Pharmacology Flashcards
Examples of PPI
Omeprazole
esomeprazole
lansoprazole
Examples of antacids
Gaviscon
Calcium carbonate
Magnesium hydroxide
Mechanism of action of histamine receptor antagonists (H2 blockers)
Prevents histamine from binding to the H2 blockers on parietal cells -> adenylyl cyclase not activated -> cAMP not produced -> PKA not produced -> proton pump not activated
What activates PKG
cGMP
What is the effect of cGMP on smooth muscle
smooth muscle relaxation
Examples of H2 receptor antagonists
ranitidine
cimetidine
nizatidine
famotidine
NSAID mechanism of action
Inhibits COX1 , COX2 and prostaglandin E2
What type of NSAID is aspirin
Non-selective NSAID, but weakly more selective for COX1
Function of COX1 and COX2
Produce prostaglandin E2 to protect the GI lining
How does PGE2 protect the lining of GI mucosa
It stimulates the production of mucus and inhibits gastric acid and pepsin production
How does NSAID cause peptic ulcers
NSAID inhibits the production of prostaglandin E2, COX1 and COX2 hence decreases the production of protective mucous and inhibition of gastric acid secretion and pepsin. This leads to overproduction of acid and damage of the lining
Use of aminosalicylates
In ulcerative colitis
How is mesalazine metabolised in the liver
By adding acetyl group to mesalazine, forming mesalamine to be excreted in urine
Side effects of PPI
Headache Diarrhea Constipation Dizziness Nausea Increases pH reducing defense against bacteria
Contraindications for PPI
- for those that will be testing for H. pylori
- for those that have red flag symptoms and will be undergoing endoscopy
Why shouldn’t PPI be used in patients with red flag symptoms before their endoscopy
PPI might mask malignancy
Use of H2 receptor antagonists
second line treatment for GORD
Use of PPI
first line for GORD first line PUD H.pylori infection (antibiotics + PPI) Bleeding PUD Functional dyspepsia
Long term use of PPI can increase the patient’s susceptibility for which infections
C. difficile infection
pneumonia
How does PPI cause pneumonia
PPI increases pH which decreases the ability to kill pathogen hence the pathogen may then be aspirated and cause pneumonia
What are the drugs used for Crohn’s disease to induce remission
Glucocorticoids - prednisolone / IV hydrocortisone
azathioprine / methotextrate / mercaptopurine
When should azathioprine / methotrexate / mercaptopurine be used in inducing remission for Crohn’s disease
If glucocorticoids are not tolerated or are ineffective
What drugs are used to maintain remission in Crohn’s disease
azathioprine / mercaptopurine
methotrexate
When should methotrexate be used in Crohn’s
If azathioprine / mercaptopurine is not tolerated or is ineffective
What are the drugs used to induce remission in mild ulcerative colitis
topical or oral aminosalicylate (5-ASA)
Examples of aminosalicylates
Mesalazine
sulfasalazine
Olsalazine
What is the second line treatment for mild ulcerative colitis
aminosalicylate + oral prednisolone
What is the third line of treatment for mild ulcerative colitis
aminosalicylate + oral prednisolone + oral tacrolimus
What drug is used to treat acute severe ulcerative colitis
IV corticosteroids
What is the second line treatment for acute severe ulcerative colitis
IV corticosteroid + IV ciclosporin
or surgery
Why isn’t morphine used for biliary colic
Because morphine worsens biliary colic; it causes constriction of sphincter of Oddi
Which analgesia is used for biliary colic
NSAID
buprenophrine
AVOID MORPHINE
Biliary spasm is relieved by
atropine
GTN
Loperamide type of drug
Opioids (opiates)
u-opioid agonist
Examples of anti-diarrheal drugs
Loperamide
Diphenoxylate
Mechanism of action of opioids
acts on the μ-opioid receptors, decrease activity of myenteric plexus hence decreases tone of contraction of longitudinal and circular muscles = decreases peristalsis
Increases fluid reabsoprtion
Increases constriction of sphincters
Side effects for opiates
Sedation
Respiratory depression
Constipation
Types of laxatives
Bulk forming laxative
Osmotic laxative
Example of bulk forming laxative
Isphagula husk
Bulk forming laxative mechanism of action
Absorb water from the lumen of intestines, forming soft bulky stool. The presence of bulky mass stimulates peristaltic contraction
Osmotic laxative mechanism of action
Pulls water from surrounding tissue into the lumen by osmosis, softening the stool
When are laxatives used
Consatipation
IBS-C
Function of vomiting center
Coordinates vomiting signals from the CTZ, gut, peripheries and cortical centres
