Receptor theory 4 Flashcards
What are the five types of antagonist?
- Chemical antagonist
- Pharmacokinetic antagonism
- Physiological antagonism
- Non-competitive antagonism
- Competitive antagonism by receptor block
What is an antagonists affinity for a receptor commonly used for
Used to identify and classify receptors
What is a chemical antagonist
A substance that combines in solution so that the effects of the active drug are lost
How does a chemical agent inactivate heavy metals?
Addition of a chelating agent
What is a pharmacokinetic antagonist
A substance that reduces the amount of drug absorbed e.g. drugs that inhibit opiates will reduce absorption by the oral route
How do pharmacokinetic drugs work
Creates changes in drug metabolism - patients taking warfarin have to be careful when taking antibiotics as they can stimulate the metabolism of warfarin so reducing its effective concentration in the blood stream
What is a physiological antagonist
The interaction of two drugs with opposing actions in the body
Give an example of physiological antagonism
Noradrenaline raises arterial BP by acting on the heart and peripheral blood vessels whereas histamine acts to lower arterial BP by causing vasodilation
What is non-competitive antagonism
Substance that blocks some step in the process between receptor activation and response
Give an example of non competitive antagonisim
Dihyldropyridines bind to and block certain calcium channels rather than the receptor that noradrenaline binds to
What is competitive antagonism
A substance that competes with the agonist for the occupancy of the receptor
What effect does atropine have on Ach binding in guinea pig ileum
Increased concentrations in antagonist cause a parallel shift to the right in the concentration response curve - the max response of Ach can still be reached but at a higher concentration
What is the dose ratio
How many more times the agonist is needed in the presence of the antagonist to cause the same percentage response - conc of agonist in the presence of the antagonist/ conc of agonist without the antagonist present
What is schild analysis used for
Derive the affinity of an antagonist for its receptor
How is pA2 related to Kd
pA2 is where the x intercept x-1 - and is -1(logKd)
