C H A P T E R 9
Antibiotics
93
who have severe GI disease or who are debilitated. (See
Box 9.1 for effects of antibiotics across the lifespan.)
The antibiotic of choice is one that affects the causative
organism and leads to the fewest adverse effects for the
person involved.
In some cases, antibiotics are given in combination
because they are
synergistic
; meaning their combined
effect is greater than their effect if they are given indi-
vidually (Box 9.2). Use of synergistic antibiotics also
allows the person to take a lower dose of each antibiotic
to achieve the desired effect, which helps to reduce the
adverse effects that a particular drug may have.
In some situations, antibiotics are used as a means of
prophylaxis, or prevention of potential infection. People
who will soon be in a situation that commonly results in
a specific infection (e.g. people undergoing GI surgical
procedures, which may introduce GI bacteria into the
bloodstream or peritoneum) may be given antibiotics
before they are exposed to the bacteria. Usually a large,
one-time dose of an antibiotic is given to destroy any
bacteria that enters the host immediately and thereby
prevent a serious infection.
BOX 9.1
Drug therapy across the lifespan
Antibiotics
CHILDREN
Children are very sensitive to the gastrointestinal and
central nervous system (CNS) effects of most antibiotics,
and more severe reactions can be expected when these
drugs are used in children. It is important to monitor
the hydration and nutritional status of children who are
adversely affected by drug-induced diarrhoea, anorexia,
nausea and vomiting. Superinfections can be a problem
for small children as well. For example, thrush (oral
candidiasis) is a common super-infection that makes
eating and drinking difficult.
Many antibiotics do not have proven safety and efficacy
in paediatric use, and extreme caution should be used
when giving them to children.The fluoroquinolones,
for instance, are associated with damage to developing
cartilage and are not recommended for growing children.
Paediatric dosages of antibiotics should be double-
checked to make sure that the child is receiving the correct
dose, thereby improving the chance of eradicating the
infection and decreasing the risk of adverse effects.
Antibiotic treatment of ear infections, a common
paediatric problem, is controversial. Ongoing research
suggests that judicious use of decongestants and anti-
inflammatories may be just as successful as the use of
antibiotics without the risk of development of resistant
bacterial strains.
Parents, not wanting to see their child sick, may
demand antibiotics as a cure-all whenever their child is
fussy or feverish. Parent education is very important in
helping to cut down the unnecessary use of antibiotics
in children.
ADULTS
Many adults believe that antibiotics are a cure-all for any
discomfort and fever. It is very important to explain that
antibiotics are useful against only specific bacteria and
actually can cause problems when used unnecessarily for
viral infections, such as the common cold.
Adults need to be cautioned to take the entire course of
the medication as prescribed and not to store unused pills
for future infections or share antibiotics with symptomatic
friends.
PREGNANCY AND BREASTFEEDING
Women who are pregnant or breastfeeding should not
take antibiotics unless the benefit clearly outweighs
the potential risk to the fetus or neonate.Tetracyclines,
for example, are associated with pitting of enamel in
developing teeth and with calcium deposits in growing
bones.These drugs can cause serious problems for
neonates. Women of childbearing age should be advised
to use barrier contraceptives if any of these drugs are
used.
Many antibiotics interfere with the effectiveness of oral
contraceptives and unplanned pregnancies can occur.
OLDER ADULTS
In many instances, older adults do not present with
the same signs and symptoms of infections as other
people.Therefore, assessing the problem and obtaining
appropriate specimens for culture is especially important
with this population.
Older people may be more susceptible to the adverse
effects associated with antibiotic therapy.Their hydration
and nutritional status should be monitored closely, as
should the need for safety precautions if CNS effects occur.
If hepatic or renal dysfunction is expected (particularly in
very old people, those who may depend on alcohol, and
those who are taking other hepatotoxic or nephrotoxic
drugs), the dose may need to be lowered and the person
should be monitored more frequently.
Elderly people also need to be cautioned to complete
the full course of drug therapy, even when they feel better,
and not to save pills for self-medication at a future time.
Clavulanic acid protects certain beta-lactam antibiotics
from breakdown in the presence of penicillinase enzymes.
A combination of amoxycillin and clavulanic acid
(
Augmentin
) is commonly used to allow the amoxycillin
to remain effective against certain strains of resistant
bacteria (usual dosage, 250–500 mg PO q 8 hours
for adults or 20–40 mg/kg/day PO in divided doses
for children). The theory behind the combination of
ticarcillin and clavulanic acid (
Timentin
) is similar
(usual dosage 3.1 g IM q 4–6 hours for adults; safety
not established for children).
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BOX 9.2
Using combination drugs to fight
resistant bacteria
