Pharmacology Basics 52 CORRECTLY ANSWERED QUESTIONS LATEST UPDATE
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
A weak...
Pharmacology Basics QUESTIONS AND
ANSWERS 100% VERIFIED A+ GUARANTEED
1). 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
Ans: 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.
2). 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
e) the drug will be more rapidly excreted if the urine is made acidic
Ans: Explanation: B) At equilibrium, the ratio of undissociated to dissociated drug in the
blood is approximately 10
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, 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.
3). 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
e) the ratio of charged to uncharged cocaine in the stomach is 100,000 to 1
Ans: 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.
4). Which statement is true regarding weak-drug-receptor bonding (electrostatic or
hydrophobic) and strong-drug-receptor bonding (covalent)?
PaperStoc.com Page 2 of 19
, 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
Ans: 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.
5). 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)
b. a drug that is a quaternary amine
c. a large protein based drug (e.g. infliximab)
d. a lipid soluble drug
e. a weak base in the acidic stomach environment
Ans: answer: D. A lipid soluble drug
Bioavailability= drug quantity that reaches the target organ. This term takes into account
the amount of drug absorbed in the gut and how much is metabolized by the liver when
the drug passes through it.
Most drugs are absorbed through the gut membranes by passive diffusion across the
lipid bilayer. The ease in crossing the lipid barrier depends on Fick's law: Cout-
Cin=(surface area X permeability coefficient)/Thickness. Lipid soluble drugs have a high
permeability coefficient.
Drugs that are weak basis can be absorbed but are limited by the pH. For example, the
weak base formula shows B + H+ = BH+. Therefore, in the acidic environment of the gut
(increased hydrogen ion content) the reaction will be shifted to the right (Le Chatelier's
principle--TF) or the charged lipophobic state.
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