adams chapter 52013

5/26/2018 Adams Chapter 52013

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PHARMACOLOGYCONNECTIONS TO NURSING PRACTICE

Second Edition

Pharmacology: Connections to Nursing Practice, Second Edition

Michael Patrick Adams Carol Quam Urban

CHAPTER

Pharmacodynamics5


2/24Pharmacology: Connections to Nursing Practice, Second Edition


Pharmacodynamics

Pharmaco= medicines

Dynamics= change

What the drug does to the body

Involves drug mechanism of action

Involves effect of drug concentration onbody responses


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Interpatient Variability

Individuals have different responses todrugs

Responses are related to:

Doseresponse relationships

Therapeutic index

Drug receptor interactions


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Clinical Implications ofInterpatient Variability

Average dose predicts therapeuticresponse in 50%

Client may need less or more of a drug

Need to monitor drug effect on client

Dosage adjustment may be indicated


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Therapeutic Index

Identifies safety index of drugs A common drug with a narrow therapeutic index

= Lanoxin dose range is 0.125 0.250 mg

A common drug with a wide therapuetic range is

metoprolol 12.5 mg 100 mg Median lethal dose (LD50)

Lethal to 50% of test subjects

Effective dose (ED50)

Desired drug response in 50% of subjects


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Median Toxicity Dose

Produces toxicity in 50% of subjects

Extrapolated from clinical trials

Provides practical clinical information


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5.3 The doseresponse relationshipdescribes how the actions of a drug

change with increasing dose.

DoseResponse Relationship


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Drug dose correlates to degree ofresponse

Three phases

Phase 1: lowest phase

Phase 2: most desirable range

Phase 3: plateau reached


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Graded dose-responsive curve

Smooth and continuous

Adjust dose changes in smallincrements

Plateau of phase 3

Increasing dose will not increase

therapeutic effect

Increasing dose could cause toxicity

Reaches a ceiling


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Figure 5.3 Dose-response relationship.


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5.4 Potency and efficacy arefundamental concepts of

pharmacodynamics that describe adrugs activity.

Potency and Efficacy


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Figure 5.4 Potency and efficacy: (a) Drug A has a higher potency than drug B. (b) Drug A has a higher efficacythan drug B.


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Potency and Efficacy

Not all drugs have equal efficacy

Drugs in same class can differ inpotency and efficacy

Potency compares doses of twodifferent drugs

Most common application is

equianalgesic dose chart


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Figure 5.4 (continued) Potency and efficacy: (a) Drug A has a higher potency than drug B. (b) Drug A has ahigher efficacy than drug B.


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Efficacy

Greatest maximal response producedby drug

Compares desired therapeutic effect of

two drugs


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5.5 Most drugs produce their actionsby activating or inhibiting specific

cellular receptors.

Receptor Theory


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Receptor Theory

Most drugs enhance or inhibit aphysiological process

Medications bind to receptors

Drug receptor binding is like lock andkey

Once occupied, receptor triggers

second messengerBiochemical events occur

Drug stimulates or inhibits activity


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Figure 5.5 Types of cellular receptors: (a) Drug binds to the receptor opening channel. (b) Drug binds to thereceptor, causing a G proteinmediated reaction in the cell. (c) Drug binds to the transmembrane receptor tosignal a change inside the cell. (d) Drug enters the cell nucleus to increase synthesis of specific proteins.


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5.6 Agonists, partial agonists, andantagonists compete for cellular

receptors and can modify drug action.

Agonists and Antagonists


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Agonists

Mimic the action of endogenoussubstances

Response may be greater than

endogenous activity

Opioid agonists

Partial agonists

Produce weaker action than endogenoussubstances


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Antagonists

Prevent action of endogenoussubstances

May compete with agonists

Useful in blocking excess endogenousactivity

May reverse adverse effects of

overdoses Most common is an opioid antagonist

Narcan (naloxone)


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Figure 5.6 Agonists, partial agonists, and antagonists: (a) An agonist results in maximum response. (b) Apartial agonist results in less than maximum response. (c) An antagonist results in little or no response. (d) Anagonist plus antagonist results in diminished response.


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5.7 In the future, pharmacogeneticsmay allow customization of drug

therapy.

Pharmacogenetics


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h l k d C l Q b

Pharmacogenetics

Drug therapy not effective for everyone

Human genome project

Genetic differences in drug-metabolizing enzymes

adams chapter 52013

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