C H A P T E R 3
Toxic effects of drugs
33
Hypersensitivity
Some people are excessively responsive to either the
primary or the secondary effects of a drug. This is known
as
hypersensitivity
and it may result from a pathological
or underlying condition. For example, many drugs are
excreted through the kidneys; a person who has kidney
problems may not be able to excrete the drug and may
accumulate the drug in the body, causing toxic effects.
The person will exhibit exaggerated adverse effects
from a standard dose of the medication because of the
accumulation of the drug. In some cases, individuals
exhibit increased therapeutic and adverse effects with no
definite pathological condition. Each person has slightly
different receptors and cellular responses. Frequently
older people will react to narcotics with increased stim
ulation and hyperactivity, not with the sedation that is
expected. It is thought that this response is related to
a change in receptors with age, leading to an increased
sensitivity to a drug’s effects.
Hypersensitivity can also occur if a person has an
underlying condition that makes the drug’s effects espe
cially unpleasant or dangerous. For example, a person
with an enlarged prostate who takes an anticholinergic
drug may develop urinary retention or even bladder
paralysis when the drug’s effects block the urinary
sphincters. This person needs to be taught to empty the
bladder before taking the drug. A reduced dose may
also be required to avoid potentially serious effects on
the urinary system.
DRUG ALLERGY
A
drug allergy
occurs when the body forms antibod
ies to a particular drug, causing an immune response
when the person is re-exposed to the drug. This is con
sidered an “unpredictable side effect”. A person cannot
be allergic to a drug that has never been taken, although
people can have cross-allergies to drugs within the same
drug class as one formerly taken. Many people state
that they have a drug allergy because of the effects of
a drug. For example, one woman stated that she was
allergic to the diuretic frusemide (
Lasix
). On further
questioning, the nurse or midwife discovered that the
woman was “allergic” to the drug because it made her
urinate frequently—the desired drug effect, but one that
the woman thought was a reaction to the drug. Ask
additional questions of people who state that they have
a drug “allergy” to ascertain the exact nature of the
response and whether or not it is a true drug allergy.
Many people do not receive needed treatment because
the response to the drug is not understood.
Drug allergies fall into four main classifications:
anaphylactic reactions, cytotoxic reactions, serum
sickness and delayed reactions (see Table 3.1). Nurses
and midwives involved in administering drugs must con
stantly assess for potential drug allergies and must be
prepared to intervene appropriately.
KEY POINTS
■■
All drugs have effects other than the desired
therapeutic effect.
■■
Primary actions of the drug can be extensions of the
desired effect.
■■
Secondary actions of a drug are effects that the
drug causes in the body that are not related to the
therapeutic effect.
■■
Hypersensitivity reactions to a drug are individual
reactions that may be caused by increased sensitivity
to the drug’s therapeutic or adverse effects.
■■
Drug allergies occur when a person develops
antibodies to a drug after exposure to the drug.
DRUG-INDUCED TISSUE AND ORGAN
DAMAGE
Drugs can act directly or indirectly to cause many types
of adverse effects in various tissues, structures and
organs (see Figure 3.1). These drug effects account for
many of the cautions that are noted before drug admini
stration begins. The possibility that these effects can
occur also accounts for the contraindications for the
use of some drugs in people with a particular history
or underlying pathology. The specific contraindications
and cautions for the administration of a given drug are
noted with each drug type discussed in this book and in
the individual monographs found in various drug guides.
These effects occur frequently enough that the nurse or
midwife should be knowledgeable about the presenta
tion of the drug-induced damage and about appropriate
interventions to be used should they occur.
Dermatological reactions
Dermatological reactions
are adverse reactions involving
the skin. These can range from a simple rash to poten
tially fatal exfoliative dermatitis. Many adverse reactions
involve the skin because many drugs can deposit there
or cause direct irritation to the tissue. In dark-skinned
people, including Indigenous Australians, Ma– ori people
and dark-skinned Africans, careful skin assessment is
needed as such reactions may not be as evident due to
normal pigmentation. For example, redness is not often
evident so assessment will be based upon skin tempera
ture, localised swelling or tightness.
Rashes, hives
Many drugs are known to cause skin reactions. Older
drugs such as procainamide, used in the past to treat
KEY POINTS
