Fosamprenavir under the trade names Lexiva (U.S.) and Telzir (Europe) is a pro-drug of the protease inhibitor

Protease inhibitor (pharmacology)

Protease inhibitors are a class of drugs used to treat or prevent infection by viruses, including HIV and Hepatitis C. PIs prevent viral replication by inhibiting the activity of proteases, e.g.HIV-1 protease, enzymes used by the viruses to cleave nascent proteins for final assembly of new...

 and antiretroviral drug

Antiretroviral drug

Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. When several such drugs, typically three or four, are taken in combination, the approach is known as Highly Active Antiretroviral Therapy, or HAART...

 amprenavir. 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

Lopinavir

Lopinavir is an antiretroviral of the protease inhibitor class. It is used as a fixed-dose combination with another protease inhibitor, ritonavir, under the trade names Kaletra and Aluvia ....

 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. Although fosamprenavir does not itself require refrigeration, it is usually given with ritonavir

Ritonavir

Ritonavir, with trade name Norvir , is an antiretroviral drug from the protease inhibitor class used to treat HIV infection and AIDS....

which does.