Pharmacodynamics - Pt. 1
Questions and Answers
- 1.
Which of the following cell constituents most likely function as drug receptors?
- A.
G-proteins
- B.
Ion channel proteins
- C.
Cyclic AMP
- D.
Membrane lipids
- E.
Water molecules
Correct Answer
B. Ion channel proteinsExplanation
1) Learning objective: describe the main cell constituents that can act as drug receptors.
Answer: B
Ion channel proteins can function as receptors, since binding to those channels may cause the
opening of the channel (i.e. acetylcholine at nicotinic receptors). It is worth to note that, in this
case, the receptor is also the effector because a single molecule incorporates both the drug
binding site and the effector mechanism.
A) G-proteins are not receptors. They are coupled to many receptors and the activation of those
receptors in turn activates the G-protein.
C) cAMP is a second messenger, i.e a molecule that transmits and amplify signals received from
the receptor.
D, E ) Receptors are most often protein molecules.Rate this question:
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- 2.
Which of the following terms best describes a specific region of the receptor molecule where the drug binds?
- A.
Activation region
- B.
Recognition site
- C.
Effector
- D.
G-protein
- E.
Spare receptor
Correct Answer
B. Recognition siteExplanation
2) Learning objective: define the specific region of the receptor molecule at which the drug
binds.
Answer: B
Drugs acting on receptors bind to a specific region of the receptor molecule called receptor site
or, better, recognition site. In fact this is the region that has a high and selective affinity for the
drug and therefore can bind the drug with a chemical bond.
A) There is no activation region since the site of receptor molecule can bind the drug, but then
the drug can either activate or block the receptor.
C) Effectors are molecules that translate the drug-receptor interaction into a biological effect.
D) G-proteins are not part of the receptor but are separate proteins that can be activated by an
activated receptor.
E) Spare receptors are receptors that are not occupied by the drug even when a maximal
response is obtained.Rate this question:
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- 3.
A new drug was tested in an in vitro system. It was found that only one enantiomer of the racemic pair bound substantially to a specific receptor, whereas the other enantiomer showed a negligible binding. Which of the following terms best defines this property?
- A.
Intrinsic activity
- B.
Affinity
- C.
Stereo-selectivity
- D.
Potency
- E.
Variability
- F.
Maximal efficacy
Correct Answer
C. Stereo-selectivityExplanation
3) Learning objective: define the term stereo-selectivity
Answer: C
A peculiar property of receptors is stereo-selectivity, that is often they bind only one enantiomer
of a racemic pair.
A) Intrinsic activity refers to the ability of a drug (once bound to a receptor) to initiate changes
which lead to a biological response.
B) Affinity refers to the tendency of a drug to bind to a receptor.
D) Potency refers to the dose of a drug required to produce a given effect.
E) Variability refers to the fact that the number of receptors can vary with time.
F) Maximal efficacy refers to the maximal effect that can be produced by a drugRate this question:
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- 4.
A 16-year-old girl suffering from seasonal rhinitis started a therapy with loratadine, a drug that binds to H1 histamine receptors. Which of the following terms best defines the intrinsic ability of a drug to bind to a receptor?
- A.
Intrinsic activity
- B.
Potency
- C.
Efficacy
- D.
Affinity
- E.
Receptor activation
Correct Answer
D. AffinityExplanation
4) Learning objective: define the term “affinity” of a drug.
Answer: D
The tendency of a drug to bind to a receptor is defined affinity. According to the occupation
theory binding to a receptor is driven by the law of mass action, that is the number of bound
receptors increases when the number of available drug molecules increases. Now suppose that
100 receptors are exposed to 1000 molecules of drug A or to 1000 molecules of drug B. Also
suppose that 10 molecules of drug A are able to bind to the receptors, but 40 molecule of drug B
are able to bind to the receptors. It can be concluded that receptor affinity of drug B is greater
than that of drug A.
A) Intrinsic activity refers to the ability of a drug (once bound to a receptor) to initiate changes
which lead to a biological response.
