[Failure of prevention of malaria by mefloquine in West Africa].

Mefloquine (Lariam) is extensively prescribed for the prevention of malaria in chloroquine-resistant areas. However, in west Africa, most of the strains of Plasmodium falciparum are still sensitive to chloroquine. In addition, a few of these strains are inherently resistant to mefloquine. Under these conditions, we must expect to see the failure of mefloquine prophylaxis in travellers returning from west Africa. We report here 5 such failures. The in vitro susceptibility of Plasmodium falciparum isolates from 4 of these patients was evaluated and showed that all 4 had normal sensitivity to chloroquine and quinine, 3 were resistant to mefloquine and one had reduced susceptibility to mefloquine. Mefloquine blood levels (measured 3 times) were within the normal protective range. These case reports indicate that mefloquine should be used cautiously for malaria prevention in west Africa. They also point out that, regardless of the prophylactic method used, fever in a traveller returning from endemic malaria regions always dictates the analysis of a thick blood smear to rule out the diagnosis of malaria.