GlaxoSmithKline has announced to close its manufacturing site in Dartford, UK, which will result in the loss of 620 jobs.

The job cuts will take place over the next four years and the plant is to close in 2013, GSK said, noting that production will be transferred to alternative facilities. The closure is subject to consultation with trade union and staff representatives, the firm added.

There has been “a substantial decline in forecast demand for the Dartford site’s two largest products which, prior to patent expiries, account for 60% of total volumes manufactured at the site”, GSK noted. It was referring to Lamictal (lamotrigine) for epilepsy and bipolar disorder and Valtrex (valaciclovir) for herpes.

Both have been big earners for the firm but Lamictal has faced generic competition since July, while Valtrex is expected to suffer a similar fate at the end of next year. GSK added that “the current level of manufacturing activity at Dartford is not expected to be replaced by the same level of new business, driving utilisation at the site down to an unsustainable level”.

Joe Foley, site director, said GSK “regrets the impacts this proposal would have on employees and the local community, with whom we have built strong links over many years”. He added that the proposal is “no reflection on the professionalism and commitment of Dartford employees, but that of the fiercely competitive environment in which the pharmaceutical industry operates”.

The announcement comes a week after GSK said it is reducing its US sales force by around 1,000 to 7,500.