B) Potency refers to the dose of a drug required to produce a given effect (often the effect is
chosen as the 50% of drug's maximal effect). The lower the dose required to produce the effect,
the higher the potency
C) Efficacy refers to the maximal effect that can be produced by a drug.
E) Receptor activation is related to the drug intrinsic activity (the higher the intrinsic activity of a
drug , the higher the amount of receptor activation brought about by that drug).Rate this question:
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- 5.
Drugs can bind to receptors via different types of chemical bonds. Which of the following is the least common drug-receptor bond?
- A.
Ionic
- B.
Hydrophobic
- C.
Hydrogen
- D.
Van der Waals
- E.
Covalent
Correct Answer
E. CovalentExplanation
5) Learning objective: describe the different drug -receptor bonds.
Answer: E
In general drugs binding to receptors in a reversible way and therefore the chemical bond
between drug and receptor must be weak. A covalent bond is the strongest chemical bond (more
than 50 Kcal/mole) and is rare in pharmacology. Nevertheless some drugs can bind covalently
and this often results in an irreversible action (examples are the covalent bond between some
anticancer drugs and the DNA, between phenoxybenzamine and alpha receptors, between
organophosphates and cholinesterase).
A, B, C, D) The energy of all these chemical bonds is less than 10 Kcal/mole.Rate this question:
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- 6.
Two new drugs, A and B, are tested in an in vitro system. The drugs turn out to have the same slope of the log dose-response curves and the same maximal efficacy. Which of the following pairs of statements best describes drugs A and B?
- A.
A full agonist , B full agonist
- B.
A full agonist , B partial agonist
- C.
A full agonist , B competitive antagonist
- D.
A partial agonist, B noncompetitive antagonist
- E.
A partial agonist, B functional antagonist
Correct Answer
A. A full agonist , B full agonistExplanation
6) Learning objective: explain why log dose- response curves can indicate the tipe of drugreceptor
interaction
Answer: A
When two drugs exhibit the same slope of the dose response curves the drugs most likely act at
the same receptor. Since they have the same maximal efficacy both drugs must be full agonists. .
B; C; D, E) (see explanation above)Rate this question:
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- 7.
Which of the following terms best defines a drug with intrinsic activity higher than 0% and lower than 100%?
- A.
Full agonist
- B.
Pharmacological antagonist
- C.
Partial agonist
- D.
Functional antagonist
- E.
Chemical antagonist
Correct Answer
C. Partial agonistExplanation
7) Learning objective: define the term “partial agonist”.
Answer: C
A drug which is able to activate only partially the receptor is defined a partial agonist. This
means that its intrinsic activity is higher than 0% and lower than 100%. Therefore when all
receptors in a system are activated by a partial agonist, the maximum effect of the drug will be
lower than the one produced by a full agonist, that is the maximal efficacy of a partial agonist is
by definition lower than that of a full agonist.
A) The intrinsic activity of a full agonist is by definition 100%.
B) The intrinsic activity of a pharmacological antagonist is by definition 0%.
D, E) These antagonisms are not related to the receptor theory and therefore they cannot be
related to the intrinsic activity.Rate this question:
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- 8.
Two drugs, tested in an in vitro system, turn out to have equal affinity for the same receptor and intrinsic activities of 1.0 and 0.25 respectively. Which of the following would be the correct percent of the maximal response, when both drugs are present at the same time in maximally effective concentrations?
- A.
12.5%
- B.
25%
- C.
62.5%
- D.
75%
- E.
100%
Correct Answer
C. 62.5%Explanation
8) Learning objective: calculate the response of two drugs present together in an in vitro
system, given sufficient data.
Answer: C
Since the two drugs have equal affinity for the same receptor, when both are present at the same
time in maximally effective concentrations, one half of the receptors will be occupied by the first
drug and one half by the second drug. Since the intrinsic activity of the first drug is 1.0, each
receptor occupied by this drug will be activated 100% and therefore the total response of one
half of the receptors will be 50% of the maximal response. By the same token, since the intrinsic
activity of the second drug is 0.25, each receptor occupied by this drug will be activated 25% and
so the total response of the other half of the receptors will be 12.5% of the maximal response.
