Malaria prophylaxis is relative, not absolute, but can provide much protection. Travellers must take prophylactics regularly while in malarious areas and for one month thereafter; despite doing so, they may still develop malaria. For areas without chloroquine-resistant malaria, chloroquine, 300 mg base weekly, or proguanil, 100-200 mg daily, are preferred. In areas of chloroquine sensitivity there may be places with resistance to proguanil and pyrimethamine, but these places are not delineated. The risk of breakthrough of malaria is, therefore, least with chloroquine, but problems of potential side effects and regular medication are fewer with proguanil than chloroquine. Proguanil is preferred for long-term prophylaxis. Malaria poses a greater hazard for pregnant women and infants than do prophylactics. Pyrimethamine/sulphadoxine (Fansidar) or pyrimethamine/diaminodiphenyl sulphone (maloprim) are the preferred drugs for areas with prevalent chloroquine-resistant plasmodium falciparum. Fansidar is taken once a week and Maloprim also is usually recommended to be taken once a week.