11: Pharmacology


As a health care provider responsible for client assessment and care, the dental hygienist must understand drugs, the conditions for which these drugs are used, and the actions, range of effects, and interactions of the drugs. The health, dental, and pharmacologic histories are the foundation on which decisions regarding client care rest. For example, some clients may need prophylactic antibiotic premedication before dental and dental hygiene care. Therefore, before care is planned, the client’s medical conditions and the medications used to manage them are assessed and recorded in the client’s permanent record. Contraindications or cautions to professional care concerning these drugs are determined using appropriate references and consultations. Through this knowledge, medical emergencies may be prevented; and, if an emergency occurs, the oral health care team can act within the standard of care.

General Considerations


Pharmacology—the study of drugs and their effects on living organisms

Pharmacotherapy—the use of medications to treat different disease states

Pharmacodynamics—the action of drugs on living organisms

Pharmacokinetics—what the body does in response to the drugs (e.g., absorption, distribution, metabolism, excretion)

Pharmacy—the practice of compounding, preparing, and dispensing drugs and of counseling clients about their medications

Toxicology—the study of the harmful effects of drugs on living organisms

1. Drugs—biologically active substances that can modify cellular function; used in the prevention, diagnosis, treatment, and cure of disease or in the prevention of pregnancy

2. Nomenclature—each drug has several names

Table 11-1 lists the Latin abbreviations used in prescription writing

TABLE 11-1

Common Latin Abbreviations Used in Prescription Writing

Abbreviation Interpretation
a., ante Before
a.c., ante cibum Before meals
A.D., auris dextra Right ear
A.L., auris laeva Left ear
b.i.d., bis in die Twice per day or twice daily
gt., gutta Drop (plural gtt.)
h., hora Hour
h.s., hora somni At bedtime
o.d., oculus dexter Right eye
o.s., oculus sinister Left eye
o.u., oculus uterque Each eye
p.c., post cibum After meals
p.o., per os By mouth
p.r. By rectum
p.r.n., pro re nata As needed
q.d., quaque die Once per day or once daily
q.i.d., quater in die Four times per day
q.o.d. Every other day
q.h. Every 6 hours
sl. Sublingual
supp. Suppository
t.i.d., ter in die Three times per day
u.d. As directed



1. Physicians’ Desk Reference (PDR)1—provides an index of drug manufacturers, brand and generic names of drugs, product categories, drug identification and information guide, and diagnostic information; updated yearly; most commonly used reference in the oral health care environment; inclusion of a drug in this reference is paid for by the manufacturer (seldom-used products not listed); information about the drug is similar to that found in the package insert, but this information is not updated regularly

2. Facts and Comparisons2—drugs organized by pharmacologic classes; complete listing; updated monthly; contains both prescription and over-the-counter (OTC) drugs; prepared by independent editors

3. Applied Pharmacology for the Dental Hygienist;3 Oral Pharmacology for the Dental Hygienist;4 Basic Principles of Pharmacology with Dental Hygiene Applications5—basic pharmacology textbooks for the dental hygienist; all three focus on dental hygiene considerations and provide the necessary information to avoid adverse reactions and drug interactions

4. Mosby’s Dental Drug Reference6—provides comments on a limited number of drugs specifically related to dentistry; includes dental drug interactions, oral side effects, and dental considerations

5. Drug Information Handbook for Dentistry7—provides an alphabetical listing of drugs and their effects on dental therapy; sections on managing medically compromised clients and treating specific oral conditions; information on dental office emergencies; comprehensive appendix on dental drug interactions and OTC dental products

6. Drug Information for the Health Care Professional, Volume 1, and Advice for the Patient, Volume 2;8 published yearly and updated quarterly by U.S. Pharmacopoeia; includes basic information regarding pharmacology, pharmacokinetics, adverse reactions, drug interactions, doses, and advice to the patient

CD-ROM sources—more titles are becoming available; it is important to preview CD-ROMs before purchasing them because the ease of computer access (“user-friendliness”) varies considerably; many can be purchased with quarterly updates included

Internet sites—extensive and growing volume of information; use a search engine to explore sites related to dental hygiene (see the table titled “Web Site Information and Resources” at the end of this chapter)

