DHFR and malaria: When used as first line treatment for malaria, SP exerts a strong selection pressure on parasite populations, thus increasing the frequency of resistance mutations in the dihydrofolate reductase (dhfr) gene which codes for the enzyme DHFR (the target of pyrimethamine) [2,3] and the dihydropteroate synthase (dhps) gene which codes for the enzyme DHPS (the target of sulphadoxine) [4,5] in the parasite reservoir [6].