Pharmacological basis of therapy Flashcards
Antagonist affinity
Measure of how well a drug binds to a receptor
Prostaglandin analogue
Misoprostol - agonist at PG receptors
Suppress acid release + promote cytoprotection
Cause uterine contractions
Prokinetic drugs
Cause gastric emptying - movement of gastric contents from stomach to duodenum (help GORD)
Example of prokinetic drugs
DOMPERIDONE
METOCLOPRAMIDE
What can metoclopramide be combined with?
Analgesics - to accelerate absorption
How do we eradicate H.pylori?
Triple therapy
What is triple therapy?
Combination therapy
What does triple therapy consist of?
2 antibiotics + PPI and/or H2RA
How long to take triple therapy?
1 week then PPI alone
Example of PPI
Omeprazole
Pantoprazole
Lansoprazole
What PPIs are OTC
Omeprazole + pantoprazole
Adverse effects of PPIs
Inhibit H+ secretion by more than 90% - leading to achlorydria
Increase risk of Campylobacter infection (food poisoning)
Adverse effects of PPIs
Inhibit H+ secretion by more than 90% - leading to achlorydria
Increase risk of Campylobacter infection (food poisoning)
What activates PPIs
Acidic pH
- enters body
- passes to parietal cells
- pka means activated at low pH
- localises action
What is rebound acid hypersecretion
Follows after cessation of H2RAs + PPIs
Increases acid release
Increase dyspepsia symptoms
Avoid prolonged usage
How do you treat/manage rebound acid hypersecretion?
Antacids
Affinity constant
Ka
Dissociation constant
1/Ka = Kd
Kd
Concentration at which the drug occupies half of the receptor population
A high affinity drug has…
A low Kd (low molarity drug)
Examples of H2RA
Cimetidine
Ranitidine
Nizatidine
Famotidine
H2RA
Coupled with adenylyl cyclase to increase cAMP
which activates the proton pump
Alginates
Combine with saliva to form viscous foam
Floats on gastric content forming a raft which protect oesophagus from reflux
Examples of antacids
Sodium bicarbonate
Magnesium hydroxide
Aluminium hydroxide
Domperidone
Increased closure of oesophageal sphincter (good for reflux) + opens lower sphincter
Metoclopramide
Acts locally to increase gastric motility + emptying
What are the antibiotic that can be used for triple therapy
Amoxicillin
Clarithromycin
Metronidazole
Calculate pA2
-logKd
Use of H2RAs
Reduce gastric acid secretion
- provide symptomatic relief
- promote ulcer healing
- reduce need of surgeru in ulceration
When are H2RAs best given
At night
Why does H2RAs have a lot of drug interactions
Inhibit cytochrome P450 + metabolism of drugs = drug interactions
What drugs metabolism are affected by H2RAs
Oral anticoagulants
Phenytoin
Carbamazepine
Tricyclic anti-depressants
What H2RA does not interact with other drugs
Ranitidine
Misoprostol
Agonist at PG receptor
Suppress acid secretion + promote cytoprotection
What do misoprostol cause
Uterine contractions
What are uterine contractions contra-indicated with
Females of child-bearing age
How do we accelerate absorption of metoclopramide
Combining it with analgesics
