Pharmacology Pharmacodynamic Mechanisms Questions and Answers

Question 1

A partial agonist is administered to a patient who is already taking a full agonist for the same receptor. What is the expected pharmacodynamic effect of adding the partial agonist?

Accepted Answer

The partial agonist will act as a competitive antagonist, reducing the effect of the full agonist.

Answer

A synergistic effect, leading to a response greater than the full agonist alone.

Answer

No change in the overall effect, as the full agonist will completely override the partial agonist.

Answer

An additive effect, where the total response is the sum of the individual effects of both drugs.

Question 2

A patient experiences a rapidly diminishing response to a drug after only a few doses administered over a short period. This phenomenon, often due to the depletion of an endogenous substance, is best described as:

Accepted Answer

Tachyphylaxis

Answer

Tolerance

Answer

An idiosyncratic reaction

Answer

Pharmacokinetic antagonism

Question 3

Which of the following describes the mechanism of a non-competitive antagonist?

Accepted Answer

It binds to an allosteric site on the receptor, changing the receptor's conformation and preventing agonist activation.

Answer

It binds to the same site as the agonist, and its effect can be overcome by increasing the agonist concentration.

Answer

It produces an effect opposite to that of the agonist by binding to the same receptor.

Answer

It enhances the binding affinity of the agonist for the receptor, leading to an exaggerated response.

Question 4

A drug is found to decrease the basal activity of a receptor that is constitutively active (active even in the absence of a ligand). This drug is best classified as a(n):

Accepted Answer

Inverse agonist

Answer

Full agonist

Answer

Neutral antagonist

Answer

Partial agonist

Question 5

The activation of a G-protein coupled receptor (GPCR) by an agonist typically initiates a signaling cascade that involves which of the following key steps?

Accepted Answer

Exchange of GDP for GTP on the alpha subunit of the associated G-protein.

Answer

Direct opening of an ion channel integrated within the receptor structure.

Answer

Binding of the agonist-receptor complex to DNA to alter gene transcription.

Answer

Activation of an intracellular kinase domain that autophosphorylates.

Question 6

A new drug has a therapeutic index (TI) of 2.0, calculated as the ratio of the TD50 to the ED50. How should this information be interpreted from a clinical safety perspective?

Accepted Answer

The drug has a narrow therapeutic window, requiring careful patient monitoring to avoid toxicity.

Answer

The drug is extremely safe with a wide margin between effective and toxic doses.

Answer

The effective dose is twice the toxic dose, indicating a high risk of therapeutic failure.

Answer

The therapeutic index cannot be used to assess the safety of a drug.