Pharmacodynamics is the study of how drugs act on the body and examines the biochemical and physiologic effects of drugs. It focuses on the drug's effects on cells and tissues. There are three main ways drugs can exert their effects: receptor interactions, enzyme interactions, and nonspecific interactions. The goal of drug therapy is to produce a therapeutic effect, while minimizing adverse effects. Drug response is monitored to evaluate therapeutic effects and detect undesirable side effects or toxicity.

1. PHARMACODYNAMICS
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2. Pharmacologic Principles
Pharmacodynamics
• the study of drug concentration and its effect in the body.
– WHAT THE DRUG DOES TO THE BODY
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3. Pharmacodynamics
A positive change in a physiologic system is called a
THERAPEUTIC EFFECT
This is the goal of drug therapy
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4. DRUG RESPONSE CAN CAUSE:
• PRIMARY EFFECT
– the desirable effect; the immediate and first action of the
drug producing one group of symptoms.
• SECONDARY EFFECT
– maybe desirable or undesirable;
– not primarily a drug effect and can be cause mainly by the
organism’s reaction to the primary effect/action.
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5. Pharmacodynamics
Drugs exert their action on cells in 3 ways:
a) Receptor interactions
b) Enzyme interactions
c) Nonspecific interactions
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6. Pharmacodynamics
a) Receptor interactions
• Key in a lock
• Drug binds to a specific site on the cell
(called a receptor site) and modifies the
function of the cell
• How many drugs work
• How strong a drug binds to the receptor
site is called the AFFINITY for that
binding site
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7. Pharmacodynamics
a) Receptor interactions
• AGONISTS
 Drugs that fit well at the receptor
site and elicit desired
action/function of the cell
 Mimics the substance that
activates them
• ANTAGONISTS
 Drugs that attach to the receptor
site and block other drugs from
attaching
 Blockers of receptor sites
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8. Pharmacodynamics
a) Receptor interactions
• Both Agonists and Antagonists are used in drug
therapy
– Albuterol inhaler- for asthma is an example of an agonist medicine
– Benadryl ( diphenhydramine) is an antagonist.
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9. Pharmacodynamics
b) Enzyme interactions
– The drug alters the enzymes necessary for a
certain body function
The Ace Inhibitor class of blood pressure medicines are an example of
drugs that exert their action by altering enzyme pathways
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10. Pharmacodynamics
c) Non-specific interactions
–alter the cell structure
–alter some crucial cell process
Antibiotics are an example of drugs that alter the cell wall or
alter the internal function of the bacterial cell
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11. Pharmacodynamics
 Once the drug is at the site of action, it can modify the
rate (increase or decrease) at which the cells or tissues
function
 A drug cannot make a cell or tissue perform a function it
was not designed to perform
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12. Pharmacodynamics
CATEGORIES OF DRUG ACTION
1. STIMULATION OR DEPRESSION of cell activity
• Stimulation= increases the rate of cell activity or the secretion from a gland;
• Depression=cell activity and function of a specific organ are reduced.
2. REPLACEMENT
• drugs that replace essential body compounds (e.g., insulin)
3. INHIBITION OR KILLING OF ORGANISMS
• drugs that interfere bacterial cell growth.
4. IRRITATION
• drugs that act as irritants to increase specific organ functions (e.g., laxative)
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13. OTHER (TOXIC) EFFECTS OF DRUGS IN THE
BODY
1.SIDE EFFECTS
– physiologic effects not related to the desired drug effects;
– even with a correct drug dosage, side effects occur and are predicted.
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14. OTHER (TOXIC) EFFECTS OF DRUGS IN THE BODY
2. ADVERSE EFFECTS
– more severe than slide effects;
– unpleasant or even dangerous
– can occur for a number of reasons:
1. The drug may have other effects on the body besides the therapeutic effect.
2. The client is sensitive to the drug being given.
3. The drug’s action in the body causes other responses that are undesirable or
unpleasant.
4. The client is taking too much or too little of the drug, leading to adverse
effects.
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15. OTHER (TOXIC) EFFECTS OF DRUGS IN THE
BODY
HYPERSENSIVITY
– excessive responsiveness to either the primary or
secondary effects of a drug;
– may result from a pathologic or underlying
condition.
