C H A P T E R 9
Antibiotics
91
M
any new bacteria appear each year, and researchers
are challenged to develop new
antibiotics
—chemicals
that inhibit specific bacteria—to deal with each new
threat. Antibiotics are made in three ways: by living
microorganisms, by synthetic manufacture, and, in some
cases, through genetic engineering. Antibiotics may either
be bacteriostatic (preventing the growth of bacteria) or
bactericidal (killing bacteria directly), although several
antibiotics are both bactericidal and bacteriostatic,
depending on the concentration of the particular drug.
This chapter discusses the major classes of antibiotics:
aminoglycosides, carbapenems, cephalosporins, fluoro-
quinolones, penicillins and penicillinase-resistant drugs,
sulfonamides, tetracyclines and the disease-specific
antimycobacterials, including the antitubercular and lep-
rostatic drugs. Antibiotics that do not fit into the large
antibiotic classes include lincosamides, macrolides and
monobactams. Figures 9.1 and 9.2 show sites of cellular
action of these classes of antibiotics.
BACTERIA AND ANTIBIOTICS
Bacteria can invade the human body through many
routes: for example, respiratory, gastrointestinal (GI)
and skin. Once the bacteria invade the body, the human
immune response is activated, and signs and symptoms
of an infection occur as the body tries to rid itself of
the foreign cells. Fever, lethargy, slow-wave sleep induc-
tion and the classic signs of inflammation (e.g. redness,
swelling, heat and pain) all indicate that the body is
responding to an invader. The body becomes the host
for the bacteria and supplies proteins and enzymes
the bacteria need for reproduction. Unchallenged,
the invading bacteria can multiply and send out other
bacteria to further invade tissue.
The goal of antibiotic therapy is to decrease the
population of invading bacteria to a point at which
the human immune system can effectively deal with the
invader. To determine which antibiotic will effectively
interfere with the specific proteins or enzyme systems for
treatment of a specific infection, the causative organism
must be identified through a culture. Sensitivity testing
is also done to determine the antibiotic to which that
particular organism is most sensitive (e.g. which anti
biotic best kills or controls the bacteria).
Gram-positive
bacteria are those whose cell walls
retain a stain known as Gram’s stain or resist decol-
ourisation with alcohol during culture and sensitivity
testing. Gram-positive bacteria are commonly associated
with infections of the respiratory tract and soft tissues.
An example of a gram-positive bacterium is
Strepto-
coccus pneumoniae
, a common cause of pneumonia.
In contrast,
gram-negative
bacteria are those whose
cell walls lose a stain or are decolourised by alcohol.
These bacteria are frequently associated with infections
of the genitourinary (GU) or GI tract. An example of a
gram-negative bacterium is
Escherichia coli
, a common
cause of cystitis.
Aerobic
bacteria depend on oxygen for
Penicillins
continued
dicloxacillin
flucloxacillin
phenoxymethylpenicillin
benzathine
phenoxymethylpenicillin
potassium
procaine penicillin
Broad-spectrum penicillins
amoxycillin
ampicillin
piperacillin
ticarcillin
SULFONAMIDES
sulfadiazine
sulfamethoxazole
sulfasalazine
TETRACYCLINES
doxycycline
minocycline
tetracycline
tigecycline
ANTIMYCOBACTERIALS
Antituberculosis drugs
ethambutol
isoniazid
rifampicin
Leprostatic drugs
clofazimine
dapsone
OTHER ANTIBIOTICS
Lincosamides
clindamycin
lincomycin
Macrolides
azithromycin
clarithromycin
erythromycin
roxithromycin
Monobactams
aztreonam
NEW CLASSES OF ANTIBIOTICS
AND ADJUNCTS
New classes of antibiotics
daptomycin
linezolid
Adjuncts to antibiotic therapy
clavulanic acid
thalidomide
Safe medication administration
Many antibiotics used to treat childhood infections, such
as otitis media and other upper respiratory tract infections
(URTIs), come in an oral suspension, suitable for children.
The order for these solutions is usually written in mLs for
the convenience of the parent who will be dispensing the
medication. It is very important to make sure that the parent
understands that the teaspoon in the prescription refers to
a measuring teaspoon (5 mL). Inadvertent overdoses have
been reported when parents used a kitchen teaspoon to
measure out the child’s dose. Kitchen teaspoons vary greatly
in volume. If a parent calls to report that the medicine is all
gone on day 4 and it was supposed to be given for 7 days,
check to see how the medicine is being measured. Teaching
the parent when the drug is first ordered can prevent
problems during the course of treatment.
