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Pharmacology > 14 Gastrointestinal tract drugs > Flashcards

14 Gastrointestinal tract drugs Flashcards

1
Q

14.01 H2 ANTAGONIST

Ranitidine, famotidine, cimetidine, nizatidine - actions

A

inhibit gastric acid secretion
inhibit the action of histamine released from mast cell-like cells in the gastric mucosa
partially inhibit acid secretion stimulated by gastrin or vagal stimulation

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2
Q

14.01 H2 ANTAGONIST

Ranitidine, famotidine, cimetidine, nizatidine - MOA

A

selective, reversible, competitive antagonism of histamine H2 receptors on parietal cells

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3
Q

14.01 H2 ANTAGONIST

Ranitidine, famotidine, cimetidine, nizatidine - abs/distrib/elim

A

given orally, rapidly absorbed
mainly renal excretion

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4
Q

14.01 H2 ANTAGONIST

Ranitidine, famotidine, cimetidine, nizatidine - clinical use

A

gastric and duodenal ulcers
gastro-oesophageal reflux disease
NSAID-induced ulcers (with discontinuation of NSAID)

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5
Q

14.01 H2 ANTAGONIST

Ranitidine, famotidine, cimetidine, nizatidine - adverse effects

A

uncommon
headache, GIT disturbances
anti-androgenic effects with cimetidine but not other H2 blockers: gynaecomastia in men, galactorrhoea in women

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6
Q

14.02 PROTON PUMP INHIBITORS

Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole - actions

A

inhibit gastric acid secretion

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7
Q

14.02 PROTON PUMP INHIBITORS

Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole - MOA

A

bind irreversibly to the H+/K+-ATPase (proton pump) in the gastric parietal cells to inhibit H+ transport
omeprazole (like other PPIs) is a prodrug - the acidic conditions in the parietal cell canaliculi convert the drug to the active form

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8
Q

14.02 PROTON PUMP INHIBITORS

Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole - abs/distrib/elim

A

given orally or IV but needs to be enteric coated to avoid deactivation by gastric acid before absorption
mainly eliminated by liver metabolism

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9
Q

14.02 PROTON PUMP INHIBITORS

Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole - clinical use

A

peptic and duodenal ulcers
gastro-oesophageal reflux disease
Zollinger-Ellison syndrome
as part of the triple therapy for Helicobacter pylori-dependent ulcers
treatment of NSAID-associated ulcers
PPIs are more effective than H2 antagonists

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10
Q

14.02 PROTON PUMP INHIBITORS

Omeprazole, lansoprazole, pantoprazole, rabeprazole, esomeprazole - adverse effects

A

generally safe
occasionally: headache, abdominal pain, diarrhoea, GI infections
rarely: hypomagnesaemia, fractures

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11
Q

14.03 MUCOSAL PROTECTANTS

Sucralfate, bismuth subsalicylate, tripotassium dicitratobismuthate - actions

A

local protective or healing action at GI mucosa
antibacterial effects

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12
Q

14.03 MUCOSAL PROTECTANTS

Sucralfate, bismuth subsalicylate, tripotassium dicitratobismuthate - MOA

A

these agents coat the ulcer/mucosa to protect against the action of acid and pepsin and may increase mucus and bicarbonate secretion
bismuth has antibacterial action against Helicobacter pylori

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13
Q

14.03 MUCOSAL PROTECTANTS

Sucralfate, bismuth subsalicylate, tripotassium dicitratobismuthate - abs/distrib/elim

A

very little of oral dose is absorbed into the systemic circulation

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14
Q

14.03 MUCOSAL PROTECTANTS

Sucralfate, bismuth subsalicylate, tripotassium dicitratobismuthate - clinical use

A

(I) indigestion and gastric or duodenal ulcers, bismuth is additionally used for eradication of H. pylori
(II) binds enterotoxins in treatment of diarrhoea (including travellers)

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15
Q

14.03 MUCOSAL PROTECTANTS

Sucralfate, bismuth subsalicylate, tripotassium dicitratobismuthate - adverse effects

