Fosamprenavir calcium (Lexiva®) is a pro-drug of the protease inhibitor and antiretroviral drugamprenavir. The FDA approved it October 20, 2003. 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 prodrug is a pharmacological substance (drug) which is administered in an inactive (or significantly less active) form. ... Protease inhibitors are a class of medication used to treat or prevent viral infections. ... Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. Different classes of antiretroviral drugs act at different stages of the HIV life cycle. ... Amprenavir (Agenerase®) is a protease inhibitor used to treat HIV. It was approved by the FDA on April 15, 1999, for twice-a-day dosing instead of needing to be taken every eight hours. ... October 20 is the 293rd day of the year (294th in leap years) in the Gregorian Calendar, with 72 days remaining. ... 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ...