Dealers say the move takes it head-to-head with US rival Pfizer's Viagra in its own backyard. They fear GSK will have its work cut out making inroads into Viagra's dominant position. In addition, Eli Lilly-Icos launches impotence treatment Cialis later this year. Brokers say the Levitra news is already reflected in the share price. Rival AstraZeneca, which last week won FDA approval for its fatbusting drug Crestor, fell 68p to 2502p. It faces tough competition in the US, a market thought to be worth $20bn (£12.6bn) a year. Switzerland's Novartis has also launched a generic rival to AZ's ulcer treatment Losec.