DRUGS company GlaxoSmithKline is hoping that its string of top-selling products will be able to fight off competition from copycat versions.

Leading the charge will be the firm's answer to impotence drug Viagra.

The group beat City expectations yesterday, revealing that its underlying pre-tax profits had soared 22 per cent to £1.69bn in the third quarter - equivalent to just under £218 a second.

Turnover was up nine per cent to £5.47bn in the three-month period.

But Glaxo warned that the launch of a generic rival to its anti-depressant Paxil in the US was likely hit sales in the final quarter of the year.

Sales of Paxil were up by ten per cent in the quarter to £542m, but the generic rival had a limited impact on sales for the quarter as it was launched late in the period.

Glaxo hopes to plug the gap with a range of leading drugs such as Seretide, an asthma treatment, and anti-diabetes product Avandia.

It also launched two drugs in the US during the quarter - Levitra for erectile dysfunction and depression treatment Wellbutrin XL.

The company revealed that Levitra had already attracted 12 per cent of new prescriptions for the condition in the US after only six weeks on the market.

Chief executive Jean-Pierre Garnier said: "The continued strong growth of our key products, such as Avandia, and the successful US launches of Wellbutrin and Levitra, clearly demonstrate the commercial strength of our business."