16.8.3 Extracts with neither In Vitro nor In Vivo Activity

16.8.4 Phytomedicines with Several Plant Ingredients 16.9 Conclusions



For the foreseeable future, chemotherapy and impregnated bed nets will remain the two most useful tools for the control of the deadly disease malaria, which kills 2 million people each year. Paradoxically, only approximately 10 antimalarial drugs are available on the market for the prevention or the treatment of malaria, and the development of new ones is costly and time-consuming. The use of chemotherapy for controlling the pathogenic organism is further restricted by the development of drug resistance. As there is no longer a single drug that can prevent or cure all cases of malaria, researchers have reconsidered the entire therapeutic approach for the control of this old and most devastating tropical disease. A more flexible attitude should be adopted to this end. Whereas the urgent need for the discovery or design of new antimalarial drugs with different mechanisms of action is recognised, plant-based antimalarials form the basis of medicines used by the majority of people in most regions afflicted with malaria. Many have been shown in experimental studies to have antiplasmodial effects, and as such, they may offer viable alternatives to prescription drugs in the treatment of this life-threatening disease.

Before a traditional antimalarial plant can be used in primary health care, however, it is essential to adequately assess its efficacy. Indeed, insufficient evidence of the efficacy of an herbal product is not acceptable, particularly when that product may entail serious health risks. Evaluating the efficacy of antimalarial plants may be viewed at two levels. The first is to demonstrate that, in the form in which they are used in traditional medicine to treat malaria, they have beneficial effects. The second, assuming that chemically defined constituents are responsible for the observed activity, is to isolate these constituents for further investigation. Based on our own experience and our exchange of views with colleagues involved in a malaria research program, we will propose in this chapter guidelines for the preparation of extracts of plants, bioassay with crude extracts, and bioassay-guided fractionation procedures.


When dealing with traditional medicine, it is important to bear in mind that healers basically treat the symptoms of a disease, especially those that are apparent to them. As malaria can produce a wide variety of symptoms, over 1200 plant species are used to treat this disease (see Chapter 11). Medicinal plants considered effective in the treatment of malaria are therefore those observed by healers to alleviate or prevent one or more recognised symptoms of malaria. As malaria can occur concurrently with other infectious diseases, accurate diagnosis can be difficult to achieve, and this makes malaria symptoms somewhat complex. Ethnomedical beliefs of populations also play a role in the choice of plants for the treatment of malaria. Based on these considerations, antimalarial plants can be roughly divided into three categories:

1. Plants with a direct effect on the parasite, either at the erythrocytic stage (antiplasmodial drugs) or at the hepatic stage (preventive drugs)

2. Plants with effects on host-parasite relationships (immunostimulants, antipyretics, etc.)

3. Plants with no clear effects on malaria, but with probable psychosomatic action, the use of which originates from ethnomedical beliefs

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