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P A R T 2
Chemotherapeutic agents
Praziquantel is taken in a series of three oral doses at
4- to 6-hour intervals. It is rapidly absorbed from the GI
tract and reaches peak plasma levels within 1 to 3 hours.
It is metabolised in the liver with a half-life of 0.8 to
1.5 hours. Excretion of praziquantel occurs primarily
through the urine.
Pyrantel is poorly absorbed, and most of the drug
is excreted unchanged in the faeces, although a small
amount may be found in the urine.
Contraindications and cautions
Overall contraindications to the use of anthelmintic
drugs include the presence of known allergy to any of
these drugs; breastfeeding
because the drugs can enter
breast milk and could be toxic to the infant
—women
are advised to refrain from breastfeeding when using
these drugs; and pregnancy (in most cases)
because
of reported associated fetal abnormalities or death.
Women of childbearing age should be advised to use
barrier contraceptives while taking these drugs. Pyrantel
has not been established as safe for use in children
younger than 2 years. Albendazole should be used only
after the causative worm has been identified
because it
can cause adverse effects on the liver, which could be
problematic if the person has liver involvement.
Use caution in the presence of renal or hepatic
disease
that interferes with the metabolism or excretion
of drugs that are absorbed systemically
and in cases
of severe diarrhoea and malnourishment,
which could
alter the effects of the drug on the intestine and any
pre-existing helminths.
Adverse effects
Adverse effects frequently encountered with the use of
these anthelmintic agents are related to their absorp-
tion or direct action in the intestine. Mebendazole and
pyrantel, which are not absorbed systemically, may cause
abdominal discomfort, diarrhoea or pain but have very
few other effects and are well tolerated. Anthelmintics
that are absorbed systemically may cause the following
effects: headache and dizziness; fever, shaking, chills
and malaise associated with an immune reaction to the
death of the worms; rash; pruritus; and loss of hair.
Renal failure and severe bone marrow depression
are associated with albendazole, which is toxic to some
human tissues. People taking this drug require careful
monitoring.
Clinically important drug–drug interactions
The effects of albendazole, which are already severe,
may increase if the drug is combined with dexameth-
asone, praziquantel or cimetidine. These combinations
should be avoided if at all possible; if they are necessary,
people should be monitored closely for the occurrence of
adverse effects.
Prototype summary: Mebendazole
Indications:
Treatment of whipworm, pinworm,
roundworm and hookworm infections.
Actions:
Irreversibly blocks glucose uptake by
susceptible helminths, depleting glycogen stores
needed for survival and reproduction, causing the
death of the helminth.
Pharmacokinetics:
Route
Onset
Peak
Oral
Slow
2–4 hours
T
1/2
:
2.5 to 9 hours; metabolised in the liver and
excreted in the faeces.
Adverse effects:
Transient abdominal pain,
diarrhoea, fever.
Care considerations for
people receiving anthelmintics
Assessment: History and examination
■
■
Assess for possible contraindications or cautions:
history of allergy to any of the anthelmintics
to
avoid hypersensitivity reactions
; history of hepatic
or renal dysfunction
that might interfere with drug
metabolism and excretion of the drug
; and current
status related to pregnancy and breastfeeding,
which are contraindications to the use of these
drugs
.
■
■
Perform a physical assessment
to establish baseline
data for determining the effectiveness of the
drug and the occurrence of any adverse effects
associated with drug therapy
.
■
■
Obtain a culture of stool for ova and parasites
to determine the infecting worm and establish
appropriate treatment
.
■
■
Examine reflexes and muscle strength
to evaluate
changes that occur as a result of drug therapy
.
■
■
Evaluate liver function and renal function tests
to determine appropriateness of therapy and to
monitor for toxicity
.
■
■
Examine skin, including colour, temperature and
texture, and note any lesions to assess for possible
adverse effects.
■
■
Assess the abdomen
to evaluate for any changes
from baseline related to the infection, identify
possible adverse effects and monitor for
improvement
.
Implementation with rationale
■
■
Arrange for appropriate culture and sensitivity tests
before beginning therapy
to ensure identification
