Efficacy of drug prophylaxis.

With the spread of chloroquine resistant Plasmodium falciparum the control of malaria has become increasingly complex. In recent years, particular concern has arisen over how best to prevent malaria in non-immune international travellers. Prior to the recognition of the potential toxicity of some antimalarial drugs, malaria preventive guidelines switched from chloroquine to the newer compound antimalarial drugs and to amodiaquine; this adjustment was made when sentinel cases alerted clinicians that breakthrough infections occurred in travellers to East Africa taking chloroquine prophylaxis. Changes were also supported by data derived from field studies illustrating the effectiveness of these drugs for therapy in indigenous populations. However, international studies have now documented serious adverse reactions to pyrimethamine/dapsone, pyrimethamine/sulphadoxine, and amodiaquine, and caution is required with their use. Rates in British users concur with international estimates. Specialists preparing malaria preventive guidelines have, therefore, preferred to recommend the use of relatively safe antimalarial drugs, like chloroquine and proguanil, provided they offer non-immune travellers adequate protection against P. falciparum infections. Substantial difficulty has arisen, however, in the definition of 'adequate protection'. Field studies in indigenous communities with partial immunity can provide concise biological measures of parasite resistance to drugs. Unfortunately, these data cannot be used directly to determine the expected efficacy of chemoprophylactic drugs in non-immune populations. The transmission of malaria and the degree and intensity of resistance vary even within small geographical areas. Comprehensive patterns of resistance cannot be mapped out on a countrywide or regional basis for logistic reasons, and are restricted focally to discrete study locations.(ABSTRACT TRUNCATED AT 250 WORDS)