The scientific rationale for the use of this combination is to inhibit the ability of the parasite to synthesise isoprenoids, as precursors of many essential compounds including sterols, carotenoids and ubiquinones. This is effected through blockade of the non-mevalonate pathway by fosmidomycin as a potent inhibitor of 1-deoxy-D-xylulose 5-phosphate reductoisomerase coupled with targeting of protein biosynthesis by azithromycin through binding to the 50S ribosomal subunit. This mode of action contrasts with the ability of the human host to utilise the mevalonate pathway for isoprenoid synthesis and accounts for the safety profiles of both drugs through the mechanism of selective toxicity. Moreover it affords protection against cross resistance with existing chemotherapeutic agents.