Pill giant suffering sales losses.
Glaxo said generic versions of Wellbutrin SR and Paxil IR had cost it over pounds 1.2bn in lost sales in the first nine months of its financial year.
The group, which has a plant at Barnard Castle, County Durham, said total sales of Wellbutrin products fell 30pc to pounds 173m, which was partially offset by an exceptionally strong performance by Wellbutrin XL, while sales of Paxil dropped 51pc to pounds 246m.
However, chief executive Jean-Pierre Garnier said the quarterly results, which showed total turnover flat at just over pounds 5bn, confirmed the group's success in absorbing the "significant impact" of the generic competition to the two drugs.
He added that GSK's broad portfolio of 14 products was continuing to drive performance, with sales of more than pounds 100m in the quarter.
"As the impact from Paxil generics now diminishes, we look forward to improved earnings growth in the fourth quarter and in 2005," he said.
Glaxo said the strong performance of key product growth drivers, including diabetes drug Avandia and asthma treatment Advair, were helping to keep overall sales level.
Seretide/Advair is now the world's fifth largest-selling pharmaceutical product.
Several key product launches are expected in the next six months.