Warner Chilcott has been boosted by victory in a US patent case that analysts believed could threaten up to 15 per cent of its earnings.

The Craigavon-based firm, previously called Galen, said yesterday that the patent on its anti-depressant drug, Sarafem, had been upheld.

The case considering the matter had spanned some 19 months.

It hinged on the patent expiration date for Sarafem, which Warner Chilcott bought from Eli Lilly at the end of 2002 for €292.5 million.

A US firm, Teva Pharmaceuticals, tried to copy the drug and begin selling a generic version but Warner Chilcott argued that this was illegal under Sarafem's patent.

A judge in the US District Court for the Southern District of Indiana this week sided with Warner Chilcott.

As a result, Sarafem can not be copied until May 2008 at the earliest.

Warner Chilcott chief executive, Mr Roger Boissoneault, said last night that he was "extremely pleased" with the outcome.

"Sarafem is, and will continue to be, an important product for us," he added.

Shares in Warner Chilcott fell sharply last week, partly due to nervousness about the outcome of the court case and partly over concerns that Sarafem could carry unwanted side-effects.

The drug is used in the treatment of pre-menstrual disorder, but was rumoured to have some fertility-enhancing effects. This was definitively dismissed by Warner Chilcott.

Shares in the firm closed down 5p at 600p in London last night, with news of the legal win emerging after the market closed.

It was unclear yesterday whether Warner Chilcott would have to pay its own expenses in the case. The firm estimated last year that it could cost up to $2 million (€1.7 million).