114
P A R T 2
Chemotherapeutic agents
KEY POINTS
■■
Sulfonamides are older drugs; many strains have
developed resistance to the sulfonamides, so they are
no longer widely used.
■■
Monitor the person for CNS toxicity, nausea,
vomiting, diarrhoea, liver injury, renal toxicity and
bone marrow depression.
TETRACYCLINES
The tetracyclines (Table 9.7) were developed as semi
synthetic antibiotics based on the structure of a common
soil mould. They are composed of four rings, which is
how they got their name. Researchers have developed
newer tetracyclines to increase absorption and tissue
penetration. Widespread resistance to the tetracyclines
has limited their use in recent years. Tetracyclines include
doxycycline (
Doryx
,
Frakas
), tigecycline (
Tygacil
) and
minocycline (
Akamin
).
Therapeutic actions and indications
The tetracyclines work by inhibiting protein synthe-
sis in a wide range of bacteria, leading to the inability
of the bacteria to multiply (see Figure 9.2). Because
the affected protein is similar to a protein found in
KEY POINTS
human cells, these drugs can be toxic to humans at high
concentrations.
Tetracyclines are indicated for treatment of infec-
tions caused by
Rickettsiae
,
M. pneumoniae
,
Borrelia
recurrentis
,
H. influenzae
,
Haemophilus ducreyi
,
Pasteurella pestis
,
Pasteurella tularensis
,
Bartonella
bacilliformis
,
Bacteroides
species,
Vibrio comma
,
Vibrio
fetus
,
Brucella
species,
E. coli
,
E. aerogenes
,
Shigella
species,
Acinetobacter calcoaceticus
,
Klebsiella
species,
Diplococcus pneumoniae
and
S. aureus;
against agents
that cause psittacosis, ornithosis, lymphogranuloma
venereum and granuloma inguinale; when penicillin is
contraindicated in susceptible infections; and for treat-
ment of acne and uncomplicated GU infections caused
by
C. trachomatis.
Some of the tetracyclines are also
used as adjuncts in the treatment of certain protozoal
infections. See Table 9.7 for usual indications for each
agent.
Pharmacokinetics
Tetracyclines are absorbed adequately, but not com-
pletely, from the GI tract. Their absorption is affected
by food, iron, calcium and other drugs in the stomach.
Tetracyclines are concentrated in the liver and excreted
unchanged in the urine, with half-lives ranging from
12 to 25 hours. These drugs cross the placenta and pass
into breast milk (see contraindications and cautions).
Tetracycline is available in oral and topical forms,
in addition to being available as an ophthalmic agent.
Doxycycline and minocycline are available in IV and
oral forms.
Contraindications and cautions
Tetracyclines are contraindicated in people with known
allergy to tetracyclines or to tartrazine (e.g. in specific
oral preparations that contain tartrazine) and during
pregnancy and breastfeeding
because of effects on devel-
oping bones and teeth.
The ophthalmic preparation is
contraindicated in people who have fungal, mycobac-
terial or viral ocular infections
because the drug kills
Evaluation
■
■
Monitor person’s response to the drug (resolution
of bacterial infection).
■
■
Monitor for adverse effects (GI effects, CNS
effects, rash and crystalluria).
■
■
Evaluate the effectiveness of the teaching plan
(person can name the drug, dosage, possible
adverse effects to expect and specific measures to
help avoid adverse effects).
■
■
Monitor the effectiveness of comfort and safety
measures and compliance with the regimen.
TABLE 9.7
DRUGS IN FOCUS Tetracyclines
Drug name
Dosage/route
Usual indications
doxycycline (Doryx,
Doxsig, Frakas)
Adult and paediatric >8 years: Initially
200 mg/day PO followed by 100 mg/day PO
Treatment of a wide variety of infections,
including traveller’s diarrhoea and sexually
transmitted diseases; periodontal disease
minocycline (Akamin,
Minomycin)
Adult: 200 mg PO initially, followed by
100 mg/day PO
Treatment of meningococcal carriers and
of various uncomplicated genitourinary
and gynaecological infections
tetracycline (Optycin Eye
Ointment)
Applied to lower conjunctival sac q 2 hours
Ocular infection
tigecycline (Tygacil)
Adult: Initially, 100 mg IV followed by 50 mg IV
q 12 hours
Complicated skin and intra-abdominal
infections, including those with MRSA
