C H A P T E R 2
Drugs and the body
29
into any plan of care so that obvious problems can be
spotted and handled promptly. If a drug just does not
do what it is expected to do, further examine the factors
that are known to influence drug effects (Box 2.2). Fre
quently, the drug regimen can be modified to deal with
that influence. Rarely is it necessary to completely stop
a needed drug regimen because of adverse or intolerable
effects. In many cases, the nurse is the caregiver in the
best position to assess problems early.
CHAPTER SUMMARY
■■
Pharmacodynamics is the study of the way that drugs
affect the body.
■■
Most drugs work by replacing natural (endogenous)
chemicals, by stimulating normal cell activity or by
depressing normal cell activity.
■■
Chemotherapeutic agents work by interfering with
normal cell functioning, causing cell death. The
most desirable chemotherapeutic agents are those
with selective toxicity to foreign cells and foreign cell
activities.
■■
Drugs frequently act at specific receptor sites on cell
membranes to stimulate enzyme systems within the
cell and to alter the cell’s activities.
■■
Pharmacokinetics—the study of the way the body
deals with drugs—includes absorption, distribution,
biotransformation and excretion of drugs.
■■
The goal of established dosing schedules is to achieve
an effective concentration of the drug in the body.
This effective concentration is the amount of the
drug necessary to achieve the drug’s therapeutic
effects.
■■
Arriving at an effective concentration involves
a dynamic equilibrium among the processes of
drug absorption, distribution, metabolism or
biotransformation and excretion.
■■
Absorption involves moving a drug into the body
for circulation. Oral drugs are absorbed from the
small intestine, undergo many changes and are
affected by many things in the process. IV drugs are
injected directly into the circulation and do not need
additional absorption.
■■
Drugs are distributed to various tissues throughout
the body depending on their solubility and ionisation.
Most drugs are bound to plasma proteins for
transport to responsive tissues.
■■
Drugs are metabolised or biotransformed into less
toxic chemicals by various enzyme systems in the
body. The liver is the primary site of drug metabolism
or biotransformation. The liver uses the cytochrome
P450 enzyme system to alter the drug and start its
biotransformation.
■■
The first-pass effect is the breakdown of oral drugs in
the liver immediately after absorption. Drugs given
by other routes often reach responsive tissues before
passing through the liver for biotransformation.
■■
Drug excretion is removal of the drug from the body.
This occurs mainly through the kidneys.
■■
The half-life of a drug is the period of time it takes
for an amount of drug in the body to decrease to half
of the peak level it previously achieved. The half-
life is affected by all aspects of pharmacokinetics.
Knowing the half-life of a drug helps in predicting
dosing schedules and duration of effects.
■■
The actual effects of a drug are determined by its
pharmacokinetics, its pharmacodynamics and many
human factors that can change the drug’s effectiveness.
■■
To provide the safest and most effective drug therapy,
the nurse or midwife must consider all of the possible
factors that influence drug concentration and
effectiveness.
Knowing your strengths and weaknesses helps you to
study more effectively. Take a PrepU Practice Quiz
to find out how you measure up!
ONLINE RESOURCES
An extensive range of additional resources to enhance teaching
and learning and to facilitate understanding of this chapter may
be found online at the text’s accompanying website, located on
thePoint at
These include Watch and
Learn videos, Concepts in Action animations, journal articles,
review questions, case studies, discussion topics and quizzes.
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