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MODHIII - Unit 3 > GI Drugs > Flashcards

GI Drugs Flashcards

1
Q

Routes of acid stimulation

A
  • histamine: from ECL cells
  • gastrin: from G cells
  • acetylcholine: nervous system (vagus nerve)
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2
Q

Histamine stimulated acid release is inhibited by

A

protanoids

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3
Q

Histamine acts on what receptor on parietal cell

A

H2

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4
Q

How is acid pumped into the stomach from parietal cells

A

K+/H+ ATPase antiporter

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5
Q

Proton Pump Inhibitors (PPIs): drugs

A
  • Omeprazole
  • Esomeprazole
  • Lansoprazole
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6
Q

PPIs activation

A
  • all are prodrugs that require acid activation
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7
Q

PPIs: action

A
  • IRREVERSIBLY inhibit the proton pump
  • enter parietal cells from the systemic circulation & activated withing the acidic environment around proton pump
  • ineffective if activated in stomach by acid so they are put in gelatin capsules, coated, mixed with bicarb, or given parenterally
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8
Q

PPIs: administration

A
  • gelatin capsules (omeprazole, esomperazole, lasoprazole)
  • enteric coated tablets (pantoprazole, rabeprazole, omeprazole)
  • mixed w/ bicarb (omeprazole)
  • pantoprazole and lansoprazole can be give parenterally
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9
Q

PPIs: dose

A
  • dosed daily

- active for about 2 hours but therapy relies on slow turnover of K+/H+ ATPase at the apical surface

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10
Q

PPIs: uses

A
  • lower acid secretion 90%
  • GERD, erosive esophagitis, peptic ulcers, zollinger-ellison syndrome, NSAID induced gastric ulcers, part of H. pylori treatment
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11
Q

PPIs: clearance

A

LIVER

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12
Q

PPIs: activity of proton pumps

A
  • not all proton pumps are active at any one time
  • only those that are active react with these drugs
  • treatment requires 2-5 days
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13
Q

PPIs: adverse reactions

A
  • nausea, abdominal pain, constipation, flatulence, diarrhea
  • drug interactions through altered CYP activity: increase serum WARFARIN concentrations, decrease activation of clopidogrel
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14
Q

H2 receptor antagonists: drugs & duration

A
  • cimetidine: 4-5 hrs
  • ranitidine: 6-8 hrs
  • famotidine: 10-12 hrs
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15
Q

H2 receptor antagonists: process and use

A
  • block base level of acid secretion maintained by ECL cells

- use: NOCTURNAL acid secretion, duodenal ulcers, zollinger-ellison

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16
Q

H2 receptor antagonists: effectiveness

A
  • decrease acid secretion 70% for 24 hours with daily dosing
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17
Q

H2 receptor antagonists: excretion

A
  • RENAL via organic cation system
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18
Q

H2 receptor antagonists: adverse reactions

A

-

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19
Q

H2 receptor antagonists: adverse effects of cimetidine

A
  • long term use of cimetidine at high doses decreases testosterone binding to androgen receptor and hydroxylation of estradiol causing galactorrhea in women and decreased sperm count, impotence and gynecomastia in men
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20
Q

H2 receptor antagonists: tolerance

A
  • tolerance can develop in 3 days due to direct acid stimulation by gastrin
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21
Q

Prostaglandin analogs: Misoprostol

A
  • synthetic analog of PGE1
  • short acting, up to 3 hrs
  • use: NSAID induced injury (less than PPIs and H2 antagonists though)
  • adverse: diarrhea (30%), exacerbate IBD, increase uterine contractions
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22
Q

Sucralfate

A
  • octasulfate of sucrose with Al(OH)3
  • forms sticky neutral pH polymer coating that covers epithelium
  • uses: stress ulcers (sticks better to duodenal than gastric ulcers)
  • ACID activated, so take before food, and avoid antacids and PPIs
  • adverse: constipation, block absorption of other drugs through stomach
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23
Q

Antacids: process & components

A
  • neutralize pH of gastric contents

- Al(OH)3, Mg(OH)2, CaCO3 common components

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24
Q

Antacids: action

A
  • fast acting: 15 min

- last up to 2-3 hours WITH food

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25
Q

Antacids: Mg vs. AL

A

Mg: fast acting, stimulates gastric emptying and motility
Al: slower acting, delays gastric emptying and slows motility

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26
Q

Antacids: gas

A
  • surfactant simethicone is sometimes added to reduce gas
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27
Q

Antacids: adverse effects

A
  • rebound acid secretion
  • Mg contraindicated in RENAL disease
  • interference with GI absorption of other drugs: take antacids 2 hrs before or after other drugs**
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28
Q

Muscarinic antagonists

A
  • pirenzepine: selective for M1 receptors
  • blocks neurotransmission in ganglia resulting in less vagal stimulation of parietal and ECL cells
  • reduce basal acid by 50%
  • significant anticholinergic side effects
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29
Q

