There is ample evidence documenting the increasing incidence of malaria worldwide, due in large part to the spread of Plasmodium falciparum. The deteriorating efficacy of existing antimalarial drugs, because of increasing numbers of drug-resistant parasite strains, makes routine prophylaxis and treatment of the disease a therapeutic challenge.
Deciding which drug to use depends on a number of factors, including the patient's age and his or her clinical and immune status. Other important considerations are the type of malaria (vivax, falciparum, ovale, or malariae), outcome desired, drug availability and costs, side effects and degree of compliance expected with the prescribed regimen, drug sensitivity of the parasite strain in the area in which the infection was acquired, and the most appropriate route of administration.
Antimalarial drugs are used for five basic purposes (Webster, 1990): to prevent infection from establishing itself in the body (causal prophylaxis); to prevent an established infection from manifesting itself clinically (suppressive prophylaxis); to treat an acute attack of malaria in order to relieve symptoms, eliminate asexual stages of the parasite, or completely eliminate malaria parasites from the body (treatment therapy); to eliminate parasites, whether or not they are causing symptoms (curative therapy); and to eliminate persisting liver forms of the parasite (antirelapse treatment). A sixth use of antimalarial drugs, not now employed, relies on mass distribution of compounds that eliminate gametocytes in infected individuals to reduce parasite transmission in human populations.
Since causal prophylactic agents are few, logistically difficult to administer (daily doses are required), and often toxic, this approach to preventing malaria is seldom practical. Additionally, there is parasite resistance to one of the major causal prophylactics, pyrimethamine. Most prophylactic drugs suppress parasitemia and clinical disease. Antirelapse or radical curative treatment may be given either after clinical treatment of a relapsing malaria (caused by P. vivax or P. ovale) or following suppressive prophylaxis when exposure to either of these parasites has occurred.
The goals of treating an established infection can also vary. In people who have no natural immunity and are only temporarily exposed to the parasite (e.g., migrants, travelers, military personnel, and temporary laborers), infections must be treated vigorously to eliminate all malaria parasites from the body, since parasitemia may reach life-threatening levels in a short period of time. Children up to the age of four living in endemic regions are at serious risk of severe and even fatal infection. Prompt treat-