GSK pips Pfizer to the post in introducing its erectile dysfunction drug into the US market

The biggest drugmaker in the UK, GlaxoSmithKline, has won approval to sell its new impotence pill in the US setting the scene for a giant battle against Pfizer's Viagra.

Levitra was cleared by the US regulator, the Food & Drug Administration, and will be available within days. The news gives Levitra a crucial head start against Eli Lilly's Cialis, which is also set to challenge Viagra but whose approval has been stalled.

GSK says that 30 million men in the US alone suffer from some form of impotence, with only a fraction seeking treatment. Analysts believe global sales of erectile dysfunction drugs could total £3bn a year by the middle of the decade, with the US being by far the largest market.

GSK will market Levitra with Bayer, the German drugs giant which originally developed the drug.

Chris Viehbacher, president of US pharmaceuticals at GSK, said: "Together with Bayer, we are committed to educating men and their doctors about Levitra and the important role it can play to improve their sexual health."

Like Viagra, Levitra acts by blocking an enzyme that limits blood flow to the penis during arousal. GSK is attempting to differentiate the drug by saying it works more quickly than Viagra and does not have the side effect of turning some people's vision blurry or blue.

Pfizer is trying to counter the launch of the new rivals with a US marketing campaign for Viagra fronted by the footballer Pele. It has also launched legal action claiming Levitra and Cialis infringe its patents - a tactic which has already failed in Europe.

Kevin Scotcher, analyst at SG Cowen, said Levitra's approval had come earlier than expected, giving it an estimated three month head start over Cialis, which had been first to market in Europe.

But Cialis has made headway in the battle of brand awareness where it has been launched, and in France is already being dubbed "le weekend" because studies suggest it can be taken on a Friday and its effects may still be felt on Sunday morning.

He said: "Lilly has been eager to limit the impact of the early Levitra launch in the US by pointing out that in European markets where it is available - Germany, France, the UK and Italy - Cialis has greater market shares than Levitra. We expect Levitra to generate around $1bn (£627.7m) of worldwide sales by 2007."

Levitra is likely to be priced at a discount to Viagra and be backed by a marketing campaign costing around $100m in the first year. GSK is sponsoring the National Football League in the US and has signed up the former Chicago Bears coach Mike Dikta to promote awareness of erectile dysfunction.