GlaxoSmithKline and XenoPort have settled their dispute over Horizant in a move that will see the UK major return the rights to the restless legs syndrome drug.

The companies have terminated their collaboration on Horizant (gabapentin enacarbil) extended-release tablets, though GSK will continue to sell the drug up to April next year. The decision "is aligned with GSK's ongoing strategy to streamline its portfolio to focus on core franchise opportunities", the firm says, noting that the agreement "also resolves all litigation between the parties".

That litigation stemmed from claims by XenoPort that GSK had not being doing enough to market Horizant and had materially breached its contractual duties "to use commercially reasonable efforts to maximise the sales". GSK vehemently disagreed and sued XenoPort which also filed its own complaint.

Now the matter has been settled away from the courts and XenoPort now "acknowledges that GSK fulfilled its contractual obligations on the development, manufacturing and commercialisation of Horizant". GSK has also agreed to purchase $20 million of common stock in XenoPort at a 12.5% premium to the 10-day average stock price prior to October 31 and the latter also has the option whereby GSK would buy an additional $20 million in equity.

GSK wrote off £103 million in the third quarter with respect to the RLS drug which has failed to make an impact in the market and says that no further one-off charges related to Horizant are expected.