal contents, draw water into the lumen, and increase colonic propulsive motility
37
Q

List six osmotically active laxatives.

A
  • saline laxatives (magnesium citrate or sodium phosphate)
  • glycerin
  • lactulose
  • sorbitol
  • mannitol
  • PEGylated-electrolyte solutions
38
Q

PEG-Electrolyte Solutions

A
  • osmotically active laxatives
  • poorly absorbed and retain added water by their high osmotic pressure
  • found as mixtures of sodium sulfate, sodium bicarb, sodium chloride, and potassium chloride in isotonic solution containing 60g of polyethylene glycol per liter
39
Q

What laxative is used for colonoscopy preparation?

A

3-4 liters of PEG-electrolyte solution over 3-4 hours

40
Q

How do stimulant or irritant laxatives relieve constipation?

A

they act directly on enterocytes, enteric neurons, and muscle to produce a low-grade inflammation that causes water and electrolytes to accumulate in the luminal space, increasing intestinal motility

41
Q

Bisacodyl

A
  • a diphenylmethane derivative used as an irritant laxative
  • available as an enteric coated tablet taken at bedtime to take effect the next morning
  • swallowed without chewing to avoid activation in the stomach as this might cause gastric irritation and cramping
42
Q

Ricinoleic Acid

A
  • aka castor oil
  • it is an irritant laxative that increases intestinal secretion and motility
  • seldom used because of it’s unpleasant taste and toxic potential
43
Q

Anthraquinones

A
  • irritant laxatives like aloe, cascara sagrada, or senna
  • poorly absorbed in the small intestine and activated in the colon
  • laxative effects 6-12 hours after use
  • long-term use causes melanoma pigmentation of colonic mucosa and a “cathartic colon” (dilated and ahaustral)
44
Q

What is cathartic colon?

A
  • a dilated and ahaustral colon

- commonly seen as a side effect of long-term anthraquinone use

45
Q

Bulk-Forming Laxatives

A
  • dietary supplements that add bulk and hold water to intestinal contents
  • includes methyl cellulose, lactulose, and polycarbophil
  • require drinking lots of water to maintain movement of this bulk
46
Q

Stool Softeners

A
  • agents that soften stools to facilitate expulsion
  • includes mineral oil, glycerin suppositories, and docusate sodium
  • can be given orally or rectally
47
Q

What is often prescribed to hospitalized patients to prevent straining during defecation?

A

docusate, a stool softener

48
Q

Loperamide

A
  • an anti-diarrheal that acts on intestinal opioid receptors to inhibit ACh release and decrease motility
  • 40-50 more effective than morphine for diarrhea without CNS effects
  • acts quickly (3-5 hours after ingestion) for quick relief of non-specific diarrhea
  • effective against traveler’s diarrhea but should be discontinued if clinical improvement does not occur within 48 hours (risk constipation)
  • more effective than diphenoxylate and with fewer side effects
49
Q

Difenoxin

A
  • an anti-diarrheal that acts on intestinal opioid receptors to inhibit ACh release and decrease motility
50
Q

Diphenoxylate

A
  • an anti-diarrheal that acts on intestinal opioid receptors to inhibit ACh release and decrease motility
  • less effective than loperamide
  • requires supplementation with atropine to deter abuse
51
Q

Kaolin and Pectin

A
  • essentially a chalk that absorbs compounds and binds potential intestinal toxins
  • relieves diarrhea
52
Q

Which anti-diarrheal is used for each of the following cases:

  • acute, nonspecific
  • infectious
  • traveler’s diarrhea
A
  • acute, nonspecific: loperamide
  • infectious: bismuth subsalicylate (peptobismol)
  • traveler’s: loperamide
53
Q

Somatostatin/Octreotide

A
  • antidiarrheals reserved for severe cases
  • inhibit secretion of gastrin, CCK, glucagon, GH, insulin, secretin, etc. so they’re very dirty drugs reserved for severe, refractory diarrhea
  • reduce intestinal fluid and pancreatic secretion, slow GI motility, inhibit gallbladder contraction, and reduce portal and splanchnic blood flow
54
Q

Which part of the CNS controls emesis?

A

the nucleus tractus solitarus

55
Q

What is the role of the nucleus tractus solitarus?

A

it receives lots of inputs and controls the efferent output that mediates vomiting

56
Q

Which GI disorders are controlled with H1 blockers? H2 blockers?