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16. DRUG ALLERGY
• causing an immune response when the person is exposed to the
drug
Types:
1. ANAPHYLACTIC REACTION
– Antibody reacts with specific site in the body to cause the release of
chemical.
2. CYTOTOXIC REACTION
– antibodies that circulates in the blood and attacks antigen (the drug)
on cell cite causing death of that cell;
– reaction is not seen immediately.
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17. DRUG ALLERGY
Types:
3. SERUM SICKNESS REACTON
– Antibodies circulates in the blood and cause damage to various
tissues by depositing in blood vessels
– may occur after a week or more after the exposure to the drugs.
4. DELAYED ALLERGIC REACTION
– occurs several hours after exposure and involves antibodies that
are bound to specific WBC.
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18. DRUG INDUCED TISSUES AND ORGAN DAMAGE
1. DERMATOLOGIC REACTION
– adverse reaction in skin such as rashes, hives
– many drugs can be deposit in the skin or cause direct irritation
to the tissue.
2. SUPER INFECTION
– several drugs like antibiotics, destroy the normal flora leading
to the development of infection caused by the usually
controlled organisms in the body.
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19. DRUG INDUCED TISSUES AND ORGAN DAMAGE
3. BLOOD DYSCRASIA
– bone marrow suppression caused by drug effects;
– occurs when drug that can caused cell death are used
causing the rapidly multiplying bone marrow cells to die.
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20. DRUG INDUCED TISSUES AND ORGAN DAMAGE
4. TOXICITY
1. OTOTOXICITY
• damage to the cochlear and vestibular nerves causing deafness.
2. HEPATOTOXICITY
• damage to the liver manifested by an increased in liver enzyme and failure of the liver to function.
3. NEPHROTOXICITY
– damage to the nephrons of the kidney causing kidney failure.
4. CNS DEPRESSION
– vital center of the body found in the central nervous system such as respiratory center is
depressed manifested as changes in the rate and depth of breathing.
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21. End
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22. Pharmacologic Principles
1) Pharmaceutics
2) Pharmacokinetics
3) Pharmacodynamics
4) Pharmacotherapeutics
5) Pharmacognosy
6) Toxicology
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23. Pharmacologic Principles
4) Pharmacotherapeutics
The use of drugs and the clinical indications for
drugs to prevent and treat diseases
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24. Pharmacotherapeutics
 Acute therapy-------- stroke, heart attack
 Maintenance therapy--- hypertension, hyperlipidemia,
 Supplemental/replacement therapy----insulin, iron, thyroid
 Palliative therapy--- high dose opioids for cancer patients,
 Supportive therapy—fluid and electrolytes, volume expanders
 Prophylactic therapy--- antibibiotics before surgery
 Empiric therapy– experience shows it works- no evidence-
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25. Pharmacotherapeutics
Therapeutic Drug Monitoring
• Certain drugs need close monitoring of blood levels during
administration
• They have a potential to become toxic--
some can become toxic at very low blood levels
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26. Pharmacotherapeutics
Therapeutic Drug Monitoring
• The goal is to have enough drug in the body to get the positive
desired effect--without producing undesirable adverse effects or
toxicity. If the peak is too high, organ damage may result. If the
trough is too low, the drug may not be at therapeutic levels
• Some drugs have a very narrow range between therapeutic and
toxic
• Digoxin (heart med) and Gentamycin (antibiotic) are
examples of drugs commonly monitored with blood levels
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27. Pharmacotherapeutics
Therapeutic Drug Monitoring
Peak Level
• Highest blood level
Trough Level
• Lowest blood level
• Blood is drawn at specfic times before and after drug
administration--- the amount of the drug in the body guides the
pharmacist in adjustment of drug dosages
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28. Pharmacotherapeutics
Monitoring
 The effectiveness of drug therapy must be evaluated
– Intended therapeutic action (beneficial)
– Unintended but potential adverse effects (predictable,
adverse reactions)
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29. Pharmacotherapeutics
Monitoring
• Therapeutic index
• Drug concentration
• Patient’s condition
• Tolerance and dependence
• Interactions
• Adverse drug effects
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30. Pharmacotherapeutics
MONITORING
 Therapeutic index
 Ratio of safety: the range between a drug’s therapeutic & toxic effects– a
LOW therapeutic index means the drug has a greater chance of causing an
adverse reaction
 Drug concentration
 Drug levels may become toxic if increased i.e.: renal/hepatic patients whose
normal mechanisms for metabolism and excretion are compromised
 Patient’s condition
 Diseases and and other conditions such as stress and anxiety are just a few
examples of conditons that can alter a patient’s response to drug therapy
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31. Pharmacotherapeutics
MONITORING
 Tolerance
 a decreasing response to repeated doses
 Dependence
 a physiological or psychological need for a drug
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32. Pharmacotherapeutics
Monitoring
• Interactions
The alteration of the action of a drug by other substances
 may occur with other drugs or food
 Other prescribed drugs
 Over-the-counter medications-
 Herbal therapies
 Certain foods
Important to get a good nursing history of all drugs, herbs and
problem foods that patient is taking
Older patients are typically on multiple medications that may
interact--- “polypharmacy”
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33. Pharmacotherapeutics
Monitoring
• Interactions
Drug interaction issues
– Additive effect--smaller doses can be given with same effect ie.
