Antagonists Flashcards
What are the 5 categories of antagonist action?
chemical, pharmacokinetic, physiological, non-competitive, competitive
Describe chemical antagonism
substances combine in solution so the effects of the active drug is lost
How does chemical antagonism cause loss of agonist
agonist is chemically altered
Give an example of chemical antagonist use
inactivation of heavy metal poison
How is the toxicity of heavy metals reduced
addition of a chelating agent
example of chelating agent
dimercaprol
Example of heavy metal poisons
mercury, lead and cadmium
What is the effect of pharmacokinetic antagonists
reduce the amount of drug absorbed, metabolised or excreted
How do pharmacokinetic antagonists decrease drug absorbtion
decrease absorption in the GI tract
What is an example of a drug reducing absorption
opiates reduce absorption by oral route
How do pharmacokinetic antagonists decrease absorption in the gut
inhibit gut motility
What does warfarin do
thins blood to prevent risk of strokes and heart attacks
How do pharmacokinetic antagonists change the excretion of an agonist
alter protein binding and filtration, alter urine pH and flow
Example of pharmacokinetic antagonist that changes the excretion of an agonist
diuretics
Describe physiological antagonism
interaction of two drugs with opposing actions in the body
Example of two interacting physiological antagonists
noradrenaline, histamine
What does histamine cause
vasodilation, lowers arterial pressure
What does noradrenaline cause
rise in arterial pressure - acts on blood vessels and heart
What does non competitive antagonist prevent
action of an agonist
What does non competitive antagonism block
step in process between receptor activation and response
TRUE or FALSE - non competitive antagonists compete with the agonist for the receptor site
false
What is a typical target for anti-hypertensive drugs
L type calcium channels
Example of a drug that targets L type calcium channels
Nifedipine
What is the effect of blocking L type calcium channels
reduces calcium signals, reduces muscle contraction
What works at the same site as the agonist
competitive antagonists
How can competitive antagonist effects be overcome
raising concentration of agonist
Describe the effect of increasing antagonist concentration on competitive antagonist concentration response curve
shifts the curve to the right, is parallel
What is the dose ratio
how many more times agonist is needed in the presence of an antagonist
What does the dose ratio give a measure of
shift of the dose response curve for given concentration of antagonist
What does the Schild analysis look at
relationship between dose ratio and concentration of antagonist added
What can Schild analysis be used to calculate
competitive antagonists affinity
Describe the relationship between pA2 value and affinity
higher the pA2 value the higher the affinity
Describe irreversible competitive antagonism
antagonism that cannot be reverse by washing the tissue
True or False - irreversible antagonism is time dependent
true
Example of an irreversible competitive antagonist
dibenamine
What is dibenamine
alkylating drug
What is desensitisation
effect of drug declines over time when given continuously or repeatedly
What are the physiological changes that can lead to desensitisation
loss of receptors from cell surface, change in receptor, exhaustion of mediators
What happens if you give frequent doses of salbutamol
B2 adrenoreceptors become phosphorylated - signalling shuts down
How are receptors lost from cell surface
receptors can be internalised
What can physiological adaptation occur in response to
thiazide diuretics
What receptors can be internalised
AMPA receptors, opiate receptors
