Shire has filed a complaint alleging that Allergan is blocking competition in the dry eye therapy area. The common condition, which can cause vision loss, is a lucrative market.

Shire’s Xiidra (lifitegrast), launched in the US last year, and Allergan’s veteran blockbuster Restasis (cyclosporine), are key players in this space.

But in a filing at New Jersey District Court, Shire alleges that Allergan is in effect blocking competition in Medicare drug plans.

Reuters reports that Shire says: “Allergan has, and will continue to use, bundled discounts, exclusive dealing, coercion and interference to unlawfully ‘block’ Shire from competing with it, and to maintain its monopoly in the Part D market at all costs.”

According to the news agency, an Allergan spokesman dismissed this claim, saying: “Competition in the chronic dry eye therapeutic market has driven pricing down for patients and payers in Medicare Part D and commercial plans. Restasis continues to provide significant value to Medicare beneficiaries, providers and the Part D programme.”

For Allergan, Restatis is a valuable commodity, second only to Botox in terms of revenue. In a complex deal last month, the company transferred some patents for the product to the Saint Regis Mohawk Tribe.

The tribe, which is recognised as a sovereign tribal government, is attempting to diversify its business interests. It will receive $13.75 million upon execution of the agreement and is eligible to receive $15 million in annual royalties.

The unusual agreement is seen as a way for Allergan to head off challenges to its intellectual property from generics manufacturers. As a designated sovereign entity, the tribe has protection from patent challenges.

The dry eye market is a target for several manufacturers. Earlier this year, Novartis exercised an option to in-license experimental eye drug ECF843 from US biopharma Lubris.

The move gives the Swiss drug giant worldwide rights outside Europe to the drug for ophthalmic indications, focusing on dry eye.