B5 The pharmacological basis of therapy Flashcards
Do antacids provide a cure?
no but they provide relief
Give examples of antacids
sodium bicarbonate
magnesium hydroxide
aluminium hydroxide
How to alginates work?
alginic acid combine with saliva and forms a viscous foam, this floats on the gastric contents forming a raft which protects the oesophagus during reflux
Why not use atropine?
suppresses acid production but has antimuscarinic side effects
What are examples of H2 receptor antagonists?
cimetidine
ranitidine
famotidine
Are H2 receptor antagonist drugs for long term or short term use and what class are the low and high doses?
short term
low-OTC
high-POM
What does maximum response equal?
efficacy of drug
What does EC50 equal?
concentration of agonist giving 50% of maximal response- potency
What are on the x & y axis of a competitive receptor antagonism graph?
x- log conc of agonist
y- pharmacological response
How to antagonists work?
they bind at the same site as the agonist & so reduce action of agonist by competition
How can completion from an antagonist be overcome?
increase conc of agonist
What is antagonist affinity a measure of?
how well the drug binds to a receptor
What is the affinity constant Ka measured in?
molar^-1
What is Kd or 1/Ka?
dissociation constant, is the conc at which the drug occupies half the receptor population
Will a high affinity drug have a high or low Kd?
low
What does pA2=?
-logKd
What does high PA2 mean for affinity?
high affinity
What are the benefits of H2RAs?
reduce gastric acid secretion
provide symptomatic relief
What are H1 receptor antagonists?
antihistamines
Why is cimetidine not chosen over ranitidine?
cimetidine inhibits cytochrome P450 & therefore the metabolism of other drugs, whereas ranitidine does not interact this way
What drugs does cimetidine interact with?
oral anticoagulants
phenytoin
carbamazepine
tricyclic antidepressants
What are examples of PPIs?
omeprazole, pantoprazole, lansoprazole
How to PPIs work?
activated by acidic pH, enter body, passes to parietal cells, pKa means activated at lower pH, localised action
What are possible ADRs of PPIs?
inhibit H+ secretion by > 90%, leads to achlorhydria (absence of HCl)
increase risk of campylobacter infection (food poisoning)
What is rebound acid hyper secretion?
following the cessation of H2RAs or PPIs, increase in acid release, increase in dyspepsia symptoms
How can you mange rebound acid hyper secretion?
with antacids
Give an example of a prostaglandin analogue?
misoprostol
How do prostaglandin analogues work?
agonist at PG receptor, suppress acid release and promote cytoprotection
What can prostaglandin analogues cause?
uterine contraction, cause miscarriage, abortion
How to pro kinetic drugs work?
cause gastric emptying, movement of gastric contents from stomach to duodenum
What are two examples of pro kinetic drugs and how do they work?
domperidone- increased closure of oesophageal sphincter and one lower sphincter
metoclopramide- act locally to increase gastric motility and emptying
What is the most effective treatment for long term cure of ulcers?
H.pylori eradication
What is TRIPLE THERAPY and how does it work?
involves an antibiotic, 2 from either; clarithromycin, amoxicillin, metronidazole plus PPI and/ or H2 antagonist
triple therapy lasts for one week then PPI alone
