The resistance of P. falciparum to chloroquine is nearly universal; chloroquine remains effective only in Mexico, areas of Central America that are west of the Panama Canal, the Caribbean, East Asia, and a few Middle Eastern countries. In all other areas where malaria is endemic, atovaquone–proguanil, mefloquine, or doxycycline is recommended by the CDC and WHO. Primary prophylaxis with chloroquine when appropriate and a choice of atovaquone–proguanil, mefloquine, or doxycycline for other areas according to traveler circumstances is recommended by these organizations.
New England Journal of Medicine - Vol. 359, No. 6, August 7, 2008