RESEARCHERS HAVE found that an experimental drug against malaria is becoming ineffective. The antibiotic, fosmidomycin, blocks the synthesis of a class of molecules called isoprenoids which keeps the malaria pathogen healthy. When researchers compared the genetics of malaria parasites that responded to the drug to the genetics of malaria parasites that were resistant to it, they found mutations in a gene called PfHAD1. The PfHAD1 protein normally slows down the synthesis of isoprenoids, but in the resistant parasites the mutation resulted in higher production of isoprenoids. So, even when the antibiotic is there, it doesn't kill the cells.