pharmocodynamics

Question 1

What are the main types of drug target in the body?

Answer 1

They’re mostly proteins divided into 4 classes:

• receptors
• enzymes
• ion channels
• transport proteins

Question 2

What is selectivity important for?

Answer 2

For a drug to be an effective therapeutic agent it must show a high degree of selectivity for a particular drug target

Question 3

Why is dose important?

Answer 3

Some drugs can bind to other receptors since the molecules that bind to them are similar in structure to the drug

If we use a high dose of a drug, it can bind to these other receptors to cause unwanted side effects

Question 4

What are the different types of drug-receptor interactions?

Answer 4

• Electrostatic interactions: most common mechanism includes hydrogen bonds and VdW forces
• Hydrophobic interactions: important for lipid soluble drugs
• Covalent bonds: least common as the interactions tend to be irreversible
• Stereospecific interactions: many drugs exist as stereoisomers and interact stereospecifically with receptors

Question 5

Explain drug-receptor complex equilibrium

Answer 5

Question 6

What is the affinity of a drug?

Answer 6

The strength of binding of the drug to the receptor

The strength of each drug-receptor complex is determined by the affinity of the drug

As a result, affinity is strongly linked to receptor occupancy

Question 7

What is the efficacy of a drug?

Answer 7

Ability of an individual drug molecule to produce an effect once bound to a receptor

Question 8

Drugs A, B, C all act on the same receptor
- Drug A binds to the receptor but doesn’t produce a response- has no efficacy
- Drug B binds to the receptor and produces a partial response, but not capable of inducing the maximal response
- Drug C binds to the receptor and produces the maximal response that could be expected from that receptor

How do drugs A, B, C work in terms of affinity and efficacy?

Answer 8

• Drug A has affinity for the receptor but no efficacy so is a receptor antagonist
• Drug B has affinity for the receptor and sub-maximal efficacy so is a partial agonist
• Drug C has affinity for the receptor and maximal efficacy so is a full agonist

Question 9

What is the potency of a drug?

Answer 9

• Conc or dose of a drug required to produce a 50% tissue response
• Standard nomenclature for this measure is the EC50 (half maximal effective conc) or the ED50 (half maximal effective dose)
• ED50 is usually used to look at the desired effect of a drug being in 50% of all individuals in a group (instead of a 50% response from 1 individual) and EC50 is usually used to see a conc of a drug that produces a 50% response
• A highly potent drug produces a large response at relatively low concs
• A highly efficacious drug can produce a maximal response and this effect is not particularly related to drug conc

Question 10

Which out of efficacy and potency is more important?

Answer 10

• Efficacy is more important- you want to know if the drug you’re giving can induce a maximal response
• If 2 drugs have equal efficacy, it doesn’t matter if 1 is more potent than the other since you can still produce the maximal response with the less potent drug (you just need to give a higher conc)