Fosamprenavir (marketed by ViiV Healthcare as fosamprenavir calcium), under the trade names Lexiva (U.S.) and Telzir (Europe) is a pro-drug of the protease inhibitor and antiretroviral drugamprenavir. The FDA approved it October 20, 2003, while the EMEA approved it on July 12, 2004. The human body metabolizes fosamprenavir in order to form amprenavir, which is the active ingredient. That metabolization increases the duration that amprenavir is available, making fosamprenavir a slow-release version of amprenavir and thus reducing the number of pills required versus standard amprenavir.
A head-to-head study with lopinavir showed the two drugs to have comparable potency, but patients on fosamprenavir tended to have a higher serum cholesterol. Fosamprenavir's main advantage over lopinavir is that it is cheaper.
^Eron J Jr, Yeni P, Gathe J Jr, et al. (2006). "The KLEAN study of fosamprenavir-ritonavir versus lopinavir-ritonavir, each in combination with abacavir-lamivudine, for initial treatment of HIV infection over 48 weeks: a randomised non-inferiority trial". Lancet368 (9534): 476–82. doi:10.1016/S0140-6736(06)69155-1. PMID16890834.