Fosamprenavir, a Vertex Pharmaceuticals phosphate ester prodrug of the HIV protease inhibitor amprenavir, is under development by GlaxoSmithKline (GSK; formerly Glaxo Wellcome) for the potential treatment of HIV infection in adults and children. By November 2000, it was in phase III trials; a third phase III trial was initiated in April 2001. In October 2001, GSK expected filing in both the EU and US in 2002. In January 2002, Vertex anticipated an NDA filing during the second half of 2002. Fast-track status for fosamprenavir was received by Glaxo Wellcome in December 1999. As of January 2002, enrollment was complete for two of the three phase III trials, and an NDA was expected to be filed during 2002. Fosamprenavir was first synthesized at Vertex as part of a collaboration with Glaxo Wellcome and by 1999, it was being developed by Glaxo Wellcome as part of an ongoing agreement between the two companies. In September 2000 and January 2001, Merrill Lynch predicted a 2002 launch, with sales of pounds sterling 50 million in 2002, rising to pounds sterling 150 million in 2004.