Pharmacology Pharmacodynamics and Mechanism of Action 2 — Questions and Answers
Question 1: A drug with an EC50 of 2 nM is compared to one with an EC50 of 20 nM. Which statement is correct?
- The 20 nM drug is more potent
- The 2 nM drug is more potent (Correct answer)
- Both drugs have equal potency
- EC50 measures efficacy, not potency
Correct answer: The 2 nM drug is more potent
A lower EC50 means less drug is needed to achieve half-maximal effect, indicating greater potency.
Question 2: Which receptor mechanism involves a ligand-gated ion channel that opens within milliseconds of agonist binding?
- Type II (metabotropic)
- Type IV (nuclear receptor)
- Type I (ionotropic) (Correct answer)
- Type III (tyrosine kinase)
Correct answer: Type I (ionotropic)
Type I (ionotropic) receptors are ligand-gated ion channels that produce rapid responses within milliseconds.
Question 3: A drug that binds to an allosteric site and enhances agonist binding without activating the receptor itself is called a:
- Competitive antagonist
- Positive allosteric modulator (Correct answer)
- Inverse agonist
- Partial agonist
Correct answer: Positive allosteric modulator
A positive allosteric modulator potentiates agonist-induced receptor activation by binding to a site distinct from the orthosteric site.
Question 4: Which phenomenon describes the decreased response to a drug after repeated dosing due to receptor internalization?
- Sensitization
- Synergism
- Down-regulation (Correct answer)
- Supersensitivity
Correct answer: Down-regulation
Down-regulation refers to the decrease in receptor number or sensitivity following prolonged agonist exposure, often via receptor internalization.
Question 5: The Schild equation is used to characterize which type of drug interaction?
- Non-competitive antagonism
- Pharmacokinetic drug interactions
- Competitive antagonism (Correct answer)
- Irreversible agonism
Correct answer: Competitive antagonism
The Schild equation quantifies competitive antagonism by relating the dose ratio to antagonist concentration, yielding the pA2 value.
Question 6: A drug produces a maximal response of only 60% compared to a full agonist at the same receptor. This drug is best described as:
- A competitive antagonist
- A partial agonist (Correct answer)
- A pharmacological antagonist
- A neutral antagonist
Correct answer: A partial agonist
A partial agonist produces a submaximal response (less than 100% efficacy) even when all receptors are occupied.
Question 7: Which second messenger is directly produced by adenylyl cyclase activation following Gs protein stimulation?
- Inositol trisphosphate (IP3)
- Diacylglycerol (DAG)
- Cyclic AMP (cAMP) (Correct answer)
- Cyclic GMP (cGMP)
Correct answer: Cyclic AMP (cAMP)
Gs protein activation stimulates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), the primary second messenger in this pathway.
Pharmacology Pharmacodynamics and Mechanism of Action 2
A drug with an EC50 of 2 nM is compared to one with an EC50 of 20 nM.
Which statement is correct?