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P A R T 2
Chemotherapeutic agents
A
nti-infective agents are drugs designed to target foreign
organisms that have invaded and infected the body of
a human host. For centuries, people have used various
naturally occurring chemicals in an effort to treat
disease. Often this was a random act that proved useful.
For instance, the ancient Chinese found that applying
mouldy soybean curds to boils and infected wounds
helped prevent infection or hastened cure. Their finding
was, perhaps, a forerunner to the penicillins used today.
The use of drugs to treat systemic infections is a rela
tively new concept, beginning with Paul Ehrlich in the
1920s. Ehrlich’s research to develop a synthetic chemical
that would be effective only against infection-causing
cells, not human cells, led the way for the scientific
investigation of anti-infective agents. In the late 1920s,
scientists discovered penicillin in a mould sample; in
1935, the sulfonamides were introduced. Since then, the
number of anti-infectives available for use has grown
tremendously. However, many of the organisms these
drugs were designed to treat are rapidly adapting to
repel the effects of anti-infectives, and, therefore, much
work remains to deal with these emergent strains.
ANTI-INFECTIVE AGENTS
Although anti-infective agents target foreign organ-
isms infecting the body of a human host, they do not
possess
selective toxicity
,
which is the ability to affect
certain proteins or enzyme systems used by the infecting
organism but not by human cells. Because all living cells
are somewhat similar, however, no anti-infective drug
has yet been developed that does not affect the host.
This chapter focuses on the principles involved in
the use of anti-infective therapy, and presents some anti-
infectives as examples of these principles. The following
chapters discuss specific agents used to treat particular
infections: antibiotics for bacterial infections; antivirals;
antifungals; antiprotozoals for infections caused by
specific protozoa, including malaria; and anthelmin
tics for infections caused by worms. The final chapter
in this section discusses antineoplastics—drugs used
for treating diseases caused by abnormal cells such as
cancers. Antineoplastics specifically affect human cells
to cause cell death or prevent cell growth and reproduc-
tion. The effects of anti-infectives on various age groups
are discussed in Box 8.1.
Therapeutic actions
Anti-infective agents may act on the cells of invading
organisms in several different ways. The goal is inter-
ference with the normal function of the invading
organism to prevent it from reproducing and to cause
cell death without affecting host cells. Various mecha-
nisms of action are briefly described here and shown in
Figure 8.1. The specific mechanism of action for each
drug class is discussed in the chapters that follow.
• Some anti-infectives interfere with biosynthesis of
the bacterial cell wall. Because bacterial cells have a
slightly different composition than human cells, this
is an effective way to destroy the bacteria without
BOX 8.1
Drug therapy across the lifespan
This box presents general principles of use of anti-
infectives across the lifespan. Specifics for each type
of anti-infective agent are discussed in their respective
chapters within this unit.
Anti-infective agents
CHILDREN
Use anti-infectives with caution; early exposure can lead to
early sensitivity.
Controversy is widespread regarding the use of
antibiotics to treat ear infections, a common paediatric
problem. Some believe that the habitual use of antibiotics
for what might well be a viral infection has contributed
greatly to the development of resistant strains.
Because children can have increased susceptibility
to the gastrointestinal and nervous system effects of
anti-infectives, monitor hydration and nutritional status
carefully.
ADULTS
Adults often demand anti-infectives for a “quick cure”
of various signs and symptoms. Drug allergies and the
emergence of resistant strains can be a big problem with
this group.
PREGNANCY AND BREASTFEEDING
Women who are pregnant or breastfeeding must exercise
extreme caution in the use of anti-infectives. Many anti-
infectives can affect the fetus and also cross into breast
milk, leading to toxic effects in the neonate.
OLDER ADULTS
Older people often do not present with the same signs and
symptoms of infection that are seen in younger people.
Culture and sensitivity tests are important to determine
the type and extent of many infections.
The older person is susceptible to severe adverse
gastrointestinal, renal and neurological effects and must
be monitored for nutritional status and hydration during
drug therapy.
Anti-infectives that adversely affect the liver and
kidneys must be used with caution in older people, who
may have decreased organ function.