Drug Action

Log dose–response curve—as the dose of a drug increases (x axis), the percentage of maximum response increases (y axis) until increasing the dose further produces no increase in the percentage of response (the effect of the drug reaches a plateau) (Figure 11-1)


1. Effective dose (ED) 50—dose that produces 50% of the maximum response, or the dose of a drug that produces a specific response in 50% of the subjects

2. Lethal dose (LD) 50—dose that is lethal to (kills) 50% of the subjects; laboratory animals are used to derive LD

3. Therapeutic index (TI)—LD50 divided by ED50; a measure of the safety of a drug

4. Onset—time required for a drug’s effect to begin; onset is short if the drug is given intravenously, longer if administered orally

5. Duration—length of time a drug’s effect lasts; related to a drug’s half-life

6. Half-life (image)—time required for a drug’s serum concentration to decrease by 50%; five half-lives are required for a drug to be eliminated from the body

7. Potency—amount of drug (e.g., in milligrams) needed to produce an effect; the more potent an agent is, the lower is the dose needed to produce an effect (Figure 11-2)

8. Efficacy—the desired effect elicited by a drug, independent of dose (see Figure 11-2)

9. Tolerance—physiological response to the same dose produces less effect, or a higher dose is required to achieve the same effect

10. Therapeutic effect—desired pharmacologic effect

Routes of administration

1. Oral (PO)—by mouth; easiest to use; good client acceptance; however, a latency period exists

2. Rectal—administration by suppository or enema; produces either local or systemic effect

3. Parenteral—a route other than an oral route; usually refers to an injection

4. Intravenous (IV)—administration into a vein; shortest onset of action and higher risk of adverse events compared to other routes of administration

5. Intramuscular (IM)—administration into the muscle; sometimes painful

6. Subcutaneous (SC, SQ)—injected beneath the skin (e.g., insulin)

7. Intradermal—injected into the dermis (e.g., skin test for tuberculosis produces a bleb [bump]; progesterone implants are administered intradermally)

8. Intrathecal—administered into the spinal fluid (e.g., to treat meningitis)

9. Intraperitoneal—injected into the peritoneal cavity (abdomen)

10. Oral or nasal—particles, volatile liquids, or gasses that are inhaled (e.g., nitrous oxide–oxygen (N2OimageO2) analgesia; as are some medications used to treat allergies and asthma)

11. Topical—ointments or creams applied to the skin or mucous membranes (e.g., hydrocortisone)

12. Sublingual—a tablet that dissolves or a solution that is sprayed under the tongue (for systemic effect)

Dosage forms


Adverse Reactions

Side Effect

Side effect on a nontarget organ—effect on an organ other than that intended to be altered (e.g., insomnia resulting from a β2-agonist or theophylline); dose-related and often predictable

Toxic reaction—predictable and dose-related effect on a target organ (e.g., insulin can lower blood glucose levels to the point of hypoglycemia)

Allergic reaction—varies from mild rash to anaphylaxis; involves an antigen–antibody reaction (e.g., rash from penicillin); can include urticaria, soft tissue swelling, and difficulty breathing; not predictable and not dose related

Idiosyncrasy—abnormal drug response that is genetically related

Interference with natural defense mechanisms—body is less able to fight infection (e.g., steroids weaken the immune system)

Teratogenic effect—adverse effect on a fetus (e.g., alcohol intake during pregnancy produces fetal alcohol syndrome)

Safety—related to the therapeutic index; therapeutic index: LD50/ED50. The measure of a drug’s safety can be determined using this formula; the larger the number of this ratio, the safer is the drug


Pharmacokinetics is the way in which the body responds to drugs through the four processes of absorption, distribution, metabolism, and excretion (ADME)

Absorption depends on:

Distribution of the drug (Figure 11-3)9

1. Drugs are transported to the site of action

2. Only the free, or unbound, drug can cross cell membranes (indicated by arrows between boxes in Figure 11-3)

3. In each cellular compartment, equilibrium is reached between the bound and unbound (free) drug

4. Redistribution—the drug moves from one tissue (where it exerts an effect) to another tissue (where it is inactive); this is one method of terminating a drug’s effect

