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2
Fundamentals of Drug
Action
EDUCATIONAL OBJECTIVES
After reading this chapter, the reader should be able to:
1. Describe common routes of drug administration.
2. Identify the various types of pharmaceutical preparations.
3. Compare the differences between pharmacodynamics and pharmacokinetics.
4. Describe the characteristics of drug molecules.
5. Describe the mechanisms of drug absorption through the various membranes in the body.
6. Describe absorption through the different routes of drug administration.
7. Describe the drug–receptor interaction.
8. Distinguish between a loading dose and a maintenance dose.
9. Describe the various factors involved in the biological variations of drug dosing.
LECTURE OUTLINE
I. Drug Administration
A. Pharmaceutical preparations.
1. Dosage forms.
a. Liquid.
b. Solid.
B. Routes of drug administration.
1. Enteral.
2. Parenteral.
a. Intravenous (IV)
b. Intramuscular (IM)
c. Subcutaneous (SQ)
3. Topical.
a. Epicutaneous.
b. Subgingival.
c. Inhalation.
d. Optic.
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e. Otic.
II. Pharmacokinetics
A. Definition.
B. Crosses many membranes to reach target cells/organs.
C. Categories.
1. Absorption.
2. Distribution.
3. Metabolism (biotransformation).
4. Elimination.
D. Passage of Drugs through plasma membranes.
1. Passive transport.
2. Active transport.
E. Absorption of drugs.
1. Definition.
2. Bioavailability.
3. Factors affecting absorption of drugs into the blood.
a. Route of administration of drug.
b. Drug dosage.
c. Digestive motility.
d. Drugdrug, drugfood, drugherbal interactions.
e. Blood flow at site of administration.
f. Degree of ionization of drug.
g. pH of local environment.
F. Distribution of drugs.
1. Definition.
2. Factors affecting distribution.
a. Amount of blood flow to tissues.
b. Fatty tissue’s ability to accumulate and store drug.
c. Drugprotein complexes; protein binding.
d. Bloodbrain barrier.
G. Metabolism (biotransformation) of drugs.
1. Definition.
2. Liver as primary site.
3. Biochemical reactions.
a. Hydrolysis.
b. Oxidation.
c. Reduction.
d. Addition of conjugate.
4. Hepatic (liver)microsomal enzyme system.
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a. P450 isoenzymes: Cytochrome (CYP).
5. Prodrugs.
6. First-pass effect.
a. Oral drugs.
b. Drugs changed to inactive form.
H. Elimination of drugs.
1. Elimination versus excretion of drugs, definitions.
2. Kidneys.
a. Primary site of excretion.
b. Filtration.
c. Reabsorption.
d. Secretion.
e. Excretion.
3. Other sites of elimination.
a. Respiratory system.
b. Glands.
c. Biliary system; enterohepatic recirculation.
I. Kinetics of elimination.
a. First-order kinetics.
b. Zero-order kinetics.
c. Half-life.
d. Steady-state plasma concentration.
J. Drug dosing.
a. Drug dose.
b. Drug action.
c. Loading dose.
d. Maintenance dose.
K. Therapeutic drug responses.
a. Minimum effective concentration.
b. Toxic concentration.
c. Therapeutic range (margin of safety).
III. Pharmacodynamics
A. Definition.
B. Clinical applications.
1. Drug actions.
a. Drugreceptor interactions.
i. Drug binds to receptor—lock-and-key theory.
ii. Receptors.
(a) Proteins.
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(b) Cellular plasma membrane.
(c) Ionic bonds most common mechanism for drug binding.
iii. Ligand.
iv. Affinity.
v. Efficacy.
vi. Potency
vii. Ceiling effect
b. Competition for receptors: Drugdrug interactions.
i. Agonist.
(a) Definition.
(b) Function.
ii. Partial agonist.
iii. Antagonist.
(a) Definition.
(b) Function.
iv. Agonistantagonist relationships.
C. Doseresponse relationships.
1. Maximal response.
2. Log dose.
3. Doseresponse curve.
4. Biophase: The higher the dose, the greater the effect seen.
5. Potency: ED50.
6. Efficacy.
J. Therapeutic index and drug safety.
1. Median effective dose (ED50).
2. Median lethal dose (LD50).
3. Therapeutic index.
a. Drug safety.
b. Higher the value, the safer the drug.
4. Median toxicity dose (TD50).
K.
Drug Effects
1. Adverse drug reactions (ADR)
2. Adverse drug events (ADE)
3. Toxicity
4. Idiosyncracy
5. Allergic response
6. Mutagenic effect
7. Tetratogenic effect
K. Factors that modify the effects of drugs.
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1. Biological variation.
2. Adaptation.
3. Tolerance.
4. Tachyphylaxis.
L. Placebo response.
1. Placebo.
2. Clinical trials.
TEACHING TIPS
1. Have students explain the various routes of drug administration and specify
which are used in dentistry.
2.
Introduce the students to using information obtained
from
the
Internet.
For
example,
have
students
visit
www.merck.com/mmhe/sec02/ch012/ch012c.html. Look at the dynamics of drug
action. Have the students discuss their findings. (This site is great for
pharmacology information.)
3. Explain the importance of how drugs work. Students should know the impact of
these “ABCs” in the overall learning and understanding of how drugs work. This
is important because many drugs are prescribed in the dental office.
4. Have the class explain how dosing for a drug is determined. For example, give
examples of the half-life of antibiotics and how dosing is determined from the
half-life of the drug.
5. Use flash cards for students to learn the features of how a drug binds to a
receptor to facilitate drug action.
6. Using graphs, explain the difference between efficacy and potency of a
medication.
FACTOIDS
1. Most drug absorption occurs in the small intestine. If the small intestine were
flattened out, it would be about 5,400 square yards or about the area of a football
field.
2. If an average man had a metabolism of a hummingbird he would have to eat 285
pounds of hamburger every day to maintain his weight.
DISCUSSION QUESTIONS
1. Discuss the observable consequences of drug action; for example, the action of
penicillin is to interfere with cell wall synthesis of bacteria.
2. Discuss factors affecting drug absorption (e.g., foods, other medications).
3. Discuss the difference between a loading dose and a maintenance dose.
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4. Divide the students into groups of two or three. Assign each group a random
drug. Have each group make cards for each classification of drug names listing
the trade, chemical, and generic names. Discuss the concept of bioequivalence.
5. Discuss in groups the various routes of dental drug administration with examples
of each route.
6. Explain the applications of a drug’s (e.g., antibiotics) plasma half-life (t1/2) to
pharmacotherapy. For example, using the concept of half-life explain why
certain antibiotics are dosed every 8 hours versus every 6 hours.
CLASSROOM ACTIVITIES
1. Have each student make cards for each concept of pharmacokinetics.
2. Have each student make cards for each concept of pharmacodynamics.
3. Give an example of an orally administered drug such as acetaminophen. Have
the student draw a picture and a flow chart showing how acetaminophen goes
through the body, describing the steps: disintegration of tablet, absorption,
distribution, biotransformation, and elimination. Allow class time to share
information with the rest of the class.
4. Have students bring an anonymous sample medical history of a patient and
review the drug names, mechanism of action, and elimination of each drug.
5.
Have each student draw a diagram of a drugreceptor complex.
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