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10. GI drugs Flashcards

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1
Q

ach and gastric pathways to produce acid

A

phospholipase c
ip3 and dag
ca release

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2
Q

histamine and proostaglandins pathways

A

g coupled
camp
protein kinase

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2
Q

antacids

A

Antacids are basic compounds that used to neutralize hyperacidity of the gastric contents.

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3
Q

antiacids Broadly classified in to:

A

1) Non-systemic or local, and
2) Systemic antacids.

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4
Q

local define plus example

A

Local/non-systemic antacids : which are non absorbable from GIT & preferable in the treatment of peptic ulcer than the absorbable(systemic) antacids. they include:
Magnesium hydroxide/magnesium trisilicate, aluminum hydroxide

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5
Q

local antiacids differ in

A

Differ in terms of acid neutralizing capacity, onset and duration of action, and adverse effects

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6
Q

Magnesium hydroxide

A

Magnesium hydroxide has very good acid neutralizing capacity, rapid onset and relatively short duration of action

causes diarrhea with prolonged use

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7
Q

Aluminum hydroxide

A

Aluminum hydroxide has relatively low acid neutralizing capacity, slow onset but prolonged duration of action

causes constipation with prolonged use due to aluminum’s smooth muscle relaxant and mucosal astringent action

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8
Q

Aluminum hydroxide binds ………. in the intestine and prevents its absorption

A

phosphate

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9
Q

Rebound acidity is mild and brief upon withdrawal of both

A
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10
Q

Calcium carbonate is a potent and rapidly acting(but not commonly used)
because

A

Liberates carbon dioxide can cause distention and discomfort
Calcium diffuses in to gastric mucosa increase HCl production directly by parietal cells(rebound acidity more marked)

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11
Q

Combinations of magnesium and aluminum salts are preferred b/c:

A

Adverse effects will cancel out( diarrhea and constipation)

Rapid action of magnesium salts combined with long action of aluminum salts maximizes the beneficial effects

Different combination preparations are available

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12
Q

sodium bicarbonate rarely used as gastric antacid b/c:

A

Produces carbon dioxide in stomach → cause distention, discomfort and ulcer perforation

Alters(increases) the pH of blood & other body fluids

Effect is short lasting and rebound acidity

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13
Q

H2 antagonists
define plus type

A

Counteract the hypersecretory effect of the endogenous histamine.
reversible competitive antagonists

Include: cimetidine(prototype), ranitidine, nizatidine, famotidine

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14
Q

All have equal efficacy but differ in terms of

A

potency

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15
Q

Cimetidine

A

inhibits cytochrome P450 and can slow metabolism and, thus, potentiate the action of several drugs ( warfarin, diazepam, phenytoin, quinidine, carbamazepine etc.)

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16
Q

side effects of cimetedine

A

It has antiandrogenic effect that manifest as gynecomastia, loss of libido, impotence, decreased sperm count

displacement of dihydrotestosterone from androgen receptors and increased prolactin release and inhibits degradation of estradiol by the liver

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17
Q

Uses of H2 antagonists

A

Duodenal ulcer
Gastric ulcer
Stress ulcers and gastritis
Zollinger-Ellison syndrome
GERD
However, b/c of higher efficacy of PPIs and equally good tolerability, they are not first-line agents

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18
Q

Proton Pump Inhibitors(PPIs)
dfine plus example

A

Are prodrugs activated in acidic environment of parietal cells’ canaliculi(charged form binds the enzyme)
Can be inactivated in the stomach and the presence of food decreases their bioavailability(given one hour before meal)
Example: Omeprazole(prototype), lansoprazole, pantoprazole, esomeprazole…

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19
Q

Mechanism of Action of ppi

A

Irreversibly bind to H+/K+ ATPase enzyme and inhibit it.

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20
Q

Steady state concentrations cause 80-98% inhibition of acid secretion.(Although their half-lives are 1-2 hours have long lasting effect; once daily administration

A
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21
Q

Duodenal ulcer heals faster than gastric ulcer(healing can be enhanced by 40 mg in both DU and GU)

A
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22
Q

ppi use

A

1) Peptic ulcer(omeprazole 20 mg is equally or more effective than H2 blockers)
Duodenal ulcer heals faster than gastric ulcer(healing can be enhanced by 40 mg in both DU and GU)
Are drugs of choice for NSAIDs-induced peptic ulcers
Can prevent relapse also

2) Bleeding peptic ulcer: acid enhances clot dissolution promoting ulcer bleed
Suppression of gastric acid facilitates clot formation reducing blood loss & rebleed
3) Stress ulcers
4) GERD
5) Zollinger-Ellison syndrome
6) Prophylaxis of aspiration pneumonia

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23
Q

Cytoprotective(ulcer protective) Agents
define plus drugs

A

Enhance mucosal protective mechanisms
Some may reduce acid secretion and exert antibacterial activity as well
Drugs include: sucralfate, colloidal bismuth subcitrate, tripotassium dicitratobismuthate, misoprostol

