8) Drugs, Receptors & Pharmacokinetics Flashcards
Suggest possible targets for drugs.
- Enzymes (majority)
- Receptors (GPCRs, nuclear hormone etc.)
- Ion Channels
- Transporters
Define affinity. How is it measured?
The likelihood of a ligand binding to its target receptor, measured by the Kd
Define efficacy.
The likelihood that after something binds to a receptor it’ll activate it.
Define potency. How is it measured?
A combination of both of efficacy and affinity that measures how much a concentration of a drug leads to a response which is measured by the EC50.
Why do antagonists have affinity, but not efficacy?
As they bind, however, by definition don’t cause activation.
What do we mean when we talk about spare receptors?
In some cases, less than 100% receptor occupancy will give 100% response. I.e. EC50 < Kd (50% of the maximal response takes less than 50% receptor occupancy)
What is a partial agonist?
An agonist that binds to the receptor but doesn’t elicit a full response.
Suggest a clinical use for a partial agonist with reference to the opiate withdrawl.
Buprenorphine is a partial agonist of the u-opoid receptor, with a higher affinity but lower efficacy than morphine. This can be advantageous as it displaces the morphine at the receptor and reduces the withdrawl.
What is the IC50 of a drug?
The concentration of antagonist giving 50% inhibition.
Describe the role of naloxone in respiratory depression.
High affinity, competitive antagonist at μ-opioid receptors. Used to reverse opioid mediated respiratory depression. The high affinity means it will compete effectively with other opioids (e.g. heroin) for receptors.