A

sucralfate: constipation, formation of solid complexes (bezoars) in stomach
bismuth: nausea, vomiting, black stools

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16
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - actions

A

neutralise acid to raise pH in gut lumen

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17
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - MOA

A

antacids are weak bases that neutralise the HCl secreted in the stomach
the elevated pH also usefully reduces the activity of pepsin
stimulate prostaglandin synthesis

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18
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - abs/distrib/elim

A

aluminium and magnesium hydroxides are poorly absorbed from the gut (no systemic actions)
NaHCO3 and CaCO3 are absorbed and may have significant systemic actions

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19
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - clinical use

A

short-term symptom relief for duodenal ulcers
gastro-oesophageal reflux disease
need to be taken 5-7 times daily

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20
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - adverse effects

A

Al(OH)3 causes constipation
Mg(OH)2 has a strong laxative action (osmotic purgative)
NaHCO3 and CaCO3 release CO2, which causes belching and also metabolic alkalosis
CaCO3 causes hypercalcaemia

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21
Q

14.04 ANTACIDS

Aluminium or magnesium hydroxide, sodium bicarbonate, calcium carbonate - special points

A

calcium and aluminium salts complex with orally administered tetracyclines to prevent their absorption

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22
Q

14.05 PROSTAGLANDIN E AGONIST

Misoprostol - actions

A

promotes gastric ulcer healing
combats the ulcerogenic action of NSAIDs

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23
Q

14.05 PROSTAGLANDIN E AGONIST

Misoprostol - MOA

A

activates prostaglandin receptors (EP3 subtype) to inhibit acid secretion
effects via Gi-mediated inhibition of adenylate cyclase
also stimulates mucus and bicarbonate secretion

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24
Q

14.05 PROSTAGLANDIN E AGONIST

Misoprostol - abs/distrib/elim

A

given orally, well absorbed
rapidly hydrolysed to free acid (active moiety)
half-life 30-40 min

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25
Q

14.05 PROSTAGLANDIN E AGONIST

Misoprostol - clinical use

A

gastric ulcers, particularly those caused by NSAIDs and where the NSAIDs cannot be withdrawn
also used for induction of labour

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26
Q

14.05 PROSTAGLANDIN E AGONIST

Misoprostol - adverse effects

A

diarrhoea, abdominal cramps
should be avoided in pregnancy because of contractile action on uterus

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27
Q

14.06 5-HT3 ANTAGONISTS - ANTIEMETICS

Ondansetron, granisetron, dolasetron, tropisetron - actions

A

antiemetic

28
Q

14.06 5HT3 ANTAGONISTS - ANTIEMETICS

Ondansetron, granisetron, dolasetron, tropisetron - MOA

A

reversible competitive antagonism at 5-HT3 receptors in the chemoreceptor trigger zone and at the sensory endings of vagal afferents in the GIT

29
Q

14.06 5HT3 ANTAGONISTS - ANTIEMETICS

Ondansetron, granisetron, dolasetron, tropisetron - abs/distrib/elim

A

given orally or IV (if vomiting)
half-life 4-6h
metabolised by cytochrome P450 system in liver

30
Q

14.06 5HT3 ANTAGONISTS - ANTIEMETICS

Ondansetron, granisetron, dolasetron, tropisetron - clinical use

A

main agents for nausea and vomiting due to cytotoxic, anticancer drugs
often given prophylactically before starting chemotherapy
nausea and vomiting arising postoperatively or after radiation treatment
limited effectiveness in motion sickness

31
Q

14.06 5HT3 ANTAGONISTS - ANTIEMETICS

Ondansetron, granisetron, dolasetron, tropisetron - adverse effects

A

well tolerated
headache, GIT upsets

32
Q

14.07 OTHER ANTIEMETICS

Anticholinergics

A

hyoscine acts on the vestibular nuclei and vomiting centre
used for motion sickness

33
Q

15.07 OTHER ANTIEMETICS

Antihistamines

A

e.g. promethazine, cyclizine and cinnarizine
antiemetic action is due to blocking H1 receptors in the vestibular nuclei and vomiting centre