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24
Sucralfate used for
Used for stress ulcers, erosions, PUD
25
Sucralfate Attracted to and binds to
the base of ulcers and erosions, forming a protective barrier over these areas and protects the areas from acid and pepsin, action entirely local
26
sucralfate also augments gastric mucosal synthesis of
prostagladin
27
sucralfate is Preferred in patients who
continue to smoke
28
Antacids should not be taken with sucralfate as its action requires
acid pH
29
Misoprostol
Synthetic prostaglandin analogue
30
Prostaglandins have cytoprotective activity:
Protect gastric mucosa from injury by enhancing local production of mucus or bicarbonate Acid secretion and gastrin production are inhibited Helps to maintain mucosal blood flow
31
Major problems in the use of misoprostol are
abdominal cramps, diarrhea, uterine bleeding, abortion
32
Colloidal bismuth subcitrate:
water soluble but precipitates at pH < 5 It heal 80-90 % of ulcers at 8 weeks
33
Possible mechanisms of action: of colloid bismuth subcitrate
Stimulation of mucosal prostaglandin production Formation of a coat on the ulcer Detaches H. pylori from the surface of mucosa and kills it
34
Triple Therapy for H. pylori
One PPI plus 2 antibiotics each BID for 2 wks. Omeprazole(20mg) + Clarithromycin(500mg) + Amoxicillin (1g) Omeprazole(20mg) + Clarithromycin(500mg) + Metronidazole( 500mg) Particularly useful in penicillin allergy
35
Antidiarrheal drugs Principles of management:
Treatment of fluid depletion, shock and acidosis Maintenance of nutrition Drug therapy
35
anti diarrheal should not be used in patients with
bloody diarrhea, high fever, or systemic toxicity because of the risk of worsening the underlying condition.
36
Oral rehydration is possible if glucose is added with salt/glucose coupled sodium transport
37
Drug therapy consists of:
Specific antimicrobial drugs Nonspecific antidiarrheal drugs
38
Specific antimicrobials
co-trimoxazole, ciprofloxacin, norfloxacin, ampicillin, tetracycline, and erythromycin Diarrhea due to protozoa(amebiasis and giardiasis) can be treated with metronidazole and diloxanide furoate
39
Nonspecific antidiarrheal agents include:
1) Adsorbants 2) Antisecretory drugs 3) Antimotility drugs
40
Adsorbants include plus moa
activated charcoal, kaolin Coat the walls of the GI tract Bind to the causative bacteria or toxin, which are then eliminated through the stool
41
Antisecretory drugs include
include sulfasalazine, mesalazine, corticosteroids Reduce water secretion in to intestine Used for treatment of inflammatory bowel diseases
42
Antimotility drugs include
opioids such as loperamide, diphenoxylate and codeine Decrease propulsive movements and diminish intestinal secretions while enhancing absorption
43
Uses of Laxatives/ purgatives/ cathartics
Constipation(main use); other uses include: Expulsion of parasites after antihelimentic use Clear alimentary tract before surgery and radiological procedures For management of poisonings
44
Laxatives should be avoided if there is
an intestinal obstruction, severe abdominal pain, symptoms of appendicitis, ulcerative colitis,
45
Classes of Laxatives:
Bulk-forming laxatives Emollient/stool softeners Osmotic laxatives Stimulant/ irritant laxatives
46
Bulk-Forming MOA plus example
Highly fiber non-digestible and non-absorbable hydrophilic colloids Absorb water to increase bulk and swell Distends bowel to initiate reflex bowel activity Examples: psyllium, methylcellulose
47
Emollient / Stool softeners
Act by softening stool Lubricate the fecal material and intestinal walls Examples: Stool softeners: docusate salts Lubricants: liquid paraffin (10 ml every 8-12 hrs as required) Glycerin suppository (1 gm rectally at night after moistening with water)
48
Osmotic laxatives
Soluble but non-absorbable compounds whose osmotic action draws water in to the intestinal lumen. Result: bowel distention, increased peristalsis, and evacuation Examples: magnesium sulfate , Mg(OH)2, magnesium citrate, sodium phosphate, sorbitol, lactulose
49
Use of osmotic laxatives
Chronic constipation Bowel diagnostic and surgical preparations Removal of helminthes and parasites
50
Stimulant Laxatives
Stimulate intestinal enteric nerves system and leads to increase in intestinal motility and fluid secretion Examples: castor oil, senna, cascara, bisacodyl
51
Use
Acute constipation Diagnostic and surgical bowel preparations
52
Emetics
Example: ipecac syrup and apomorphine
53
Emesis should not be induced if the patient has ingested certain
volatile hydrocarbons and caustic substances, CNS stimulants
54
anti emetics include
Antihistamines Anticholinergics Dopamine Antagonists Phenothiazine Derivatives 5-HT3 receptor antagonists
55
Antihistamines
Example: Dimenhydrinate, diphenhydramine, and meclizine hydrochloride block peripheral stimulation of the emetic center. Most effective in motion sickness
56
S/E C/I:
S/E: sedation. C/I: active work such as driving
57
Anticholinergics
Example: Atropine, scopolamine (hyoscine) They block Muscarinic receptors in the GIT and inhibit motility and secretion.
58
Dopamine Antagonists
Example: Metoclopramide Dopamine antagonist that centrally inhibits stimulation of the CTZ decreasing a peripherally associated stimulation of the emetic center. S/E: drowsiness, fatigue, dizziness, weakness
59
Phenothiazine Derivatives
Example: Promethazine , Chlorpromazine, prochlorperazine Act at the CTZ by inhibiting dopaminergic transmission. They also decrease vomiting caused by gastric irritants, suggesting that they inhibit stimulation of peripheral vagal and sympathetic afferents.
60
5-HT3 receptor antagonists
ondansetron, granisetron
61
serotonin receptor antagonists use 3
chemotherapy induced vomiting, disease-induced vomiting, and post-operative vomiting

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