Tylenol and Codeine
– Synergistic effect—2 drugs have a greater effect than either drug
alone-- HCTZ with enalapril
– Antagonistic effect--2 drugs have less of an effect than with
either drug alone-- antacids with tetracycline-
– Incompatibility—2 drugs mixed together and one or more
deteriorates---furosemide and heparin
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34. Pharmacotherapeutics
Monitoring
Interactions
• Incompatibility- can be oral or IV drugs
Focus for nurses when giving different IV drugs together
Drugs may precipitate, become hazy, or change color when
they are incompatible in the same IV tubing
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35. Pharmacotherapeutics
Monitoring
Adverse Drug Events
 Potential hazards of medication use
can be mild and minor
can be life- threatening
 Two broad categories
1. Medication errors
2. Adverse drug reactions
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36. Pharmacotherapeutics
Monitoring
Adverse Drug Events
1. Medication errors
Big focus in all health care areas today
Can occur anywhere along the chain-
prescriber, pharmacist, nurse, technician
Medication errors are PREVENTABLE
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37. Pharmacotherapeutics
Adverse drug reactions
Any reaction to a drug that is unexpected and undesirable that occurs at
therapeutic doses
1. Hypersensitivity (allergic) reaction
2. Pharmacologic reactions
Predictable, well-known reactions that result in little or no change in
patient management
-Predictable frequency
Usually resolve when the drug is discontinued
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38. Pharmacotherapeutics
Contraindications to therapy
• Any characteristic of the patient, especially a disease
state, that makes the use of a given medication
dangerous for the patient
• It is important to assess for contraindications!
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39. Pharmacotherapeutics
Contraindications to therapy
• When the drug will be dangerous for the pt.
 Allergic to drug
 Pregnant
 Impaired liver or kidney function
 Wrong drug for the problem
 Many others
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40. Pharmacologic Principles
5) Pharmacognosy
The study of natural (plant and animal) drug
sources
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41. Pharmacologic Principles
5) Pharmacognosy
• Four main sources for drugs
1. Plants
2. Animals
3. Minerals
4. Laboratory synthesis
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42. Pharmacologic Principles
5) Pharmacognosy
• The source of all early drugs was from nature
– Foxglove--cardiac drugs
– Insulin– pigs and beef
– aluminum hydroxide
• Most new drugs are created synthetically in the lab
– can be mass produced
• We continue to discover many natural sources for drugs
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43. Pharmacologic Principles
6) Toxicology
• The study of poisons and unwanted responses to drugs
and other chemicals
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44. Toxicology
Drug Related Effects
 Teratogenic
drugs or chemicals that result fetal defects
Accutane
 Mutagenic
drugs or chemicals that cause permanent changes in the genetic
composition
may pose a genotoxic hazard to hospital personnel or family
members caring for the patient.
 Carcinogenic
drugs, chemicals etc. that cause cancer
Tobacco
Tamoxifen
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45. Toxicology
• http://toxicology.ucsd.edu/modules.htm
California Teratogen Information Service & Clinical Research Program
(800) 532-3749 (CA only),
UCSD Medical Center , Department of Pediatrics
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