34
Q

14.07 OTHER ANTIEMETICS

Dexamethasone

A

mechanism of antiemetic action is not established
generally used in combination with other antiemetics during surgery or chemotherapy

35
Q

14.07 OTHER ANTIEMETICS

Cannabinoids

A

action via CB1 receptors
used for nausea and vomiting associated with cancer chemotherapy
dronabinol is the main active ingredient (tetrahydrocannabinol) of cannabis, nabilone is a synthetic analogue

36
Q

14.07 OTHER ANTIEMETICS

Neurokinin 1 (NK1) receptor antagonists

A

aprepitant blocks substance P receptors in the vomiting centre
adjunct for treatment of chemotherapy-induced and postoperative nausea and vomiting
orally active

37
Q

14.08 OSMOTIC LAXATIVES

Lactulose, macrogols, magnesium sulfate - actions

A

increase osmotic load
include magnesium salts, disaccharides (lactulose) and ethylene glycol polymers (macrogols)

38
Q

14.08 OSMOTIC LAXATIVES

Lactulose, macrogols, magnesium sulfate - MOA

A

poorly absorbed, these agents raise the osmotic load within the gut lumen
this causes ingested water to be retained and water to be withdrawn from the bloodstream
the increased fluid volume promotes movement along the gut

39
Q

14.08 OSMOTIC LAXATIVES

Lactulose, macrogols, magnesium sulfate - abs/distrib/elim

A

given orally
not absorbed

40
Q

14.08 OSMOTIC LAXATIVES

Lactulose, macrogols, magnesium sulfate - clinical use

A

constipation (lactulose and macrogols)
bowel cleansing prior to surgery or examination (MgSO4)
the effects of lactulose develop after 2-3 days

41
Q

14.08 OSMOTIC LAXATIVES

Lactulose, macrogols, magnesium sulfate - adverse effects

A

abdominal cramps, flatulence
few systemic actions because of low absorption

42
Q

14.09 BULK LAXATIVES

Methylcellulose, ispaghula husk, sterculia, bran - actions

A

purgative

43
Q

14.09 BULK LAXATIVES

Methylcellulose, ispaghula husk, sterculia, bran - MOA

A

these agents (polysaccharide polymers) are poorly absorbed and, being hygroscopic, form a soft faecal mass which distends the gut to promote peristalsis

44
Q

14.09 BULK LAXATIVES

Methylcellulose, ispaghula husk, sterculia, bran - abs/distrib/elim

A

given orally
not absorbed

45
Q

14.09 BULK LAXATIVES

Methylcellulose, ispaghula husk, sterculia, bran - clinical use

A

constipation
used if increasing dietary fibre has not helped
beneficial in various bowel disorders (e.g. haemorrhoids, irritable bowel syndrome)
maintain fluid intake to prevent intestinal obstruction

46
Q

14.09 BULK LAXATIVES

Methylcellulose, ispaghula husk, sterculia, bran - adverse effects

A

flatulence
few systemic actions because of low absorption
obstruction

47
Q

14.10 STIMULANT LAXATIVES

Bisacodyl, senna, glycerol - actions

A

laxative

48
Q

14.10 STIMULANT LAXATIVES

Bisacodyl, senna, glycerol - MOA

A

active metabolite of bisacodyl stimulates peristalsis by irritation of mucosa and/or an effect on the enteric nervous system
also increases fluid volume by promoting net fluid secretion into the lumen

49
Q

14.10 STIMULANT LAXATIVES

Bisacodyl, senna, glycerol - abs/distrib/elim

A

given orally or rectal
half-life 16h
senna is activated in the colon by bacteria

50
Q

14.10 STIMULANT LAXATIVES

Bisacodyl, senna, glycerol - clinical use

A

chronic constipation
bowel cleansing prior to surgery/investigation
action of bisacodyl is more rapid rectally (30 min) than orally (6h)

