C H A P T E R 8
Anti-infective agents
85
Preventing resistance
Because the emergence of resistant strains of microbes is
a serious public health problem that continues to grow,
healthcare providers must work together to prevent the
emergence of resistant pathogens. Exposure to an anti-
microbial agent leads to the development of resistance,
so it is important to limit the use of antimicrobial agents
to the treatment of specific pathogens known to be sen-
sitive to the drug being used.
Drug dosing is important in preventing the develop
ment of resistance. Doses should be high enough and
the duration of drug therapy should be long enough to
eradicate even slightly resistant microorganisms. The
recommended dosage for a specific anti-infective agent
takes this issue into account. Around-the-clock dosing
eliminates the peaks and valleys in drug concentration
and helps to maintain a constant therapeutic level to
prevent the emergence of resistant microbes during times
of low concentration. The duration of drug use is critical
to ensure that the microbes are completely, not partially,
eliminated and are not given the chance to grow and
develop resistant strains. It has proved to be difficult
to convince people who are taking anti-infective drugs
that the timing of doses and the length of time they
continue to take the drug are important. Many people
stop taking a drug once they start to feel better and then
keep the remaining pills to treat themselves at some time
in the future when they do not feel well. This practice
favours the emergence of resistant strains. Box 8.4 gives
tips on teaching about this.
Healthcare providers should also be cautious about
the indiscriminate use of anti-infectives. Antibiotics
are not effective in the treatment of viral infections
or illnesses such as the common cold. However, many
people seek prescriptions for these drugs when they visit
practitioners because they are convinced that they need
to take something to feel better. Healthcare providers
who prescribe anti-infectives without knowing the caus-
ative organism and which drugs might be appropriate
are promoting the emergence of resistant strains of
microbes. With many serious illnesses, including pneu-
monias for which the causative organism is suspected,
antibiotic therapy may be started as soon as a sample of
the bacteria, or
culture
, is taken and before the results
are known. Healthcare providers also tend to try newly
introduced, more powerful drugs when a more estab-
lished drug may be just as effective. Use of a powerful
drug in this way leads to the rapid emergence of resistant
strains to that drug, perhaps limiting its potential use-
fulness when it might be truly necessary.
KEY POINTS
■■
The goal of anti-infective therapy is the reduction
of the invading organisms to a point at which
the human immune response can take care of the
infection.
■■
Anti-infectives can act to destroy an infective
pathogen (bactericidal) or to prevent the pathogen
from reproducing (bacteriostatic).
■■
Anti-infectives can have a small group of pathogens
against which they are effective (narrow spectrum),
or they can be effective against many pathogens
(broad spectrum).
Using anti-infective agents
Anti-infective agents are used to treat systemic infec-
tions and sometimes as a means of prophylaxis (to
prevent infections before they occur).
Treatment of systemic infections
Many infections that once led to lengthy, organ-damaging
or even fatal illnesses are now managed quickly and effi-
ciently with the use of systemic anti-infective agents.
Before the introduction of penicillin to treat strepto
coccal infections, many people developed rheumatic
fever with serious cardiac complications. Today, rheu-
matic fever and the resultant cardiac valve defects are
seldom seen. Several factors should be considered before
beginning one of these chemotherapeutic regimens
to ensure that the person obtains the greatest benefit
possible with the fewest adverse effects. These factors
include identification of the correct pathogen and selec-
tion of a drug that is most likely to (1) cause the least
complications for that person and (2) be most effective
against the pathogen involved.
Identification of the pathogen
Identification of the infecting pathogen is done by cul-
turing a tissue sample from the infected area. Bacterial
cultures are performed in a laboratory, in which a swab
of infected tissue is allowed to grow on an agar plate.
Staining techniques and microscopic examination are
used to identify the offending bacterium. When investi
gators search for parasitic sources of infection, they
KEY POINTS
Using anti-infective agents
When teaching people who are prescribed an anti-
infective agent, it is important to always include some
general points:
• This drug is prescribed for treating the particular
infection that you have now. Do not use this drug to
treat other infections.
• This drug needs to be taken as prescribed—for the
correct number of times each day and for the full
number of days. Do not stop taking the drug if you start
feeling better.You need to take the drug for the full
number of treatment days to ensure that the infection
has been destroyed.
Individual and family teaching
BOX 8.4
