Pharmacology Pharmacodynamics 3 — Questions and Answers
Question 1: A drug produces the same maximum effect as morphine but requires a 10-fold higher dose. This drug has:
- Lower efficacy than morphine
- Lower potency but equal efficacy compared to morphine (Correct answer)
- Higher potency than morphine
- Lower intrinsic efficacy than morphine
Correct answer: Lower potency but equal efficacy compared to morphine
Potency refers to the dose required for a given effect; since this drug requires more drug for the same Emax, it is less potent but equally efficacious.
Question 2: Which receptor type uses a JAK-STAT intracellular signaling pathway?
- G-protein coupled receptors
- Ligand-gated ion channels
- Cytokine/growth factor receptors (Correct answer)
- Nuclear receptors
Correct answer: Cytokine/growth factor receptors
Cytokine receptors (e.g., for interferons, erythropoietin) lack intrinsic kinase activity but associate with Janus kinases (JAKs) that activate STAT transcription factors.
Question 3: When two drugs are combined and the effect equals the sum of their individual effects, this is called:
- Potentiation
- Synergism
- Additive effect (Correct answer)
- Antagonism
Correct answer: Additive effect
An additive effect occurs when the combined effect of two drugs equals the arithmetic sum of their individual effects, as if each drug contributes independently.
Question 4: Spare receptors (receptor reserve) exist when:
- Emax requires occupation of all available receptors
- Maximal effect is achieved with less than full receptor occupancy (Correct answer)
- The drug has low affinity for the receptor
- The EC50 equals the Kd
Correct answer: Maximal effect is achieved with less than full receptor occupancy
Spare receptors exist when Emax is reached at concentrations that occupy only a fraction of available receptors, meaning receptor number exceeds what is needed for maximum response.
Question 5: Phenoxybenzamine is an example of which type of antagonist?
- Competitive reversible antagonist
- Physiological antagonist
- Irreversible (non-competitive) antagonist (Correct answer)
- Partial agonist acting as antagonist
Correct answer: Irreversible (non-competitive) antagonist
Phenoxybenzamine covalently and irreversibly alkylates alpha-adrenergic receptors, permanently blocking them and reducing Emax rather than just shifting the dose-response curve.
Question 6: The Hill equation describes the relationship between drug concentration and effect. A Hill coefficient (n) greater than 1 indicates:
- Simple one-to-one drug-receptor binding
- Positive cooperativity in ligand binding (Correct answer)
- Negative cooperativity
- Competitive antagonism
Correct answer: Positive cooperativity in ligand binding
A Hill coefficient >1 indicates positive cooperativity, meaning binding of one drug molecule increases the affinity of subsequent binding, producing a steeper sigmoidal dose-response curve.
Question 7: Which second messenger is generated when Gq-coupled receptors are activated?
- cAMP
- cGMP
- Inositol trisphosphate (IP3) and diacylglycerol (DAG) (Correct answer)
- Arachidonic acid
Correct answer: Inositol trisphosphate (IP3) and diacylglycerol (DAG)
Gq proteins activate phospholipase C-β, which cleaves PIP2 into IP3 (triggering intracellular Ca2+ release) and DAG (activating protein kinase C).
Pharmacology Pharmacodynamics 3
A drug produces the same maximum effect as morphine but requires a 10-fold higher dose.
This drug has: