Antimicrobial Drugs

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Chapter 34 Drugs for Bacterial Infections 483
which occur when microorganisms normally present in the
body are destroyed. These normal microorganisms, or host
flora, inhabit the skin and the upper respiratory, genitourinary,
and intestinal tracts. Some of these organisms serve a useful
purpose by producing antibacterial substances and by competing
with pathogenic organisms for space and nutrients.
Removal of host flora by an antibiotic gives the remaining microorganisms
an opportunity to grow, allowing for overgrowth
of pathogenic microbes. Host flora themselves can
cause disease if allowed to proliferate without control, or if
they establish colonies in abnormal locations. For example
E. coli is part of the host flora in the colon but can become a
serious pathogen if it enters the urinary tract. Host flora may
also become pathogenic if the patient’s immune system becomes
suppressed. Microbes that become pathogenic when
the immune system is suppressed are called opportunistic organisms.Viruses
such as the herpes virus, and fungi are examples
of opportunistic organisms that exist on the human body
but may become pathogenic if normal flora are suppressed.
Superinfection should be suspected if a new infection appears
while the patient is receiving anti-infective therapy.
Signs and symptoms of a superinfection commonly include
diarrhea, bladder pain, painful urination, or abnormal vaginal
discharges. Broad-spectrum antibiotics are more likely
to cause superinfections because they kill so many different
species of microorganisms.
34.7 Host Factors
The most important factor in selecting an appropriate antibiotic
is to be certain that the microbe is sensitive to the effects
of the drug. However, the nurse must also take into
account certain host factors that can influence the success of
antibacterial chemotherapy.
The primary goal of antibiotic therapy is to kill enough
bacteria, or to slow the growth of the infection, so that natural
body defenses can overcome the invading agent. Unless an
infection is highly localized, the antibiotic alone may not be
enough: The patient’s immune system and phagocytic cells
will be needed to completely rid the body of the infectious
agent. Patients with suppressed immune systems may require
aggressive antibiotic therapy with bacteriocidal agents. These
patients include those with AIDS and those being treated
with immunosuppressive or antineoplastic drugs. Because
therapy is more successful when the number of microbes is
small, antibiotics may be given on a prophylactic basis to patients
whose white blood cell (WBC) count is extremely low.
Local conditions at the infection site should be considered
when selecting an antibiotic because factors that hinder
the drug from reaching microbes will limit therapeutic
success. Infections of the central nervous system are particularly
difficult to treat because many drugs cannot cross the
blood–brain barrier. Injury or inflammation can cause tissues
to become acidic or anaerobic and to have poor circulation.
Excessive pus formation or hematomas can block
drugs from reaching their targets. Although most bacteria
are extracellular in nature, pathogens such as
Mycobacterium tuberculosis, salmonella, toxoplasma, and
listeria may reside intracellularly and thus be difficult for
anti-infectives to reach in high concentrations. Consideration
of these factors may necessitate a change in the route of
drug administration or the selection of a more effective antibiotic
specific for the local conditions.
Severe allergic reactions to antibiotics, while not common,
may be fatal. The nurse’s initial patient assessment
must include a thorough drug history and a description of
any reactions to those drugs. A previous acute allergic incident
is highly predictive of future hypersensitivity. If severe
allergy to an anti-infective is established, it is best to avoid
all drugs in the same chemical class. Because the patient may
have been exposed to an antibiotic unknowingly, through
food products or molds, allergic reactions can occur without
previous incident. Penicillins are the class of antibacterials
having the highest incidence of allergic reactions;
between 0.7% and 4% of all patients who receive them exhibit
some degree of hypersensitivity.
Other host factors to be considered are age, pregnancy
status, and genetics. The very young and the very old are often
unable to readily metabolize or excrete antibiotics; thus,
doses are generally decreased. Some antibiotics cross the
placenta. For example, tetracyclines taken by the mother
can cause teeth discoloration in the newborn; aminoglycosides
can affect the infant’s hearing. The benefits of antibiotic
use in pregnant or lactating women must be carefully
weighed against the potential risks to the fetus and neonate.
Lastly, some patients have a genetic absence of certain enzymes
used to metabolize antibiotics. For example, patients
with a deficiency of the enzyme glucose-6-phosphate dehydrogenase
should not receive sulfonamides, chloramphenicol,
or nalidixic acid because their erythrocytes may
rupture.
ANTIBACTERIAL AGENTS
Antibacterial agents are derived from a large number of
chemical classes. Although drugs within a class have similarities
in their mechanisms and spectrum of activity, each
is slightly different, and learning the differences and therapeutic
applications among antibacterial agents can be
challenging. Basic nursing assessments and interventions
TREATING THE DIVERSE PATIENT
Hispanic Cultural Beliefs and Antibacterials
Certain ethnic groups,such as Hispanics,believe that illness is caused by an imbalance
in hot and cold.In a healthy individual, hot and cold are in balance; when an
imbalance occurs,disease results.
Illnesses are classified as either hot or cold as well.For example,sore throat and
diarrhea are considered hot diseases; colds, upper respiratory infections, arthritis,
and rheumatism are considered cold diseases. Traditional treatment in such cultures
is to restore the body’s balance through the addition or subtraction of herbs,
foods,or medications that are classified as either hot or cold.To treat a hot disease,
medications or herbs considered cold are used.For example,penicillin is considered
a hot medicine, but amoxicillin is less hot. Using acetaminophen with amoxicillin
makes it cooler.
# 102887 Cust: PE/NJ/CHET Au: ADAMS Pg. No. 483
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