Pharmacology question

[deleted647690]

I had a question about 12. The answer was A. Doesn't the graph indicate that curve Y is less effective than curve X, since a higher concentration of drug is needed to get the same level of biological effect?

The only logical answer for me would be B, because it may be true that curve Z is less effective than curve Y because Z indicates fewer receptors on target cells, but not necessarily fewer target cells. In other words, the difference would be more properly explained as fewer receptors, rather than fewer cells themselves.

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[Hi_I'mPaul]

Some basic pharm definitions:
Efficacy = Emax (in other words maximum response)
Potency = ED50

So in this example:
A) X and Y have same Emax = same efficacy (hence why A is false, and is the correct answer)

B) True = Less target cells = less Emax (think in terms of enzyme kinetics if that helps justify. For example, what happens when we take away available enzymes for binding? We lower Vmax. Similar idea is happening here but it's in relation to a drug and it's binding cell versus a substrate and its enzyme.)

C) True = Y and Z have a higher ED50 than X so they are less potent, by definition.

D) True = Less binding sites = takes more of the drug to reach the same effect as a cell with more sites. (again, you can think of enzyme kinetics to justify if you'd like. If you have fewer receptors then you have less affinity for the substrate because there are less places to bind. More receptors = more affinity because there are simply more places to bind. How is this shown in enzyme kinetics? A decrease in affinity = a higher Km (rightward shift of the graph). This is also what we see here. A higher E50 without a change in Emax (we're not changing the total amount of cells here).)

With your logic for answer B, a decrease in receptors should show a rightward shift without a change in Emax (similar to the change from X to Y).

I wrote this quickly so I hope it makes sense and I didn't make an error.

Hope this helps!

 

[deleted647690]

Some basic pharm definitions:
Efficacy = Emax (in other words maximum response)
Potency = ED50

So in this example:
A) X and Y have same Emax = same efficacy (hence why A is false, and is the correct answer)

B) True = Less target cells = less Emax (think in terms of enzyme kinetics if that helps justify. For example, what happens when we take away available enzymes for binding? We lower Vmax. Similar idea is happening here but it's in relation to a drug and it's binding cell versus a substrate and its enzyme.)

C) True = Y and Z have a higher ED50 than X so they are less potent, by definition.

D) True = Less binding sites = takes more of the drug to reach the same effect as a cell with more sites. (again, you can think of enzyme kinetics to justify if you'd like. If you have fewer receptors then you have less affinity for the substrate because there are less places to bind. More receptors = more affinity because there are simply more places to bind. How is this shown in enzyme kinetics? A decrease in affinity = a higher Km (rightward shift of the graph). This is also what we see here. A higher E50 without a change in Emax (we're not changing the total amount of cells here).)

With your logic for answer B, a decrease in receptors should show a rightward shift without a change in Emax (similar to the change from X to Y).

I wrote this quickly so I hope it makes sense and I didn't make an error.

Hope this helps!

Thanks. They do have different potencies then. I didn't know the difference between efficacy and potency.