The effectiveness of chemoprophylaxis against malaria for non-immune migrant workers in eastern Thailand.

A randomized, double-blind field trial was carried out to compare the effectiveness of mefloquine plus sulfadoxine-pyrimethamine (MSP) with that of sulfadoxine-pyrimethamine (SP) in chemoprophylaxis against malaria. The study was conducted in 193 migrant workers in the eastern rural areas of Thailand which are known to be highly endemic for multidrug-resistant Plasmodium falciparum infection. MSP was found to be more effective than SP in the suppression of both P. falciparum and P. vivax parasitaemias, when administered weekly for 12 weeks (P = 0.0014). Complete suppression of P. falciparum was achieved by MSP while 8 subjects receiving SP developed parasitaemia. One subject in the MSP group developed P. vivax parasitaemia, compared with 4 in the SP group. However, in view of the reported complications associated with the use of long-acting sulphonamides, some of which can be life threatening, prophylactic regimens containing sulfadoxine, though proved efficacious, must be used with extreme caution.