C H A P T E R 5 2
Drugs affecting the urinary tract and the bladder
821
not specific to urinary tract infections and are also used
for treating other infections (see Chapter 9).
The other type of urinary tract anti-infective works
to acidify the urine, killing bacteria that might be in
the bladder. This group includes hexamine hippurate
(
Hiprex
).
Therapeutic actions and indications
Urinary tract anti-infectives act specifically within the
urinary tract to destroy bacteria, either through a direct
antibiotic effect or through
acidification
of the urine.
They do not generally have an antibiotic effect system-
ically, being activated or effective only in the urinary
tract (Figure 52.1). Those drugs with an antibiotic
effect interfere with reproduction of the gram-negative
bacteria and cause bacterial cell death. Those that cause
acidification of the urine produce an environment that is
not conducive to bacterial survival, leading to bacterial
cell death. They are used to treat chronic UTIs, as
adjunctive therapy in acute cystitis and pyelonephritis,
and as prophylaxis with urinary tract anatomical abnor-
malities and residual urine disorders.
See the Critical
thinking scenario for additional information regarding
teaching the person about treatment with hexamine
hippurate for cystitis
.
Table 52.2 discusses usual indications for each of
the urinary tract anti-infectives.
Pharmacokinetics
Norfloxacin, a newer and broader-spectrum drug, is
effective against even more gram-negative strains. This
drug is rapidly absorbed when taken orally and under-
goes hepatic metabolism and renal excretion. The dose
of norfloxacin must also be reduced in the presence of
renal impairment.
Nitrofurantoin is another older drug with a very
short half-life (20 to 60 minutes). It is not effective
against as many gram-negative bacteria as the newer
drugs are, but it has been successfully used for suppres-
sion therapy in adults and children with chronic UTIs.
It is well absorbed when taken orally, metabolised in
the liver and excreted in urine. No dose adjustment is
needed with renal impairment.
Hexamine hippurate, taken orally, is well absorbed,
undergoes metabolism in the liver and is excreted in
urine.
Norfloxacin, nitrofurantoin and hexamine hippu-
rate cross the placenta and enter breast milk.
Contraindications and cautions
These drugs are contraindicated in the presence of any
known allergy to any of these drugs
to prevent hyper-
sensitivity reactions
. They should be used with caution
in the presence of renal dysfunction,
which could inter-
fere with the excretion and action of these drugs,
and
with pregnancy and breastfeeding
because of the poten-
tial for adverse effects on the fetus or neonate.
TABLE 52.2
DRUGS IN FOCUS Urinary tract anti-infectives
Drug name
Dosage/route
Usual indications
hexamine hippurate
(Hiprex)
1 g b.d. PO
Paediatric (6–12 years): 0.5–1 g PO b.d.
Suppression or elimination of bacteriuria
associated with UTIs and anatomical
abnormalities
nitrofurantoin
(Macrodantin)
50–100 mg PO q.i.d. for 10–14 days;
50–100 mg PO at bedtime for chronic
suppressive therapy
Paediatric: 5–7 mg/kg per day in four divided
doses
Treatment of UTIs caused by susceptible
bacteria
norfloxacin (Noroxin,
Roxin)
400 mg q 12 hours PO, length of therapy
dependent on site and intensity of infection
Treatment of UTIs caused by susceptible
bacteria (broad-spectrum agent);
treatment of uncomplicated urethral and
cervical gonorrhoea and prostatitis
Urinary bladder
Ureter
Muscle layer
Endothelial
layer
Fundus of bladder
Epithelial layer
Opening of ureter
Muscle layer
Neck of bladder
Urethral sphincter
Prostate gland
Urethra
Urinary tract
antispasmodics
work here
Urinary tract
analgesics
work here
Urinary tract
anti-infectives
work here
Bladder
protectants
work here
Drugs used
to treat BPH
work here
FIGURE 52.1
Sites of action of drugs acting on the urinary tract.