A
  • H1: emesis

- H2: peptic-acid disease

57
Q

H1 Antagonists

A
  • a group of anti-emetic drugs including dimenhydrinate, diphenhydramine, cyclizine, and meclizine
  • serve as H1 antagonists in the tractus solitarus
  • produce sedation and antimuscarinic activity to prevent motion sickness
58
Q

Name four groups of antagonists used in the treatment of emesis?

A
  • H1 antagonists
  • D2 antagonists
  • 5-HT3 antagonists
  • NK-1 antagonists
59
Q

Which anti-emetics are used for n/v during chemotherapy?

A

5-HT3 antagonists like ondansetron, granisetron, and dolasetron

60
Q

Metoclopramide

A

a D2 antagonists used to treat emesis

61
Q

Trimethobenzamide

A

a D2 antagonist used to treat emesis

62
Q

Ondansetron

A

a 5-HT3 antagonist used to treat emesis, particularly in those undergoing chemotherapy

63
Q

Granisetron

A

a 5-HT3 antagonist used to treat emesis, particularly in those undergoing chemotherapy

64
Q

Dolasetron

A

a 5-HT3 antagonist used to treat emesis, particularly in those undergoing chemotherapy

65
Q

Aprepitant

A

an NK-1 antagonist used to treat emesis

66
Q

Fosaprepitant

A

an NK-1 antagonist used to treat emesis

67
Q

Rolapitant

A

an NK-1 antagonist used to treat emesis

68
Q

Chlorpromazine

A

a phenothiazine used to treat emesis

69
Q

Prochlorperazine

A

a phenothiazine used to treat emesis

70
Q

Lorazepam

A

a benzodiazepine used to treat emesis

71
Q

Alprazolam

A

a benzodiazepine used to treat emesis

72
Q

THC

A

a marijuana derivative used to treat emesis through an unknown mechanism

73
Q

Dronabinol

A

a marijuana derivative used to treat emesis through an unknown mechanism

74
Q

Phenothiazines

A

a group of drugs used as anti-emetics

75
Q

Benzodiazepines

A

a group of drugs used as anti-emetics

76
Q

Pancreatic enzyme deficiencies can lead to what symptoms?

A

steatorrhea, azotorrhea, vitamin malabsorption, and weight loss

77
Q

Pancreatic Enzyme Supplements

A
  • pancreatin and pancrelipase
  • administered with each meal and snack
  • replace pancreatic enzyme deficiencies
  • can lead to hyperuricosuria and renal stones because of their high purine content
78
Q

Orlistat

A
  • a newer anti-obesity medication
  • works in the gut by blocking GI lipase, thereby reducing absorption of fats
  • may cause flatulence, steatorrhea, and fecal incontinence
79
Q

Sibutramine

A
  • a newer anti-obesity medication
  • works as a SERT/NET inhibitor in the CNS to reduce appetite
  • may cause tachycardia or hypertension
80
Q

Rimonabant

A
  • a newer anti-obesity medication
  • works as a CB1 receptor antagonist in the CNS to reduce appetite
  • may cause depression, anxiety, or nausea
81
Q

TCAs

A
  • antidepressants that at low doses can be used to treat the abdominal pain associated with IBS
  • use amitriptyline or desipramine
82
Q

Amitriptyline

A

an antidepressant that at low doses can be used to treat the abdominal pain associated with IBS

83
Q

Desipramine

A

an antidepressant that at low doses can be used to treat the abdominal pain associated with IBS

84
Q

Dicyclomine

A

an anticholinergic used as an antispasmodic in the treatment of IBS

85
Q

Hyoscyamine

A

an anticholinergic used as an antispasmodic in the treatment of IBS

86
Q

Tegaserod

A
  • a partial 5-HT4 agonist
  • used in the emergent treatment of IBS
  • limited by serious cardiovascular events
87
Q

Alosetron

A
  • a 5-HT3 antagonist used in the treatment of IBD when conventional therapy has failed
  • best for diarrhea-predominant IBS
  • risk of serious cardiovascular events
88
Q

Eluxadoline

A
  • a kappa opioid receptor agonist and delta opioid receptor antagonist
  • used in the treatment of diarrhea-predominant IBS
  • reduces neuronal drive on peristalsis
  • may cause spasm in the sphincter of Oddi, resulting in pancreatitis
89
Q

Rifaximin

A
  • an antibiotic used to treat diarrhea-predominant IBS
  • similar to rifampin
  • may alter bacterial content of GI tract

IC 1.0 (24 decks)

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