H. pylori infection

A
  • 50% of all humans: 1/3 are pathogenic, difference is vacuolating endotoxin A
  • associated with over half of peptic ulcer disease, gastritis, GERD
  • bacteria need acid, which activates the toxin
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30
Q

H. pylori treatment

A
  • combination of acid neutralization, cytoprotection, antibacterial agent
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31
Q

Gastrointestinal motility: process

A
  • mechanical/chemical stimulation leads to serotonin release from enterochromaffin cells that stimulate primary afferent neurons
  • ACh stimulates constriction (ORALLY), NO stimulates relaxation (ANALLY)
  • uses myenteric plexus control of circular muscle
32
Q

Tegaserod

A
  • serotonin partial agonist

- used for females with irritable bowel syndrome

33
Q

Cisparide

A
  • 5-HT4 receptor agonist and adenylate cyclase stimulant

- used for GERD and gastroparesis

34
Q

Adverse reactions of tegaserod & cisapride

A
  • fatal cardiac arrhythmias

- only available through restricted distribution programs administered by FDA or manufacturer

35
Q

Bethanechol

A
  • cholinergic derivative
  • used to help urination in post surgical patients
  • aim is to selectively activate M2 and M3
  • side effects: bradycardia, flushing, diarrhea, cramps, salivation, blurred vision
36
Q

Neostigmine methylsulfate

A
  • acetylcholinesterase inhibitor

- used to counter an ILEUS

37
Q

Metoclopramide

A
  • dopamine receptor antagonists (enhance normal ACh response)
  • increases LES tone and upper GI motility
  • can relieve symptoms of GERD but does not promote healing
  • uses: nausea, vomiting in dysmotility syndromes and as an antiemetic
    adverse: extrapyramidal effects, dystonias, parkinson like symptoms, tardive dyskenesia with chronic use
38
Q

Motilin activity

A
  • motilin is a peptide hormone that amplifies motor activity through effects on enteric neurons and smooth muscle
  • secreted by enterochromaffin cells and M cells in upper small bowel
39
Q

Erythromycin and other “mycin’s”

A
  • imitate motilin
  • macrolide antibiotics
  • cause gastric dumping which can move bezoars, improve gastric emptying with ileus, scleroderma, pseudo-obstructions
  • fast dumps can be painful, no recommended for chronic use
40
Q

When is diarrhea necessary

A
  • cholera and shigellosis
41
Q

Laxation

A
  • evacuation of formed fecal material from the rectum
42
Q

Catharsis

A
  • uniform evacuation of material from the entire colon (watery
  • many cathartics produce laxation at low dosages
43
Q

Mechanisms of laxatives

A
  • prokinetic agents
  • bulk forming agents increase mechanical efficiency
  • wetting agents, osmotic, irritants
44
Q

Osmotic laxatives: process

A
  • non absorbable agents
  • cause water retention
  • really cathartics causing bowel emptying with watery stool, but act as laxatives at lower dosage
45
Q

Osmotic laxatives: types

A
  • alcohols: polyethylene glycol (mcdonalds shakes)
  • salts: magnesium hydroxide (Milk of Magnesia), other Mg salts
  • sugars: lactulose, sorbitol, mannitol
46
Q

Osmotic laxatives: Mg

A
  • may stimulate CCK receptors and increase motility
  • should be avoided in individuals with renal insufficiency, cardiac disease, electrolyte abnormalities, or with diuretic use
47
Q

Osmotic laxatives: sugars

A
  • lactulose, sorbitol, mannitol
  • used for constipation with opioid use and vincristine
  • bacterial fermentation of lactulose also drops luminal pH and can trap NH4 (increased in colon of patients with severe hepatic disease)
48
Q

Glycerin

A
  • suppository that acts as a hydroscopic agent and lubricant
  • increase water retention stimulates peristalsis producing evacuation reflex
  • rectal administration can produce a bowel movement within an hour
49
Q

Stool wetting agents

A
  • docusate salts
  • surfactants that allow mixing of fatty substances and water in stool
  • do not increase frequency of defecation just soften stool
50
Q

Irritant laxatives

A
  • bisacodyl: orally or rectally
  • induce moderate inflammation leading to reduced water absorption and increased motility
  • safe but overdose causes catharsis
  • don’t chew tablets or mix with milk or antacids to ensure tablet reaches site of action in small intestine and avoid gastric irritation***
51
Q

Castor oil

A
  • smooth muscle stimulant: used as laxative, catharsis, induce labor
  • made from ricinus communis (castor bean): produces ricin (toxic) and oil ricinoleic acid (not toxic)
  • speeds motility in small bowel
  • 4 ml for laxative effect in four hours, 16ml for cathartic effect
52
Q

Bulk forming laxatives

A
  • fiber based: material not broken down, material stimulates peristalsis
  • examples: methylcellulose, psyllium, polycarbophil
  • great for regular soft stools
  • adverse: exacerbate intestinal obstructions, absorption of other drugs
53
Q

