PCOA EXAM PRACTICE PRACTICE SCRIPT
UPDATED 2026 TESTED SOLUTIONS
⫸ Drug A is a full agonist for a specific receptor system; drug B is a
competitive antagonist for the same receptor system. If increasing doses
of drug B are co-administered with drug A, drug B will
A. increase the apparent Emax of drug A.
B. reduce the apparent Emax of drug A.
C. increase the apparent EC50 of drug A.
D. reduce the apparent EC50 of drug A Answer: C. Antagonists increase
the apparent EC50 of a drug by shifting the effect vs. concentration
curve to the right.
EC50 refers to the potency of a drug. The potency is the ability to cause
a functional change at a certain concentration. It is related to the affinity
of the drug for its receptor. A more potent drug needs a lower
concentration to cause the same functional change in a target structure.
⫸ Which of the following statements is correct for a receptor system
that exhibits a receptor reserve of 90%?
A. Partial agonists are not able to achieve maximum cellular response.
B. Only 10% of the available receptors need to be occupied by a full
agonist to achieve maximum cellular response.
C. More than 99% of the receptors need to be occupied by a competitive
antagonist to have an effect on the dose-response relationship of a full
agonist.
, D. Only 90% in the receptor reserve is available for interaction with
competitive antagonists. Answer: B. Only 10% of the available receptors
need to occupied by a full agonist to achieve maximum cellular
response.
In a system with spare receptors or receptor reserve, only a fraction of
available receptors needs to be stimulated to achieve the maximum
pharmacologic response.
⫸ EC50 is a measure of
A. the intrinsic activity of a drug.
B. the efficacy of a drug.
C. the potency of a drug.
D. the dissociation rate of a drug-receptor complex. Answer: C. The
concentration at half maximum effect, EC50, is a measure of drug
potency, The more potent a drug is, the smaller the EC50.
⫸ Which of the following can act as an antagonist for a full agonist?
A. Inverse agonist
B. Partial agonist
C. Less potent agonist
D. Noncompetitive agonist Answer: B. Partial agonist
A partial agonist can act as an antagonist for a full agonist because it
occupies the receptors but has a reduced intrinsic activity.
UPDATED 2026 TESTED SOLUTIONS
⫸ Drug A is a full agonist for a specific receptor system; drug B is a
competitive antagonist for the same receptor system. If increasing doses
of drug B are co-administered with drug A, drug B will
A. increase the apparent Emax of drug A.
B. reduce the apparent Emax of drug A.
C. increase the apparent EC50 of drug A.
D. reduce the apparent EC50 of drug A Answer: C. Antagonists increase
the apparent EC50 of a drug by shifting the effect vs. concentration
curve to the right.
EC50 refers to the potency of a drug. The potency is the ability to cause
a functional change at a certain concentration. It is related to the affinity
of the drug for its receptor. A more potent drug needs a lower
concentration to cause the same functional change in a target structure.
⫸ Which of the following statements is correct for a receptor system
that exhibits a receptor reserve of 90%?
A. Partial agonists are not able to achieve maximum cellular response.
B. Only 10% of the available receptors need to be occupied by a full
agonist to achieve maximum cellular response.
C. More than 99% of the receptors need to be occupied by a competitive
antagonist to have an effect on the dose-response relationship of a full
agonist.
, D. Only 90% in the receptor reserve is available for interaction with
competitive antagonists. Answer: B. Only 10% of the available receptors
need to occupied by a full agonist to achieve maximum cellular
response.
In a system with spare receptors or receptor reserve, only a fraction of
available receptors needs to be stimulated to achieve the maximum
pharmacologic response.
⫸ EC50 is a measure of
A. the intrinsic activity of a drug.
B. the efficacy of a drug.
C. the potency of a drug.
D. the dissociation rate of a drug-receptor complex. Answer: C. The
concentration at half maximum effect, EC50, is a measure of drug
potency, The more potent a drug is, the smaller the EC50.
⫸ Which of the following can act as an antagonist for a full agonist?
A. Inverse agonist
B. Partial agonist
C. Less potent agonist
D. Noncompetitive agonist Answer: B. Partial agonist
A partial agonist can act as an antagonist for a full agonist because it
occupies the receptors but has a reduced intrinsic activity.