5. Protein binding—drugs bind to protein receptors to varying degrees; once the drug binds to a protein receptor, it cannot exert its pharmacologic effect; when more than one drug is present in the system, the drugs may compete for the same receptor site; the drug with the stronger affinity will bind to the receptor site, and the drug with the weaker affinity will then exert its pharmacologic effect

6. Tissue binding—some drugs can also bind to body tissues and cause significant chemical effects (e.g., tetracycline has an impact on developing bones and teeth of the fetus and of a young child)

Metabolism (biotransformation)—takes place mainly in the liver by hepatic microsomal enzymes; metabolites are more polar, less protein bound, and more easily excreted; drugs metabolized by microsomal enzymes can affect their own metabolism or that of other drugs (e.g., either increasing [as with barbiturates] or decreasing [as with cimetidine, erythromycin] the rate of metabolism); biotransformation is a source of drug interactions

Excretion—usually by way of kidneys (urine); can also occur through feces (enterohepatic circulation), sweat, tears, or lungs (e.g., N2O is exhaled)

Autonomic Nervous System Agents

Agents affecting the autonomic nervous system are divided into four groups: parasympathetic (P) nervous system stimulation (P+) and inhibition (P−), and sympathetic (S) nervous system stimulation (S+) and inhibition (S−).

Sympathetic (Adrenergic) Agents

Mimic the action of the sympathetic autonomic nervous system (SANS); act like norepinephrine (NE) in the SANS, producing stimulation of the SANS; epinephrine produces the same effect (Figure 11-4)

Adrenergic agonists

Pharmacologic effects and adverse reactions

1. The central nervous system (CNS)—stimulation produces increased alertness; may also cause anxiety, anorexia

2. Stimulation of the heart—S+, produces

3. Vascular effects (on the arterial tree) result from

4. Mydriasis (pupil dilation) and reduced intraocular pressure; useful in treating glaucoma

5. Bronchodilation (by action of β2-agonist); useful in treating clients with asthma

6. Alterations in the blood glucose level; persons with diabetes mellitus must be observed for adverse reactions

7. Production of thick, viscous saliva

Drug interactions—examples of interactions caused by adrenergic agents are listed below:

Dental hygiene considerations—the client’s pulse and blood pressure must be checked; all of these medications can increase heart rate and blood pressure

Therapeutic uses (Table 11-3)

TABLE 11-3

Adrenergic Agents and Their Use

Adrenergic Agent Receptor Stimulated Comments
Epinephrine (Adrenalin) αβ Endogenous catecholamine; local anesthetic additive
Methylphenidate (Ritalin) α Attention deficit hyperactivity disorder (ADHD)
Phenylephrine (Neo-Synephrine) α Nasal decongestant
Levonordefrin (Neo-Cobefrin) α > β Local anesthetic additive
Amphetamine αβ Diet pill (abused)
Pseudoephedrine (Sudafed) αβ Orally active nasal decongestant

Adrenergics as vasoconstrictors are contained in local anesthetic solutions

1. Examples

2. Advantages of adrenergic vasoconstriction

3. Disadvantages of adrenergic vasoconstriction

a. Excessive amount produces systemic toxicity

b. In persons with cardiovascular disease:

c. Hyperthyroidism—vasoconstrictors may produce a thyroid storm in clients who have not received treatment and in those receiving drug therapy; thyroid storm or thyroid crisis is characterized by an acceleration of all body processes (e.g., increases in heart rate, blood pressure, respiration, body temperature, and pulse); pulmonary edema and congestive heart failure can occur

4. Minimize toxicity by:

5. Dental hygiene considerations

β-Adrenergic Blocker (β-Blocker) Antagonists

See the section on “Cardiovascular Agents” for more information.

Mechanism of action—drug blocks SANS action (β-receptors); some β-blockers are more selective for the β1-receptor than β2-receptor; some drugs are formulated to target β1-receptors, others to β2-receptors; other drugs target both β1 and β2 receptors

Used to treat hypertension, angina, arrhythmias; also congestive heart failure, anxiety, and glaucoma; and used to prevent myocardial infarction (MI, heart attack)

Examples (note generic names ending with “olol”)

Dental hygiene considerations

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Jan 1, 2015 | Posted by in Dental Hygiene | Comments Off on 11: Pharmacology

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