Mechanism of antidiarrheal agents

A
  • bulk forming agents: reduce fluidity without reducing water content
  • opioids: reduce motility to increase transit time and water absorption
  • octreotide: reduce secretions
54
Q

Antidiarrheal: bulk forming agents

A
  • based on colloids or polymers
  • absorb water within GI tract to decrease stool fluidity
  • only provides symptomatic relief
55
Q

Diphenoxylate & difenoxin

A
  • opioid
  • difenoxin is the active metabolite of diphenoxylate
  • piperidine derivatives
  • can have CNS effectspackaged with atropine to discourage abuse
56
Q

Loperamide

A
  • opioid
  • 40-50X more potent than morphine
  • does not enter CNS
57
Q

Paregoric

A
  • opioid
  • has 2mg morphine per 5 ml
  • adults 5-10 ml, 1-4 doses daily; children .25-.5mg/kg/dose
58
Q

Octreotide: uses, adverse

A
  • somatostatin derivative
  • use: combat secretory diarrhea of hormone secreting tumors, post surgical gastric dumping syndrome and diarrhea associated with chemo, rest the pancreas with pancreatitis
  • adverse: nausea, bloating, injection site pain; long term therapy may result in gallstones
59
Q

Bismuth subsalicylate (Pepto Bismol)

A
  • bismuth: 99% unabsorbed and eliminated in feces, anti secretory, anti inflammatory, anti microbial, commonly included in H. pylori treatments
  • salicylate: released in acidic stomach, NSAID activity absorbed systemically
  • Mg aluminum silicate (clay): bulk forming effects
60
Q

Irritable bowel syndrome: process and symptoms

A
  • NON-inflammatory bowel disorder

- characterized by chronic abdominal pain and bloating w/ alternating constipation/diarrhea

61
Q

Irritable bowel syndrome: treatment

A
  • alosetron: 5HT3 antagonist use for diarrhea predominant IBS; produces effects opposite of 5HT4 agonists, also reducing visceral sensitivity by reducing vagal nerve signaling; can produce serious constipation and potentially FATAL ischemic colitis
  • tegaserod: 5HT4 agonist used for constipation predominant IBS
62
Q

Emesis

A
  • controlled centrally by chemoreceptor trigger zone (CTZ) in fourth ventricle and can sense both spinal fluid and blood; solitary tract nucleus (STN) of the vagus nerve
  • peripheral input: senses, inner ear, small intestine, pharynx
63
Q

Antiemetics: serotonin receptor (5HT3) antagonists

A
  • serotonin promotes gut motility
  • act centrally at the CTZ and the STN
  • act peripherally in small intestine
  • use: chemo induced emesis and nausea
  • Ondansetron is prototype of the class
64
Q

5-HT3 antagonist

A
  • ondasetron: 3.9 hrs
  • granistron: 9-11.6 hrs
  • dolasetron: 7-9 hrs
  • palonosetron: 40 hrs; highest affinity for receptor in this class
65
Q

5-HT3 antagonists: adverse reactions

A
  • constipation, diarrhea, headache, light headedness
66
Q

Dopamine receptor antagonists

A
  • metoclopramide
  • some antagonism of 5-HT3
  • effects CTZ, also increase forward motility; stops emesis promotes defecation
  • preferred agent for chemo induced nausea
67
Q

Dopamine receptor antagonists: phenothiazines

A
  • prochlorperazine, chlorpromazine
  • preferred for general anti nauseants & anti emetics
  • targets D2 receptors in CTZ, and H1 receptors
  • good for motion sickness (H1 effects)
68
Q

Dopamine receptor antagonists: adverse reactions

A
  • parkinson like symptoms, extrapyramidal side effects

- may cause dissociative dysphoria in psychiatrically normal patients

69
Q

Antiemetic: antihistamines

A
  • H1 receptor antagonists
  • use: motion sickness, post op emesis
  • acts on brainstem and vestibular apparatus
70
Q

Antihistamine: drugs

A
  • cyclizine, promethazine, hydroxyzine: act on STN
  • diphenhydramine: act on cerebellum
  • cyclizine also has anticholinergic effects used in patients with abdominal cancer
71
Q

Anticholinergics: process

A
  • muscarinic ACh receptor antagonists
  • scopolamine can be sued parenterally, more commonly trans dermal
  • effective short or long term prevention of motion sickness
  • acts on vestibular apparatus
  • not effective for chemo induced nausea, minimal CTZ effects
72
Q

Anticholinergics: adverse effects

A
  • dry mouth, blurred vision

- outbursts of uncontrolled behavior when used in presence of pain or anxiety

73
Q

Syrup of ipecac

A
  • given orally shortly after ingesting toxin/drug
  • acts on CTZ
  • superseded by activated charcoal, b/c of danger of aspiration
74
Q

Apomorphine

A
  • D2 agonists, acts locally and on CTZ
  • given sub-Q
  • largely superseded by activated charcoal
  • used more in veterinary medicine
75
Q

Most potent stimulator for acid release

A

Gastrin

MODHIII - Unit 3 (20 decks)

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