C H A P T E R 9
Antibiotics
123
CHAPTER SUMMARY
■■
Antibiotics work by disrupting protein or
enzyme systems within a bacterium, causing cell
death (bactericidal) or preventing multiplication
(bacteriostatic).
■■
The proteins or enzyme systems affected by
antibiotics are more likely to be found or used in
bacteria than in human cells.
■■
The primary therapeutic use of each antibiotic is
determined by the bacterial species that are sensitive
to that drug, the clinical condition of the person
receiving the drug and the benefit-to-risk ratio for
the person.
■■
The longer an antibiotic has been available, the more
likely it is that mutant bacterial strains resistant
to the mechanisms of antibiotic activity will have
developed.
■■
The most common adverse effects of antibiotic
therapy involve the GI tract (nausea, vomiting,
diarrhoea, anorexia, abdominal pain) and
superinfections (invasion of the body by normally
occurring microorganisms that are usually kept in
check by the normal flora).
■■
To prevent or contain the growing threat of drug-
resistant strains of bacteria, it is very important to
use antibiotics cautiously, to complete the full course
of an antibiotic prescription and to avoid saving
antibiotics for self-medication in the future. A person
and family teaching program should address these
issues, as well as the proper dosing procedure for
the drug (even if the person feels better) and the
importance of keeping a record of any reactions to
antibiotics.
Knowing your strengths and weaknesses helps you to
study more effectively. Take a PrepU Practice Quiz
to find out how you measure up!
Prototype summary: Clindamycin
Indications:
Treatment of serious infections caused
by susceptible strains of bacteria, including some
anaerobes; useful in septicaemia and chronic bone
and joint infections.
Actions:
Inhibits protein synthesis in susceptible
bacteria, causing cell death.
Pharmacokinetics:
Route Onset
Peak
Duration
Oral
Varies
1–2 hours 8–12 hours
IM 20–30 minutes 1–3 hours 8–12 hours
IV Immediate
Minutes
8–12 hours
Topical Minimal absorption
T
1/2
:
2 to 3 hours; metabolised in the liver, excreted
in the urine and faeces.
Adverse effects:
Nausea, vomiting, diarrhoea,
pseudomembranous colitis, bone marrow
suppression, hypotension, cardiac arrest with rapid
IV infusion, rash, pain on injection, abscess at
injection site.
Prototype summary: Aztreonam
Indications:
Treatment of lower respiratory,
dermatological, urinary tract, intra-abdominal,
and gynaecological infections caused by susceptible
strains of gram-negative bacteria.
Actions:
Interferes with bacterial cell wall synthesis,
causing cell death in susceptible gram-negative
bacteria; is not effective against gram-positive or
anaerobic bacteria.
Pharmacokinetics:
Route Onset
Peak
Duration
IM Varies
60–90 minutes 6–8 hours
IV Immediate 30 minutes
6–8 hours
T
1/2
:
1.5 to 2 hours; excreted unchanged in the urine.
Adverse effects:
Nausea, vomiting, diarrhoea, rash,
superinfection, anaphylaxis, local discomfort at
injection sites.
Prototype summary: Erythromycin
Indications:
Treatment of respiratory,
dermatological, urinary tract and GI infections
caused by susceptible strains of bacteria.
Actions:
Binds to cell membranes, causing a
change in protein function and cell death; can
be bacteriostatic or bactericidal.
Pharmacokinetics:
Route
Onset
Peak
Oral
1–2 hours
1–4 hours
IV
Rapid
1 hour
T
1/2
:
3 to 5 hours; metabolised in the liver, excreted
in bile and urine.
Adverse effects:
Abdominal cramping, vomiting,
diarrhoea, rash, superinfection, liver toxicity,
risk for pseudomembranous colitis, potential for
hearing loss.