Where is the vomiting center located at
Brainstem
Where is the cortical center located at and what is its function
In the brain, senses pain / repulsive sights and smells / emotional factors
What are the main neurotransmitters involved in triggering nausea and vomiting
ACh, 5HT and dopamine
What receptors are present in chemoreceptor trigger zone
5HT3 receptors
Dopamine receptors
Where is CTZ located
In medulla oblongata
What receptor is present in the brain
Histamine 1 receptor
Route of emetic signals
Enterochromaffin cells in gut sense toxin -> vagal afferents to send signals from the gut -> CTZ -> vomiting center
Cortical center -> vomiting center
Types of anti-emetic drugs
H1 receptor antagonist Muscarinic ACh antagonist 5HT3 receptor antagonist Dopamine receptor antagonist Neurokinin-1 receptor antagonist
Examples of H1 receptor antagonists
Cyclizine
promethazine
diphenhydramine
Use of histamine 1 receptor antagonist
Nausea/vomiting due to motion sickness
Side effect of H1 receptor antagonist
Sedation
Side effect of H1 receptor antagonist
Sedation
Why may H1 antagonist cause sedation
Because H1 receptors in other parts of brain are involved in sleep response
Where are M1 receptors found
Cerebral cortex
Gastric, salivary glands
Parasympathetic ganglion
M1 receptor antagonist example
Scopolamine
Use of scopolamine
Nausea / vomiting due to motion sickness
Side effects of M1 receptor antagonist
Tachycardia
Dry mouth
Constipation
Why may scopolamine cause constipation
Because scopolamine is non-selective muscarinic receptor antagonist, can bind to M3 receptors on smooth muscles; peristalsis in colon can be enhanced by parasympathetic stimulation
Why can scopolamine cause tachycardia
Because it is a non-selective muscarinic receptor antagonist, it can act on M2 receptors in cardiac muscle. This reduces parasympathetic tone on HR hence causes tachycardia (there is always a parasympathetic tone on HR to decrease HR to normal range)
Example of 5HT3 receptor antagonist
Ondansetron
Granisetron
Palonosetron
Where are 5HT3 receptors found
In chemoreceptor trigger zone and in the GI tract (enteric nervous system)
Effect of 5HT3 on gi tract
Regulate motility, secretion of the gut
Pain sensation
Side effects of 5HT3 antagonist
Constipation
Diarrhea
Headache
How does 5HT3 antagonist cause constipation
Because 5HT3 are expressed on presynaptic efferents of parasympathetic innervation. When 5HT3 receptors are activated, ACh will be released from presynaptic neurone and ACh increases peristaltic contractions
So 5HT3 antagonist reduces peristaltic contractions = constipation
How does 5HT3 antagonist cause diarrhea
5HT3 in enteric nervous system regulates motility. Blocking 5HT3 = impaired motility = diarrhea
Examples of dopamine receptor antagonist
Chlorpromazine Droperidol Haloperidol Prochlorperazine Metoclopramide Domperidone
Where are dopamine 2 receptors (D2R) located
CTZ and gut
Side effects of Dopamine 2 receptor antagonists
Diarrhea extrapyramidal effects (feeling restless / muscles contract involuntarily)
Which dopamine 2 receptor antagonist does not have extra pyramidal effects
Domperidone
Which dopamine 2 receptor antagonist increases lower oesophageal sphincter tone
domperidone, causing food unable to enter the stomach
Uses of rifaximin
HE
traveller’s diarrhea caused by e.coli
IBS-D
Which laxative should be avoided in opioid-induced constipation
Bulk-forming laxative
Because bulk forming laxative try to stimulate peristalsis but opioid blocks peristalsis hence this will worsen abdominal pain and constipation
Which laxatives should be used for chronic constipation
Bulk-forming laxative first
If ineffective, add osmotic laxative
Example of osmotic laxative
Macrogols
Lactulose
Which dopamine receptors do metoclopramide act on
Metoclopramide is more selective towards D1 receptor in CTZ
Which dopamine receptors do domperidone act on
Domperidone is peripherally selective towards D2 and D3
What are the other effects of domperidone
Increases motility in upper GI tract and increases lower oesophageal sphincter tone
Effect of dopamine in GI tract
Inhibits motility in upper GI
Stimulates motility in colon
Contraindication of metoclopramide
Intestinal obstruction
Bleeding in GI tract
Perforation in GI tract
Sulfasalazine is metabolised by
Intestinal bacteria to release 5-ASA
When should 5HT3 antagonist be used
In nausea and vomiting due to chemotherapy
Effects of 5HT3 agonists on GI tract
Increase motility
Increase secretion