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14 Gastrointestinal tract drugs Flashcards

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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
14.05 PROSTAGLANDIN E AGONIST Misoprostol - clinical use
gastric ulcers, particularly those caused by NSAIDs and where the NSAIDs cannot be withdrawn also used for induction of labour
26
14.05 PROSTAGLANDIN E AGONIST Misoprostol - adverse effects
diarrhoea, abdominal cramps should be avoided in pregnancy because of contractile action on uterus
27
14.06 5-HT3 ANTAGONISTS - ANTIEMETICS Ondansetron, granisetron, dolasetron, tropisetron - actions
antiemetic
28
14.06 5HT3 ANTAGONISTS - ANTIEMETICS Ondansetron, granisetron, dolasetron, tropisetron - MOA
reversible competitive antagonism at 5-HT3 receptors in the chemoreceptor trigger zone and at the sensory endings of vagal afferents in the GIT
29
14.06 5HT3 ANTAGONISTS - ANTIEMETICS Ondansetron, granisetron, dolasetron, tropisetron - abs/distrib/elim
given orally or IV (if vomiting) half-life 4-6h metabolised by cytochrome P450 system in the liver
30
14.06 5HT3 ANTAGONISTS - ANTIEMETICS Ondansetron, granisetron, dolasetron, tropisetron - clinical use
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
14.06 5HT3 ANTAGONISTS - ANTIEMETICS Ondansetron, granisetron, dolasetron, tropisetron - adverse effects
well tolerated headache, GIT upsets
32
14.07 OTHER ANTIEMETICS Anticholinergics
hyoscine acts on the vestibular nuclei and vomiting centre used for motion sickness
33
15.07 OTHER ANTIEMETICS Antihistamines
e.g. promethazine, cyclizine and cinnarizine antiemetic action is due to blocking H1 receptors in the vestibular nuclei and vomiting centre
34
14.07 OTHER ANTIEMETICS Dexamethasone
mechanism of antiemetic action is not established generally used in combination with other antiemetics during surgery or chemotherapy
35
14.07 OTHER ANTIEMETICS Cannabinoids
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
14.07 OTHER ANTIEMETICS Neurokinin 1 (NK1) receptor antagonists
aprepitant blocks substance P receptors in the vomiting centre adjunct for treatment of chemotherapy-induced and postoperative nausea and vomiting orally active
37
14.08 OSMOTIC LAXATIVES Lactulose, macrogols, magnesium sulfate - actions
increase osmotic load include magnesium salts, disaccharides (lactulose) and ethylene glycol polymers (macrogols)
38
14.08 OSMOTIC LAXATIVES Lactulose, macrogols, magnesium sulfate - MOA
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
14.08 OSMOTIC LAXATIVES Lactulose, macrogols, magnesium sulfate - abs/distrib/elim
given orally not absorbed
40
14.08 OSMOTIC LAXATIVES Lactulose, macrogols, magnesium sulfate - clinical use
constipation (lactulose and macrogols) bowel cleansing prior to surgery or examination (MgSO4) the effects of lactulose develop after 2-3 days
41
14.08 OSMOTIC LAXATIVES Lactulose, macrogols, magnesium sulfate - adverse effects
abdominal cramps, flatulence few systemic actions because of low absorption
42
14.09 BULK LAXATIVES Methylcellulose, ispaghula husk, sterculia, bran - actions
purgative
43
14.09 BULK LAXATIVES Methylcellulose, ispaghula husk, sterculia, bran - MOA
these agents (polysaccharide polymers) are poorly absorbed and, being hygroscopic, form a soft faecal mass which distends the gut to promote peristalsis
44
14.09 BULK LAXATIVES Methylcellulose, ispaghula husk, sterculia, bran - abs/distrib/elim
given orally not absorbed
45
14.09 BULK LAXATIVES Methylcellulose, ispaghula husk, sterculia, bran - clinical use
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
14.09 BULK LAXATIVES Methylcellulose, ispaghula husk, sterculia, bran - adverse effects
flatulence, few systemic actions because of low absorption, obstruction
47
14.10 STIMULANT LAXATIVES Bisacodyl, senna, glycerol - actions
laxative
48
14.10 STIMULANT LAXATIVES Bisacodyl, senna, glycerol - MOA
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
14.10 STIMULANT LAXATIVES Bisacodyl, senna, glycerol - abs/distrib/elim
given orally or rectally half-life 16h senna is activated in the colon by bacteria
50
14.10 STIMULANT LAXATIVES Bisacodyl, senna, glycerol - clinical use
chronic constipation bowel cleansing prior to surgery/investigation action of bisacodyl is more rapid rectally (30 min) than orally (6h)
51
14.10 STIMULANT LAXATIVES Bisacodyl, senna, glycerol - adverse effects
abdominal cramps tolerance to action with atony of the colon if used excessively
52
14.11 FAECAL SOFTENERS Docusate, liquid paraffin, arachis oil - actions
soften/lubricate the stool to allow easier passage along the gut and defaecation
53
14.11 FAECAL SOFTENERS Docusate, liquid paraffin, arachis oil - MOA
surfactant with emulsifying action docusate has weak stimulant action
54
14.11 FAECAL SOFTENERS Docusate, liquid paraffin, arachis oil - abs/distrib/elim
docusate is given orally or rectally, arachis oil rectally
55
14.11 FAECAL SOFTENERS Docusate, liquid paraffin, arachis oil - clinical use
constipation haemorrhoids
56
14.11 FAECAL SOFTENERS Docusate, liquid paraffin, arachis oil - adverse effects
well tolerated, possible abdominal cramping liquid paraffin may impair the absorption of fat-soluble vitamins, and is seldom used nowadays
57
14.12 OTHER DRUGS FOR CONSTIPATION Prucalopride
selective 5-HT4 receptor agonist marked prokinetic properties used in chronic constipation when other types of laxatives have failed
58
14.12 OTHER DRUGS FOR CONSTIPATION Lubiprostone
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
14.12 OTHER DRUGS FOR CONSTIPATION Linaclotide
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
14.12 OTHER DRUGS FOR CONSTIPATION Naloxegol
similar to naloxone but does not penetrate the CNS acts as a µ-opioid receptor antagonist to counteract opioid-induced constipation
61
14.13 ANTIDIARRHOEAL AGENTS Loperamide (similar: diphenoxylate, codeine) - actions
reduces gut motility and secretions the slower transit time allows for more fluid absorption and more solid stools
62
14.13 ANTIDIARRHOEAL AGENTS Loperamide (similar: diphenoxylate, codeine) - MOA
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
14.13 ANTIDIARRHOEAL AGENTS Loperamide (similar: diphenoxylate, codeine) - abs/distrib/elim
given orally metabolised by hepatic cytochrome P450 system diphenoxylate is hydrolysed to an active metabolite
64
14.13 ANTIDIARRHOEAL AGENTS Loperamide (similar: diphenoxylate, codeine) - clinical use
acute diarrhoea chronic diarrhoea associated with inflammatory bowel disease diphenoxylate is commonly administered in a combined preparation with atropine
65
14.13 ANTIDIARRHOEAL AGENTS Loperamide (similar: diphenoxylate, codeine) - adverse effects
drowsiness, nausea constipation, abdominal cramps CNS depression may occur in overdose
66
14.14 OTHER DRUGS THAT REDUCE GI MOTILITY Eluxadoline
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
14.14 OTHER DRUGS THAT REDUCE GI MOTILITY Racecadotril
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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