LONDON – GlaxoSmithKline Plc has signed a deal potentially worth up to $820 million with Valeant Pharmaceuticals International to access the U.S. company's experimental epilepsy and pain treatments.

The alliance gives Europe's biggest drugmaker worldwide rights to a new epilepsy drug, retigabine, that could reach the market in 2010.

The move is the latest in a slew of deals clinched by Glaxo with smaller partners, designed to boost its pipeline of experimental medicines.

Valeant will get an upfront payment of $125 million for granting Glaxo development and commercialisation rights to retigabine, which has already completed Phase III trials in patients with difficult-to-treat epilepsy.

Valeant and Glaxo plan to submit the drug for regulatory approval in the United States and Europe by early 2009.

Retigabine is also being tested in patients with post-herpetic neuralgia, a painful and common complication of shingles.

In addition, Glaxo will pay Valeant up to $545 million based on the achievement of certain regulatory, development and commercialisation milestones and the development of additional indications for retigabine.

Valeant will share up to 50 percent of net profits within the United States, Canada, Australia, New Zealand and Puerto Rico, and will receive up to a 20 percent royalty on sales elsewhere.

The U.S. group could also receive up to a further $150 million, depending on progress of VRX698 and other back-up compounds within the same potassium channel opener discovery programme.

Steve Stefano, head of Glaxo's U.S. NeuroHealth Division, said the Valeant deal was an attractive commercial proposition given the significant need for novel anti-epileptic drugs.

“Almost one-third of patients with epilepsy continue to experience seizures despite treatment with currently available medications,” he said.

“We believe that retigabine could potentially play a significant role in improving the management of epilepsy.

(Reporting by Ben Hirschler; Editing by Jason Neely)