164
P A R T 2
Chemotherapeutic agents
parts of the world. In our local region, malaria remains a
significant cause of mortality in countries such as Papua
New Guinea and Indonesia. The only known method of
transmission of malaria is through the bite of a female
Anopheles
mosquito
, an insect that harbours the proto-
zoal parasite and carries it to humans.
Four protozoal parasites, all in the genus
Plasmo-
dium
, have been identified as causes of malaria:
•
Plasmodium falciparum
is considered to be the most
dangerous type of protozoan. Infection with this
protozoan results in an acute, rapidly fulminating
disease with high fever, severe hypotension, swelling
and reddening of the limbs, loss of red blood cells and
even death.
•
Plasmodium vivax
causes a milder form of the
disease, which seldom results in death.
•
Plasmodium malariae
is endemic in many tropical
countries and causes very mild signs and symptoms in
the local population. It can cause more acute disease
in travellers to endemic areas.
•
Plasmodium ovale
, which is rarely seen, seems to be
in the process of being eradicated.
A major problem with controlling malaria involves
the mosquito that is responsible for transmitting the
disease, which has developed a resistance to the insecti-
cides designed to eradicate it. Over the years, widespread
efforts at mosquito control were successful, with fewer
cases of malaria being seen each year. However, the rise
of insecticide-resistant mosquitoes has allowed malaria
to continue to flourish, increasing the incidence of the
I
nfections caused by
protozoa
—single-celled organ-
isms that pass through several stages in their life cycles,
including at least one phase as a human parasite—are
very common in several parts of the world. In tropical
areas, where protozoal infections are most prevalent,
many people suffer multiple infestations at the same
time. These illnesses are relatively rare in Australia and
New Zealand, but with people travelling throughout the
world in increasing numbers, it is not unusual to find an
individual who returns home from a trip to Africa, Asia
or South America with fully developed protozoal infec-
tions. Protozoa thrive in tropical climates, but they may
also survive and reproduce in any area where people live
in very crowded and unsanitary conditions. This chapter
focuses on agents used for protozoal infections that are
caused by insect bites (malaria, trypanosomiasis and
leishmaniasis) and those that result from ingestion or
contact with the causal organism (amoebiasis, giardiasis
and trichomoniasis). Box 12.1 discusses the use of anti-
protozoals across the lifespan. Figure 12.1 shows sites of
action for these agents.
MALARIA
Malaria
is a parasitic disease that has killed hundreds
of millions of people and even changed the course of
history. The progress of several African battles and the
building of the Panama Canal were altered by outbreaks
of malaria. Even with the introduction of drugs for the
treatment of this disease, it remains endemic in many
BOX 12.1
Drug therapy across the lifespan
Antiprotozoal agents
CHILDREN
Children are very sensitive to the effects of most
antiprotozoal drugs, and more severe reactions can be
expected when these drugs are used in children.
Many of these drugs do not have proven safety and
efficacy in children, and extreme caution should be used.
The dangers of infection resulting from travel to areas
endemic with many of these diseases are often much more
severe than the potential risks associated with cautious
use of these drugs.
If a child needs to travel to an area with endemic
protozoal infections, the CDC or local health department
should be consulted about the safest possible preventative
measures.
ADULTS
Adults should be well advised about the need for
prophylaxis against various protozoal infections and the
need for immediate treatment if the disease is contracted.
It is very helpful to mark calendars as reminders of the
days before, during and after exposure on which the drugs
should be taken.
PREGNANCY AND BREASTFEEDING
Pregnant and breastfeeding women should not use these
drugs unless the benefit clearly outweighs the potential
risk to the fetus or neonate. Women of childbearing age
should be advised to use barrier contraceptives if any of
these drugs are used. A pregnant woman travelling to an
area endemic with protozoal infections should be advised
of the serious risks to the fetus associated with both
preventive therapy and treatment of acute attacks, as well
as the risks associated with contracting the disease.
OLDER ADULTS
Older people may be more susceptible to the adverse
effects associated with these drugs.They should be
monitored closely.
People with hepatic dysfunction are at increased risk
for worsening hepatic problems and toxic effects of many
of these drugs. If hepatic dysfunction is expected (extreme
age, alcohol abuse, use of other hepatotoxic drugs), the
dose may need to be lowered and the person monitored
more frequently.
