 However, amprenavir was withdrawn from the market in 2004 since fosamprenavir, its prodrug, proved superior in many aspects.Lopinavir was marketed in 2000 and was originally designed to diminish the interactions of the inhibitor with Val82 of the HIV-1 protease, a residue that is often mutated in the drug resistant strains of the virus.It is a peptidomimetic HIV protease inhbitor and its core is identical to that of ritonavir.