Pharmacology Basics – Nursing and Allied Health – Core Concepts and Study Guide
What factor below is LEAST likely to influence a drug's effect on a patient when taken orally?
Response
A) Molecular size
B) Molecular shape
C) Physical state or phase
D) Ability to form covalent bonds
E) Concentration - correct answer Explanation
D) Ability to form covalent bonds.
Most receptor interactions are not covalent rather electrostatic drug-receptor interactions are
much more common.
An integral component of any drugs action is its ability to reach its target site of action and then
bind to a receptor target. The pharmacokinetic factors, absorption and distribution, as well as
the pharmacodynamic effects on the receptor are greatly influence by the physical
characteristics of a drug. For example, a majority of drugs are in the 100-1000 MW range--
smaller fit tightly into receptor pockets and are not diffusion limited like larger molecules. The
molecular shape is important to provide specificity of binding to the receptor pocket. The
physical state (gas, liquid, or solid) determines route of delivery. Obviously gasses must be
inhaled. Ficks law indicates that the amount of drug moving across compartments is dependent
on the concentration gradient driving the molecules.
A weak acid drug (A), with a pKa = 6, is given orally. Assuming that the pH of the stomach equals
3 and the pH of the blood equals 7, which of the following statements is true?
Response
A) At equilibrium, there is roughly 1000 times more dissociated drug than undissociated drug in
the stomach
B) At equilibrium, the ratio of dissociated to undissociated drug in the blood is approximately
10
C) At equilibrium, 10 times more undissociated drug than dissociated drug is in the blood
D) Drug concentrations on the blood side of the stomach barrier will never reach the
concentration of drug in the stomach
,Pharmacology Basics – Nursing and Allied Health – Core Concepts and Study Guide
E) The drug will be more rapidly excreted if the urine is made acidic - correct answer
Explanation: B) At equilibrium, the ratio of undissociated to dissociated drug in the blood is
approximately 10
log (protonated/unprotonated) = pKa- pH
Weak acids when bound to hydrogen have no charge (lipid soluble). When ionized, dissociated
from H+ ion, they are charged (water soluble)
The opposite for weak bases
Weak bases when bound to hydrogen have a positive charge (water soluble)
When dissociated from H+ ion they lose charge (lipid soluble)
According to the Henderson-Hasselbalch equation, with respect to weak acids the pK equals the
pH when the log of the ratio of ionized (unprotonated or dissociated) and protonated
(undissociated) forms is 0 (i.e., their concentrations are equal and have a ratio of 1). When the
pH of a solution (blood) is 7 and the pK of the acid is 6, at equilibrium, the log of the ratio of the
concentrations of ionized form to protonated form is 1 (i.e., there is 10 times more ionized than
protonated acid in the blood). When the pH of a solution (stomach) is 3 and the pK of the acid is
6, log of the ratio of the concentrations of the ionized to protonated forms is -3 (i.e., the
concentration of the ionized form is 1/1000 that of the protonated form, meaning that there is
1000 times more protonated than ionized acid). Drug will accumulate in the compartment in
which it is more highly charged (ion-trapping)—in this case, the blood. Acidification of the urine
will increase the protonation of an acid and increase reabsorption, thereby slowing renal
excretion.
Cocaine is a weak base, with a pKa of 8.5. Which statement is true? Assume the pH of the
stomach equals approximately 3.5 and the pH of blood equals approximately 7.5.
Responses
A) The unprotonated form of cocaine will predominate under stomach pH conditions
B) There should be a 50 to 50 ratio of protonated to unprotonated cocaine in the stomach
C) The ratio of unprotonated to protonated forms of cocaine in the stomach is 10 to 1
D) Making the urine more basic should accelerate excretion
, Pharmacology Basics – Nursing and Allied Health – Core Concepts and Study Guide
E) The ratio of charged to uncharged cocaine in the stomach is 100,000 to 1 - correct answer
Explanation: C) The ratio of charged to uncharged cocaine in the stomach is 100,000 to 1
Using HH equation: log p/unP = pKa-pH or 8.5 - 3.5 = Log P/unP = 5 or when converted to the
ratio of p/unP is 100,000 to 1. Thus indicating that in the stomach the protonated (charged
form because it is a weak base) will be predominant. This is also a reason why drug abuser tend
to avoid oral administration of cocaine. A 50/50 ratio is achieved when the pKa = pH. The other
ratios described are incorrect. A simple rule to follow is that if you want to increase excretion of
a weak base make the urine more acidic and vice versa for a weak acid.
Which statement is true regarding weak-drug-receptor bonding (electrostatic or hydrophobic)
and strong-drug-receptor bonding (covalent)?
A. Drugs that bind to receptors through covalent bonds have a shorter duration of action
B. Drugs that form covalent bonds are not used in medicine
C. Most drugs form covalent bonds with their target receptors
D. Strong-bonding-drugs require a more precise fit into receptor pockets as compared to weak-
bonding drugs
E. Weak-bonding drugs tend to be more receptor-selective than strong-bonding drugs - correct
answer answer: E. Weak-bonding drugs tend to be more receptor-selective than strong-
bonding drugs
Drugs with weak bonding (electrostatic or hydrophobic) properties are more common. This
type of bonding requires a more selective association with the drug and receptor pocket.
Drugs that form covalent bonds (e.g. Aspirin or phenoxybenzamine) produce effects that last
for the life of the enzyme or receptor they bond to. This type of interaction is less favorable in
clinical medicine. It is more common for a useful drug to be able to come on and off the
receptor readily.
Which of the following physical properties of a drug is most consistent with a drug that has
good oral bioavailability?
