Pharmacokinetics Flashcards
What does ‘half-life’ mean?
The half-life of a drug is the time it takes for one-half of the drug
to be eliminated from the body.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 42.
What is ‘clearance’?
Clearance refers to the ability of the body to eliminate a drug.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 11th ed. New York: McGraw-Hill; 2009: 37.
What is volume of distribution?
The volume of distribution is a number that describes the
amount of drug in the body compared to how much is actually in
the bloodstream. It is calculated as Vd = Amount of drug in
body/Plasma concentation of the drug. It actually describes an
apparent volume. If a large amount of a drug has been
administered and only a small amount of the drug appears in
the plasma, the drug is said to have a large volume of
distribution.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 38.
What does the term bioavailability mean?
Bioavailability refers to the amount of the drug that is able to
reach its target receptor after it is introduced into the circulatory
system.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 66.
What does the term ‘steady-state’ mean?
Steady-state refers to a state in which all of the tissues in the
body have had time to reach equilibrium. The concentration of
drug differs between organs, but no longer varies from momentto-
moment.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 70.
What pharmacokinetic measurement predicts the
time it takes for half of a drug to be eliminated when
a continuous infusion of the drug is discontinued?
The context-sensitive half-time. It should be noted that context
sensitive half-times are computer models that only predict the
time for 50% of the drug in the central compartment to be
eliminated. It does not predict the time for recovery from the
drug.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 72-73.
What does ‘extent of absorption’ mean?
Extent of absorption refers to the degree a drug reaches the
blood stream from the site of administration. For example, only
about 70% of a dose of digoxin reaches the bloodstream when
it is administered orally.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 43.
How does molecule size affect a drugs ability to
cross a biologic membrane?
The smaller the molecule is, the easier it is for it to cross a
biologic membrane. Usually, molecules heavier than 100-200
Daltons do not cross cell membranes.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 5944.
To what does the term ‘stereochemistry refer?
It refers to the ability for a chemical to have more than one
possible structural arrangement. It is based on the presence of
a structural component called a chiral carbon. The chiral
carbon acts as a point in which a portion of the chemical can be
rotated into another position. The two chemicals are isomers of
each other and often have substantial differences in their
pharmacologic effect.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 69.
How do albumin, alpha-1 acid glycoprotein, and betaglobulin
differ in their ability to bind with drugs?
Although albumin is able to bind to drugs that are acidic,
neutral, or basic, it binds more readily to acidic compounds.
Alpha-1 acid glycoprotein and beta-globulin bind more readily to
basic compounds.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 64.
What factors affect the extent of absorption of a
drug?
Factors that affect the ability of the drug to cross from the GI
tract to the bloodstream affect the extent of absorption (e.g. the
drug is too hydrophilic or too lipophilic, transport mechanisms
may tend to pump the drug back into the gastrointestinal
system, etc).
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 43.
What is the most prevalent protein in the
bloodstream?
Albumin
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 64.
How does protein binding affect the ability of a drug
to exert its pharmacologic effects?
The more protein bound a drug is, the less of the drug is
available to exert its effects and vice versa.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 64.
What is a reversible antagonist?
A reversible antagonist will compete with the agonist for
receptor binding locations and will decrease the ability of the
agonist to activate the receptor. If the relative concentration of
the agonist increases, it can ‘dislodge’ the antagonist from the
receptor and the pharmacologic effects of the antagonist will
diminish.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 18-19.
How is receptor affinity for a drug related to the
potency of a drug?
The lower the affinity of a receptor for a certain drug, the greater
the concentration of the drug must be present to form a
significant number of drug-receptor complexes. In other words,
the lower the affinity, the more of the drug you have to
administer to achieve a certain effect. Potency relates the
amount of a drug that must be administered to achieve its
clinical effect.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 15.
What does the term receptor affinity mean?
Receptor affinity refers to the degree of attraction that exists
between a drug and the receptor to which it attaches. Drugs
with a high affinity for a receptor bind to it easily. Drugs with a
low affinity for a receptor do not tend to bind with it as quickly.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 15.
How do ionized and nonionized forms of a drug
compare in their ability to cross cell membranes?
Ionized forms of a drug are charged and are water-soluble.
Nonionized forms of a drug do not have an electrical charge
and are lipid-soluble. Because cell membranes are composed
of lipids, only lipid-soluble drugs can pass through them easily.
Lipid membranes tend to repel ionized drugs because of their
electrical charge.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 62.
What is the general chemical composition of most
drugs?
Most are salts of either a weak base or a weak acid.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 62
How does hypoalbuminemia affect the action of a
highly protein-bound drug like warfarin?
About 98% of warfarin is protein-bound. As the plasma protein
level decreases, there is less of the protein available for the
drug to bind with, and more of the free form of the drug is
available to exert its pharmacologic action. In summary,
hypoalbuminemia intensifies the action of highly protein-bound
drugs.
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 64-65.
What percentage of the body weight does plasma
constitute?
5%
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 70.
What does the term ‘maximum effect’ mean?
All drugs have a maximum effect. This represents the
maximum response that can be clinically seen. Once this point
is reached, the administration of more of the drug will not
increase the response any further.
Katzung BG, Masters, SB, & Trevor AJ. Basic and Clinical
Pharmacology. 12th ed. New York: McGraw-Hill; 2012: 48.
What percentage of the body weight does adipose
tissue constitute?
20%
Nagelhout JJ, Plaus KL. Nurse Anesthesia. 5th ed. St. Louis,
MO: Elsevier Saunders Company; 2014: 70.
