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P A R T 2
Chemotherapeutic agents
may examine stool for ova and parasites. Microscopic
examination of other samples is also used to detect
fungal and protozoal infections. The correct identi-
fication of the organism causing the infection is an
important first step in determining which anti-infective
drug should be used.
Sensitivity of the pathogen
In many situations, healthcare providers use a broad-
spectrum anti-infective agent that has been shown
likely to be most effective in treating an infection with
certain presenting signs and symptoms. In other cases of
severe infection, a broad-spectrum antibiotic is started
after a culture is taken but before the exact causative
organism has been identified. Again, experience influ-
ences selection of the drug, based on the presenting signs
and symptoms. In many cases, it is necessary to perform
sensitivity testing
on the cultured microbes to evaluate
bacteria and determine which drugs are capable of
controlling the particular microorganism. This testing
is especially important with microorganisms that have
known resistant strains. In these cases, culture and sen-
sitivity testing identify the causal pathogen and the most
appropriate drug for treating the infection.
Combination therapy
In some situations, a combination of two or more
types of drugs effectively treats the infection. When the
offending pathogen is known, combination drugs may
be effective in interfering with its cellular structure in
different areas or developmental phases.
Combination therapy may be used for several
reasons:
• The healthcare provider may be encouraged to use a
smaller dose of each drug, leading to fewer adverse
effects but still having a therapeutic impact on the
pathogen.
• Some drugs are synergistic, which means that they
are more powerful when given in combination.
• Many microbial infections are caused by more than
one organism, and each pathogen may react to a
different anti-infective agent.
• Sometimes, the combined effects of the different
drugs delay the emergence of resistant strains.
This is important in the treatment of tuberculosis
(a mycobacterial infection), malaria (a protozoal
infection), HIV infection (a viral infection) and
some bacterial infections. Resistant strains may be
more likely to emerge when fixed combinations are
used over time; however, this may be prevented by
individualising the combination.
Prophylaxis
Sometimes it is clinically useful to use anti-infectives as
a means of
prophylaxis
to prevent infections before they
occur. For example, when people anticipate travelling
to an area where malaria is endemic, they may begin
taking antimalarial drugs before the journey and peri-
odically during the trip. People who are undergoing
gastrointestinal (GI) or genitourinary surgery, which
might introduce bacteria from those areas into the
system, often have antibiotics ordered immediately
after the surgery and periodically thereafter, as appro-
priate, to prevent infection. People with known cardiac
valve disease, valve replacements and other conditions
are especially prone to the development of subacute
bacterial endocarditis because of the vulnerability of
their heart valves. These people use prophylactic anti-
biotic therapy as a precaution when undergoing invasive
procedures, including dental work. Refer to the RHD
Australia, National Heart Foundation of Australia and
the Cardiac Society of Australia and New Zealand rec-
ommended schedule for this prophylaxis.
KEY POINTS
■■
Resistance of a pathogen to an anti-infective agent
can be natural (the pathogen does not use the process
on which the anti-infective works) or acquired
(the pathogen develops a process to oppose the
anti-infective agent).
■■
The emergence of resistant strains is a serious public
health problem. Healthcare providers need to be
alert to prevent the emergence of resistant strains
by not using antibiotics inappropriately, assure that
the anti-infective is taken at a high enough dose for
a long enough period of time, and avoid the use of
newer, powerful anti-infectives if other drugs would
be just as effective.
Adverse reactions to anti-infective therapy
Because anti-infective agents affect cells, it is always
possible that the host cells will also be damaged (see
Box 8.5). No anti-infective agent has been developed
that is completely free of adverse effects. The most
commonly encountered adverse effects associated with
the use of anti-infective agents are direct toxic effects on
the kidney, GI tract and nervous system. Hypersensitiv-
ity reactions and superinfections can also occur.
Kidney damage
Kidney damage occurs most frequently with drugs that
are metabolised by the kidney and then eliminated in
the urine. Such drugs, which have a direct toxic effect
on the fragile cells in the kidney, can cause conditions
ranging from renal dysfunction to full-blown renal
failure. When people are taking these drugs (e.g. amino-
glycosides), they should be monitored closely for any
sign of renal dysfunction. To prevent any accumulation
of the drug in the kidney, people should be well hydrated
throughout the course of the drug therapy.
KEY POINTS
