THE UK's biggest pharmaceuticals firm, GlaxoSmithKline, faces a cut-price assault on its second biggest selling drug.

For the first time Paxil, until this year GSK's top seller, faces the threat of a generic copy.

The onslaught was expected, but the launch of a rival copycat antidepressant came several months earlier than many in the industry thought.

Paxil had US sales of £1.41bn last year, a figure which will be hit by the newcomer from Canadian drugs firm Apotex.

It is a blow for GSK, which invested heavily in research and development of the treatment.

But the impact of a generic version will be lessened by steps taken by GSK, which employs 1,100 people at a plant in Barnard Castle, County Durham.

Last year it launched a longer-lasting version of Paxil, called Paxil CR, which has fewer side effects.

GSK has revealed in July that it is making profits of £242 every second and saw half-year profits soar 16 per cent to £3.55bn.