Download Drug Slides Ch. 3

How and Why Drugs Work
Chapter 5
Intended and Unintended
Effects of Drugs
Intended responses:
◦ Reason for using the drug
 Unintended responses:
◦ Side effects
 The main distinction between intended
responses and side effects depends on the
therapeutic objective. (what is the purpose of
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taking the drug)
Common Side Effects of Drugs
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Nausea or vomiting
Changes in mental alertness
Dependence
◦ Withdrawal
Allergic reactions
Changes in cardiovascular activity
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Common Side Effects of Drug (continued)
Side Effects of Drugs – Risk, Cost, vs. Benefit
• Are the therapeutic benefits of the drug
greater than the risk of the drug?
• Does the benefit of the drug outweigh
the potential amount of cost the drug
may cause in side effects?
•Is the cost of not taking the medication
greater than the alternative medical
treatment?
Dose-Response
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Many factors can affect the way an
individual responds to a drug, including the
following:
◦ Dose – Amount of the drug taken
◦ Tolerance – Changes in the body that decrease
response to a drug even though the dose remains the
same
◦ Potency – The amount of drug necessary to cause
an effect
Dose-Response (continued)
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Additional factors
◦ Pharmacokinetic properties:
 Rate of absorption
 Manner distributed throughout the body
 Rate metabolized and eliminated
◦ Form of the drug
◦ Manner in which the drug is administered
Dose-Response Curve (see Fig. 5-2, p.151)
Margin of Safety
• The range in dose between the amount of
drug necessary to cause a therapeutic effect
and a toxic effect.
Potency vs. Toxicity
• Potency: The amount of drug necessary to cause
an effect. The smaller the drug amount required to
perform the desired therapy, the greater the
potency.
• Toxicity: The capacity of a drug to do damage
or cause adverse effects in the body. A high
potency drug has a greater capacity for toxicity
Drug Interaction
Additive effects
◦ Summation of effects of drugs taken
concurrently
 Antagonistic (inhibitory) effects
◦ One drug cancels or blocks effects of
another
 Potentiative (synergistic) effects
◦ Effect of a drug is enhanced by another
drug or substance. (synergism)
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Pharmacokinetic Factors
That Influence Drug Effects
 Administration - How does the drug enter the body?
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Absorption – How does the drug move from the site of
administration?
Distribution – How does the drug move to the various
areas in the body?
Activation – How and where does the drug produce its
effects?
Biotransformation and elimination – How is the
drug inactivated, metabolized, and/or excreted from the
body?
Forms and Methods
of Taking Drugs
• Oral ingestion
•Rate and Stomach contents
•Must pass through liver
following digestion
• Inhalation
• Injection
•Intravenous
•Intramuscular
•Subcutaneous
• Topical application
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Forms and Methods of Taking
Drugs
Distribution
Most drugs are distributed throughout the body in the blood.
 It takes approximately one minute for a drug to circulate
throughout the body after it enters the bloodstream.
 Drugs have different patterns of distribution depending on their
chemical properties.

 Their ability to pass through membranes
 Their molecular size
 Their solubility properties
 Their tendency to attach to proteins and tissues throughout the body.
Required Doses for Effects
Threshold dose: The minimum amount of
a drug necessary to have an effect
 Plateau effect: The maximum effect a
drug can have regardless of the dose
 Cumulative effect: The buildup of drug
concentration in the body due to multiple
doses taken within short intervals
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Time-Response Factors
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The closer a drug is placed to the target
area, the faster the onset of action.
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Acute drug response:
◦ Immediate or short-term effects after a single drug dose
Chronic drug response:
◦ Long-term effects after a repeated doses
Cumulative Effects – buildup of a drug in the body
after multiple doses taken at short intervals
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Biotransformation
Biotransformation: The process of
changing the chemical or pharmacological
properties of a drug by metabolism.
 The liver is the major organ that
metabolizes drugs in the body.
 The kidney is the next most important
organ for drug elimination.
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Biotransformation
Physiological Variables That
Modify Drug Effects
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Age
Gender
Pregnancy
Underlying causes in each are
changes that occur in body
composition, physiology, and
organ changes
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Adaptive Processes
Tolerance: Changes causing decreased
response to a set dose of a drug
 Dependence: The physiological and
psychological changes or adaptations that
occur in response to the frequent
administration of a drug
 Withdrawal (see diagram on following slide, Fig 5.4,
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p. 152)
Adaptive Processes (continued)
Tolerance
Reverse tolerance (sensitization): Enhanced
response to a given drug dose; opposite of
tolerance. If sensitized, you would have the same
response to a lower dose of a drug as you initially did to
the original higher dose
 Cross-tolerance: Development of tolerance to
one drug causes tolerance to related drugs. This
may be due to altered metabolism resulting from
chronic drug use. (usually same type of drug
category)
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Tolerance
Discussion
Why would a drug with a relatively
narrow margin of safety be approved by
the FDA for clinical use? Give an example.
 Discuss in your group what might be
examples when a high potency drugs
could be self-medicated and low potency
drugs that must be given under medical
supervision.
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Drug Dependence
Physical
Dependence
(e.g.,withdrawal
and rebound)
vs.
Psychological
Dependence
(e.g., craving)
Psychological Factors Affecting
Drug Effect

Individual’s mental set – The setting, or total
environment, in which a drug is taken may
modify its effect (Individual’s personality, past
history of drug use, social experience, attitudes toward
the drug , etc)
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Placebo effects – The psychological factors
that influence the responses of drugs
independent of their pharmacological
properties
Addiction and Abuse

The use of the term addiction is sometimes
confusing. It is often used interchangeably
with dependence, either physiological or
psychological in nature; other times, it is
used synonymously with the term drug
abuse. A more accurate definition is the
compulsive drug use despite negative
consequences
Addiction and Abuse (continued)
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Factors affecting variability in
dependence/addiction
◦ Hereditary factors (genetic variants);
responsible for 40–60% vulnerability
◦ Drug craving – the intense desire for
drugs, considered a distinct phenomenon
of withdrawal.
Addiction and Abuse (continued)
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Other factors contributing to drug use
patterns
◦ Positive versus negative effects of drug
◦ Peer pressure
◦ Home, school, and work environment
◦ Mental state
End of Presentation