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ACEM PRIMARY VIVA: PHARMACOLOGY - PHARMACOKINETICS/ PHARMACODYNAMICS EXAM 2024/2025
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ACEM PRIMARY VIVA: PHARMACOLOGY - PHARMACOKINETICS/ PHARMACODYNAMICS EXAM 2024/2025
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ACEM PRIMARY VIVA: PHARMACOLOGY - PHARMACOKINETICS/PHARMACODYNAMICS EXAM 2024/2025
What is an antagonist? - Precise Answer ✔✔Receptor antagonists bind
to receptors but do not activate them. The primary action of antagonists
is to prevent agonists from activating receptors.
What is the difference between a competitive and non-competitive
antagonist? - Precise Answer ✔✔Competitive antagonist: in the
presence of a fixed concentration of agonist, increasing concentrations
of a reversible competitive antagonist progressively inhibit the agonist
response. High antagonist concentrations inhibit the response
completely. High agonist concentrations can still evoke maximal
response
- e.g. naloxone and heroin
- e.g. propanolol and noradrenaline/ adrenaline
- e.g. flumazenil, isoprenaline, naltrexone, nalmefene
Non-competitive (aka irreversible) antagonist: bind via covalent bonds
or just bind so tightly that the receptor is unavailable for the agonist.
Number of receptors available may then be too low to allow maximal
response regardless of agonist concentration. Duration of action depends
on rate of turnover of receptor antagonist molecules rather than
elimination of the antagonist.
- e.g. phenoxybenzamine and adrenaline
- e.g. MAOI
, What effect does a competitive agonist have on the concentration-effect
curve? - Precise Answer ✔✔Shift agonist vs effect curve to right.
Higher concentrations of agonist can overcome competitive antagonist.
What is the difference between potency and efficacy? - Precise Answer
✔✔POTENCY is the amount of drug required to produce an effect. It is
dependent on the affinity of drug for receptor as well as the number of
receptors available. A good measure of potency is the EC50 - the
concentration that produces 50% of the maximal response.
(NB ED50 is the dose that produces 50% of the maximal response)
- Example: fentanyl is 100x more potent than morphine (0.1mg fentanyl
= 10mg morphine)
EFFICACY is the maximum response that a drug (agonist) can produce
(Emax) when all receptors are occupied, irrespective of the
concentration required to produce that response (irrespective of dose).
Efficacy determines the drug's clinical effectiveness and reflects the
response axis.
Draw a concentration-response curve showing 2 drugs with the same
potency but different efficacy. - Precise Answer ✔✔
Draw and explain a dose-response curve for an agonist - Precise Answer
✔✔Non logarithmic scale
Logarithmic scale
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