McKenna's Pharmacology for Nursing, 2e

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P A R T 2  Chemotherapeutic agents

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 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. BOX 12.1

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 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.

Drug therapy across the lifespan