51
Q

14.10 STIMULANT LAXATIVES

Bisacodyl, senna, glycerol - adverse effects

A

abdominal cramps
tolerance to action with atony of the colon if used excessively

52
Q

14.11 FAECAL SOFTENERS

Docusate, liquid paraffin, arachis oil - actions

A

soften/lubricate the stool to allow easier passage along the gut and defaecation

53
Q

14.11 FAECAL SOFTENERS

Docusate, liquid paraffin, arachis oil - MOA

A

surfactant with emulsifying action
docusate has weak stimulant action

54
Q

14.11 FAECAL SOFTENERS

Docusate, liquid paraffin, arachis oil - abs/distrib/elim

A

docusate is given orally or rectally, arachis oil rectally

55
Q

14.11 FAECAL SOFTENERS

Docusate, liquid paraffin, arachis oil - clinical use

A

constipation
haemorrhoids

56
Q

14.11 FAECAL SOFTENERS

Docusate, liquid paraffin, arachis oil - adverse effects

A

well tolerated, possible abdominal cramping
liquid paraffin may impair the absorption of fat-soluble vitamins, and is seldom used nowadays

57
Q

14.12 OTHER DRUGS FOR CONSTIPATION

Prucalopride

A

selective 5-HT4 receptor agonist
marked prokinetic properties
used in chronic constipation when other types of laxatives have failed

58
Q

14.12 OTHER DRUGS FOR CONSTIPATION

Lubiprostone

A

activates the CIC-2 chloride channel in the apical membrane of the gastrointestinal epithelium
promotes chloride and fluid secretion into the lumen, which softens the stool and improves gut motility

59
Q

14.12 OTHER DRUGS FOR CONSTIPATION

Linaclotide

A

acts on guanylate cyclase-C receptor at the gut epithelium
greater secretion of intestinal fluid, chloride and bicarbonate ions, and more rapid intestinal transit

60
Q

14.12 OTHER DRUGS FOR CONSTIPATION

Naloxegol

A

similar to naloxone but does not penetrate the CNS
acts as a µ-opioid receptor antagonist to counteract opioid-induced constipation

61
Q

14.13 ANTIDIARRHOEAL AGENTS

Loperamide (similar: diphenoxylate, codeine) - actions

A

reduces gut motility and secretions
the slower transit time allows for more fluid absorption and more solid stools

62
Q

14.13 ANTIDIARRHOEAL AGENTS

Loperamide (similar: diphenoxylate, codeine) - MOA

A

agonist action at µ-opioid receptors in the myenteric plexus of the gut inhibits peristalsis
effects can be reversed by naloxone
loperamide and diphenoxylate (not codeine) achieve low concentrations in the CNS, so have few central effects (including analgesia and addiction)

63
Q

14.13 ANTIDIARRHOEAL AGENTS

Loperamide (similar: diphenoxylate, codeine) - abs/distrib/elim

A

given orally
metabolised by hepatic cytochrome P450 system
diphenoxylate is hydrolysed to an active metabolite

64
Q

14.13 ANTIDIARRHOEAL AGENTS

Loperamide (similar: diphenoxylate, codeine) - clinical use

A

acute diarrhoea
chronic diarrhoea associated with inflammatory bowel disease
diphenoxylate is commonly administered in a combined preparation with atropine

65
Q

14.13 ANTIDIARRHOEAL AGENTS

Loperamide (similar: diphenoxylate, codeine) - adverse effects

A

drowsiness, nausea
constipation, abdominal cramps
CNS depression may occur in overdose

66
Q

14.14 OTHER DRUGS THAT REDUCE GI MOTILITY

Eluxadoline

A

mixed opioid receptor agonist-antagonist acting on enteric neurons
improves stool consistency and slows the transit time
used in irritable bowel syndrome with predominant diarrhoea symptoms

67
Q

14.14 OTHER DRUGS THAT REDUCE GI MOTILITY

Racecadotril

A

prodrug of thiorphan
inhibits enkephalinase, which reduces the breakdown of enkephalins and alleviates excessive intestinal secretion
used in conjunction with rehydration therapy for acute diarrhoea

Pharmacology (34 decks)

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