Pfizer has filed a lawsuit against Japan’s Dainippon Sumitomo Pharma in a UK court to try to end a licensing agreement for the blood pressure drug Amlodin.

Pfizer is calling on Dainippon Sumitomo to return all data on Amlodin (amlodipine besylate) and brings production and marketing of the product by the Japanese firm to a halt, on the grounds that the licensing agreement is no longer valid.

The US drugmaker says former licensee Sumitomo voided its right to Amlodin following its merger with Dainippon last October. Last November, faced with Pfizer’s demands, Dainippon Sumitomo filed a lawsuit in Tokyo to try to force an acknowledgement of the validity of the licensing arrangement.

Dainippon Sumitomo and its parent Sumitomo Chemical insist that the UK court has no jurisdiction on the matter and, whatever its verdict, the licensing agreement would still remain in force.

Amlodin is Dainippon Sumitomo's biggest-selling product, pulling in almost $500 million annually.