Therefore the response of all receptors will be 50% +12.5%, that is 62.5 % of the maximal
response.
A, B, D, E) (see explanation above)Rate this question:
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- 9.
Five new diuretic drugs were tested in healthy volunteers. The results are given below: Which of the following drugs was the most effective?
- A.
Drug A
- B.
Drug B
- C.
Drug C
- D.
Drug D
- E.
Drug E
Correct Answer
D. Drug DExplanation
9) Learning objective: define the terms potency and efficacy of a drug.
Answer: D
Drug effectiveness is measured by the maximal effect the drug can produce when the dose is
taken to high levels. In case of diuretics the maximal daily urine output (that is the urine output
that is no longer increased by increasing the dose) is a convenient measure of the effectiveness
of the drug. It is worth to note that efficacy is independent upon potency, which is measured by
the drug needed to get 50% of maximal effect. In fact in the present case the drug D is the most
effective but the least potent.
A, B, C, E) (see explanation above)Rate this question:
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- 10.
Drug A and Drug B, tested in an in vitro system, turn out to have equal affinity for the same receptor and intrinsic activities greater than zero. The maximal efficacy of drug B is 100%. When Drug B is co-administered with a fixed dose of Drug A, the log dose-effect curve of Drug B is shifted to the right. Which of the following terms best defines drug A?
- A.
Full agonist
- B.
Partial agonist
- C.
Competitive antagonist
- D.
Irreversible antagonist
- E.
Functional antagonist
Correct Answer
C. Competitive antagonistExplanation
Competitive antagonist fits best because these drugs bind to the same receptor as the agonist (Drug B) without activating them, and can be displaced by increasing concentrations of the agonist. This causes a rightward shift in the dose-response curve of the agonist, indicating that a higher concentration of the agonist is needed to achieve the same effect, due to competition at the receptor site.Rate this question:
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- 11.
A 3-year-old boy was admitted to the emergency room after e generalized tonic colonic seizure. His mother reported that the boy apparently ingested several tablets of propranolol (a beta-blocking drug) found in his father drawer. The boy received an IM injection of glucagon, a hormone that can bind to glucagon receptors in the heart, so causing a significant increase in heart contractility. In this way It can counteract the decrease in heart contractility brought about by a toxic dose of a beta-blocker. Which of the following terms best defines the antagonism between glucagon and beta-blockers?
- A.
Chemical
- B.
Competitive
- C.
Functional (or physiological)
- D.
Pharmacokinetic
- E.
Pharmacological
Correct Answer
C. Functional (or pHysiological)Explanation
11) Learning objective: define the term “functional antagonism”.
Answer: C
Glucagon induced activation of glucagon receptors leads to an increase in heart contractility. By
blocking beta-1 receptors in the heart beta-blockers lead to a decrease in heart contractility.
When two drugs act on different receptors causing action in opposite directions, the antagonism
is defined functional (also called physiological).
A, B, D, E) (see explanation above)Rate this question:
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- 12.
The figure below, depicts the log dose-response curves of different drugs tested in an in vitro system where no spare receptors are present . Which of the curves best depicts the log dose-response curve of drug C when a fixed dose of an irreversible antagonist is given concomitantly?
- A.
Curve A
- B.
Curve B
- C.
Curve C
- D.
Curve D
- E.
Curve E
Correct Answer
D. Curve DExplanation
12) Learning objective: predict the shape of log-dose effect curve of an agonist when afixed
dose of irreversible antagonist is given concomitantly.
Answer: D
Irreversible antagonists bind to the receptor so tightly that the receptor is unavailable for binding
of agonist. After occupancy of some proportion of receptors by such an antagonist, the number
of remaining unoccupied receptors may be to low for the agonist(even at high concentrations) to
elicit a response comparable to the previous maximal response. Therefore an irreversible
antagonist will cause a downward shift of the maximum of the log dose effect curve, i.e. from C to
D.
