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How do drugs work?
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A summary of the lecture on competitive and non competitive antagonist, partial agonists and drug tolerance and tachyphylaxis.
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PHARMACOLOGYHow do drugs work?
Agonists vs Antagonists
An agonist binds reversibly to a receptor to evoke a response, it has high affinity and
efficacy.
An antagonist binds reversibly to the same receptor, blocking the action of an
agonist, thereby preventing a response. It has high affinity, but low efficacy as it does
not produce the normal response of that receptor.
Not all drugs are designed to evoke a response, antagonists are an example of such
drugs.
There are two types of antagonists:
- Competitive (reversible) antagonists
- Non-competitive antagonists
Competitive (reversible) antagonists
A reversible antagonists does not produce a direct biological effect when it binds to a
receptor, instead it competes with an agonist that would bind to that same receptor
(therefore it is a competitive antagonist)
Reversible antagonists reduce the ability of an agonist to produce a full response
The extent of antagonism depends on relative amounts of agonist and antagonist as
increasing the amount of agonist can overcome the blocking effect of a fixed amount
of competitive antagonist, and a full response can be restored. (This is why it is
reversible)
An antagonist reduces the potency of the agonist, so a bigger dose of the agonist is
required to achieve the same maximal response.
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