A. A drug that has many negative charges (e.g. heparin)
What factor below is LEAST likely to influence a drug's effect on a patient when taken orally?
Response
A) Molecular size
B) Molecular shape
C) Physical state or phase
D) Ability to form covalent bonds
E) Concentration - correct answer Explanation
D) Ability to form covalent bonds.
Most receptor interactions are not covalent rather electrostatic drug-receptor interactions are
much more common.
An integral component of any drugs action is its ability to reach its target site of action and then
bind to a receptor target. The pharmacokinetic factors, absorption and distribution, as well as
the pharmacodynamic effects on the receptor are greatly influence by the physical
characteristics of a drug. For example, a majority of drugs are in the 100-1000 MW range--
smaller fit tightly into receptor pockets and are not diffusion limited like larger molecules. The
molecular shape is important to provide specificity of binding to the receptor pocket. The
physical state (gas, liquid, or solid) determines route of delivery. Obviously gasses must be
inhaled. Ficks law indicates that the amount of drug moving across compartments is dependent
on the concentration gradient driving the molecules.
A weak acid drug (A), with a pKa = 6, is given orally. Assuming that the pH of the stomach equals
3 and the pH of the blood equals 7, which of the following statements is true?
Response
A) At equilibrium, there is roughly 1000 times more dissociated drug than undissociated drug in
the stomach
B) At equilibrium, the ratio of dissociated to undissociated drug in the blood is approximately
10
C) At equilibrium, 10 times more undissociated drug than dissociated drug is in the blood
D) Drug concentrations on the blood side of the stomach barrier will never reach the
concentration of drug in the stomach
,Pharmacology Basics – Nursing and Allied Health – Core Concepts and Study Guide
E) The drug will be more rapidly excreted if the urine is made acidic - correct answer
Explanation: B) At equilibrium, the ratio of undissociated to dissociated drug in the blood is
approximately 10
log (protonated/unprotonated) = pKa- pH
Weak acids when bound to hydrogen have no charge (lipid soluble). When ionized, dissociated
from H+ ion, they are charged (water soluble)
The opposite for weak bases
Weak bases when bound to hydrogen have a positive charge (water soluble)
When dissociated from H+ ion they lose charge (lipid soluble)
According to the Henderson-Hasselbalch equation, with respect to weak acids the pK equals the
pH when the log of the ratio of ionized (unprotonated or dissociated) and protonated
(undissociated) forms is 0 (i.e., their concentrations are equal and have a ratio of 1). When the
pH of a solution (blood) is 7 and the pK of the acid is 6, at equilibrium, the log of the ratio of the
concentrations of ionized form to protonated form is 1 (i.e., there is 10 times more ionized than
protonated acid in the blood). When the pH of a solution (stomach) is 3 and the pK of the acid is
6, log of the ratio of the concentrations of the ionized to protonated forms is -3 (i.e., the
concentration of the ionized form is 1/1000 that of the protonated form, meaning that there is
1000 times more protonated than ionized acid). Drug will accumulate in the compartment in
which it is more highly charged (ion-trapping)—in this case, the blood. Acidification of the urine
will increase the protonation of an acid and increase reabsorption, thereby slowing renal
excretion.
Cocaine is a weak base, with a pKa of 8.5. Which statement is true? Assume the pH of the
stomach equals approximately 3.5 and the pH of blood equals approximately 7.5.
Responses
A) The unprotonated form of cocaine will predominate under stomach pH conditions
B) There should be a 50 to 50 ratio of protonated to unprotonated cocaine in the stomach
C) The ratio of unprotonated to protonated forms of cocaine in the stomach is 10 to 1
D) Making the urine more basic should accelerate excretion
, Pharmacology Basics – Nursing and Allied Health – Core Concepts and Study Guide
E) The ratio of charged to uncharged cocaine in the stomach is 100,000 to 1 - correct answer
Explanation: C) The ratio of charged to uncharged cocaine in the stomach is 100,000 to 1
Using HH equation: log p/unP = pKa-pH or 8.5 - 3.5 = Log P/unP = 5 or when converted to the
ratio of p/unP is 100,000 to 1. Thus indicating that in the stomach the protonated (charged
form because it is a weak base) will be predominant. This is also a reason why drug abuser tend
to avoid oral administration of cocaine. A 50/50 ratio is achieved when the pKa = pH. The other
ratios described are incorrect. A simple rule to follow is that if you want to increase excretion of
a weak base make the urine more acidic and vice versa for a weak acid.
Which statement is true regarding weak-drug-receptor bonding (electrostatic or hydrophobic)
and strong-drug-receptor bonding (covalent)?
A. Drugs that bind to receptors through covalent bonds have a shorter duration of action
B. Drugs that form covalent bonds are not used in medicine
C. Most drugs form covalent bonds with their target receptors
D. Strong-bonding-drugs require a more precise fit into receptor pockets as compared to weak-
bonding drugs
E. Weak-bonding drugs tend to be more receptor-selective than strong-bonding drugs - correct
answer answer: E. Weak-bonding drugs tend to be more receptor-selective than strong-
bonding drugs
Drugs with weak bonding (electrostatic or hydrophobic) properties are more common. This
type of bonding requires a more selective association with the drug and receptor pocket.
Drugs that form covalent bonds (e.g. Aspirin or phenoxybenzamine) produce effects that last
for the life of the enzyme or receptor they bond to. This type of interaction is less favorable in
clinical medicine. It is more common for a useful drug to be able to come on and off the
receptor readily.
Which of the following physical properties of a drug is most consistent with a drug that has
good oral bioavailability?
A. A drug that has many negative charges (e.g. heparin)
