Pharma - Berto - L2 part 1

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Questions and Answers

What effect do competitive antagonists have on the dose-response curve of an agonist?

It shifts the curve to the left.

It shifts the curve downward.

It shifts the curve to the right. (correct)

It alters the maximum effect of the agonist.

Which statement is true regarding non-competitive antagonists?

They compete directly with agonists for binding.

They affect the maximum effect (Emax) without changing Kd. (correct)

They increase the affinity of the agonist for the receptor.

They bind irreversibly to the agonist's active site.

In the double reciprocal plot for competitive antagonists, what happens to the x-axis intersection as the dose of antagonist increases?

It moves closer to Kd.

It moves closer to zero. (correct)

It remains constant.

It shifts further away from zero.

What differentiates a competitive antagonist from a non-competitive antagonist in terms of interaction with agonists?

Non-competitive antagonists do not compete with the agonist. Signup and view all the answers

When a non-competitive antagonist is introduced, what aspect of the dose-response curve is primarily affected?

The maximum effect (Emax). Signup and view all the answers

What happens to the intersection point in a double reciprocal plot for non-competitive antagonists?

It shifts along the y-axis. Signup and view all the answers

In the context of competitive antagonism, what happens to the apparent Kd as inhibitor concentration increases?

It increases proportionally. Signup and view all the answers

What is the significance of pA2 in the context of the Schild equation?

It represents the negative logarithm of the inhibitor concentration. Signup and view all the answers

Which statement is true regarding the interaction of non-competitive antagonists with receptors?

They interact at an allosteric site without affecting agonist affinity. Signup and view all the answers

How is drug potency generally compared between two drugs?

By comparing EC50 values. Signup and view all the answers

What distinguishes efficacy from potency in pharmacology?

Efficacy is the maximum response a drug can achieve. Signup and view all the answers

What is an important conclusion about drugs with the same potency?

They may achieve different maximum effects. Signup and view all the answers

What is intrinsic activity as it relates to agonists and antagonists?

It indicates the drug's ability to activate a receptor. Signup and view all the answers

In what scenario would a competitive antagonist's effects be most pronounced?

When the agonist concentration is significantly higher. Signup and view all the answers

How does the concentration of a competitive antagonist influence its degree of inhibition?

It directly relates to the degree of inhibition. Signup and view all the answers

Study Notes

Antagonism

Competitive antagonists shift agonist dose-response curves to the right; higher agonist doses are needed for the same effect.
Non-competitive antagonists do not change the affinity of the agonist but decrease the maximum effect (Emax) without affecting Kd.
Non-competitive antagonists can interact irreversibly at the agonist's binding site or act as allosteric modulators at different binding sites.

Dose-Response Curves

In double reciprocal plots, competitive antagonists show a shift in intersection with the x-axis, indicating changes in Kd, while y-axis intersection (1/Emax) remains constant.
Non-competitive antagonists affect the y-axis intersection (1/Emax) and not the x-axis (Kd), indicating no change in affinity.

Competitive Antagonism

The presence of a competitive antagonist modifies the equilibrium formula for receptor-ligand interactions, leading to an apparent increase in Kd.
The Schild equation is used to determine if an antagonist is competitive. When the antagonist's concentration is double that of the ligand, pA2 = -log Ki indicates relative affinity.

Non-Competitive Antagonism

Non-competitive antagonists interact without affecting agonist affinity; hence, IC50 equals Ki.
The maximum effect decreases, whereas the affinity remains unchanged.

Potency

Potency defines a drug's effectiveness concerning lower doses needed to achieve the same effect compared to others; measured by Kd or EC50.
In vitro potency correlates with receptor affinity, but in vivo factors like tolerance and metabolism can alter this relationship.

Efficacy

Efficacy refers to the maximum response achievable by a drug; high potency does not imply high efficacy.
Clinical relevance often prioritizes efficacy over potency; effective, less potent drugs may be preferred in therapy.

Intrinsic Activity/Efficacy Theory

Agonists possess intrinsic activity (α) influencing efficacy;
- Full agonists α = 1,
- Partial agonists 0 < α < 1,
- Inverse agonists α < 0.
Antagonists have no intrinsic activity (α = 0) and cannot trigger a response.
Partial agonists can shift curves like competitive antagonists and stabilize inactive receptor states like inverse agonists.

Agonist-Antagonists or Partial Agonists

Partial agonists display both agonist and antagonist properties; they compete with full agonists at lower effect levels.
Their intrinsic activity generally falls between 0.2 and 0.3, affecting agonist potency similarly to competitive antagonists.

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Description

This quiz covers the key concepts of pharmacodynamics, focusing on dose-response curves and the behavior of different types of drugs, including antagonists and agonists. The importance of quantal curves and therapeutic index will also be discussed. Test your knowledge on competitive and non-competitive antagonism.