A, B, C, E) (see explanation above)Rate this question:
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- 13.
A 65-year-old woman, admitted to the hospital with a myocardial infarction, developed a ventricular tachicardia and received an IV injection of lidocaine. The cardiologist knew that the dose given must be within the range of doses that have a high probability of therapeutic success. Which of the following terms best defines this range?
- A.
Intrinsic activity
- B.
Efficacy
- C.
Potency
- D.
Therapeutic index
- E.
Therapeutic window
Correct Answer
E. Therapeutic windowExplanation
13) Learning objective: define the therapeutic window of a drug.
Answer: E
The interval between the minimum therapeutic dose (or plasma concentration) and the minimum
toxic dose (or plasma concentration) of a drug is defined therapeutic window. Since doses below
the minimum therapeutic dose are by definition ineffective ,and doses above the minimum toxic
dose are, by definition, toxic, this window defines the range of doses which have a high
probability of therapeutic success.
A) Intrinsic activity refers to the ability of a drug (once bound to a receptor) to initiate changes
which lead to a biological response.
B) Potency refers to the dose of a drug required to produce a given effect
C) Efficacy refers to the maximal effect that can be produced by a drug.
D) The therapeutic index is a ratio between an harmful dose and an effective dose of a drug . It
is (like the therapeutic window) an index of the safety of a drug, but is a single value and
therefore cannot predict the range of doses that are both safe and effective.Rate this question:
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- 14.
A new beta-blocker was tested in voluntary subjects. The cumulative frequency distribution of subjects showing a decrease of 10 bpm in the heart rate, was plotted against the log dose. Which of the following drug parameters can be determined from this cumulative frequency distribution?
- A.
Affinity
- B.
Median effective dose
- C.
Therapeutic index
- D.
Therapeutic window
- E.
Maximal efficacy
Correct Answer
B. Median effective doseExplanation
14)Learning objective: describe the drug parameters that can be determined from a quantal
log-doThe cumulative frequency distribution of subjects showing a desired effect is called quantal log
dose response curve. From this curve, the dose that can produce that effect in 50% of
individuals (called median effective dose) can be read on the abscissa.
A) Affinity is the tendency of a drug to bind to a receptor. It can be measured by plotting the
fraction of receptors bound by drug, against the log of the concentration of drug. It cannot be
measured with a quantal log dose-response curve.
C, D) The therapeutic index is a ratio between the toxic (TD50) and the effective (ED50) dose of a
drug. The therapeutic window is the interval between the minimum effective dose (ED1) and the
minimum toxic dose (TD1). In order to measure these variables, two quantal log dose-effect
curves are needed.
E) Maximal efficacy is the maximal effect a drug can produce. It can be measured with a grade
log dose-effect curve, but not with a quantal log dose-effect curve.se effect curveRate this question:
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- 15.
Which of the following terms best defines a drug that binds to alpha adrenergic receptors, has no intrinsic activity, and cannot be displaced by epinephrine?
- A.
Competitive antagonist
- B.
Partial agonist
- C.
Chemical antagonist
- D.
Irreversible antagonist
- E.
Functional antagonist
Correct Answer
D. Irreversible antagonistExplanation
15) Learning objective: explain the meaning of irreversible antagonist
Answer: D
Drug that can bind a receptor but has no intrinsic activity is defined pharmacological antagonist.
These antagonists can be competitive (when they can be displaced from the receptor by an
appropriate concentration of the agonist) or irreversible (when they cannot be displaced,
whatever the concentration of the agonist).
A, B, C, E) (see explanation above)Rate this question:
-
.JPG "Five new diuretic drugs were tested in healthy volunteers. The results are given below:
Which of the following drugs was the most effective?")
.JPG "The figure below, depicts the log dose-response curves of different drugs tested in an
in vitro system where no spare receptors are present . Which of the curves best depicts
the log dose-response curve of drug C when a fixed dose of an irreversible antagonist is
given concomitantly?")
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