 Fosamprenavir is a PI that is used to treat HIV-infection in combination with ritonavir. Once hydrolyzed to amprenavir, this substance is a substrate for CYP3A4. Ritonavir is an extremely potent inhibitor of CYP3A4 and serves as a booster of the pharmacokinetics of amprenavir. Posaconazole is a very potent CYP3A4 inhibitor and therefore might enhance amprenavir pharmacokinetics in a similar way as ritonavir. 