Plasmodium species infections, drugs

Malaria parasites have a complex life cycle that permits drug action at several points. Plasmodium species that infect humans P falciparum, P malariae, P ovale, P vivax) tire spread by the female Anopheles mosquito and, after inoculation into the human host, undergo a primary developmental stage in the liver (primary tissue phase). They then enter the blood and parasitize erythrocytes (erythrocytic phase). P falciparum and P malariae have only one cycle of liver cell invasion thereafter, multiplication is confined to erythrocytes. The other species have a dormant hepatic stage (in which they become bypnozoites) that is responsible for recurrent infections and relapses after apparent recovery of the host from the initial infection. 

Quinine is a cinchona alkaloid that acts rapidly against all four species of Plasmodium. It is used to treat protozoal infections and leg cramps, and as a bitter and flavoring agent. However, the drug is not used prophylactically for malaria. Quinines are contraindicated in patients with a history of hypersensitivity to quinine or quinidine. They should not be used in the presence of hemolysis and should be used with caution in patients with atrial fibrillation, cardiac conduction defects, or heart block. Quinine administration in myasthenia gravis may aggravate the disease, hence it should be avoided. Quinine can be used in pregnancy.37 Intravenous infusion of quinine should be slow, and the patient should be monitored for cardiotoxicity.38 Cinchonism, which is characterized by tinnitus, GI disturbances, and impaired vision may occur with therapeutic doses of quinine.39... 

The effectiveness of a drug treatment is related to the particular species of infecting plasmodium and the stage of its life cycle. A summary of the life cycle of the parasite and the sites of therapeutic interventions are presented in Figure 35.4. 

Protozoal infections. Malaria is the major transmissible parasitic disease in the world. The life cycle of the plasmodium that is relevant to prophylaxis and therapy is described. Drug resistance is an increasing problem and differs with geographical location, and species of plasmodium. 

Once hailed as die king of diseases (/), malaria is one of die oldest cross-cultural infections of our time (2). The most common and deadly species of the human malaria parasite, Plasmodium falcipeach year. These statistics combined Mddi die development of drug resistant parasitic strains and vectors place a two billion dollar mmual economic burden on precisely those populations least capable of shouldering it (3-6). 

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