Sanofi has handed back rights to the inhaled insulin treatment Afrezza to US drug development company MannKind.

Sales of Afrezza, which launched in the US in February last year, have been disappointing. A Sanofi spokesman told the news agency Reuters that the product never met even modest expectations while costs were projected to remain very high for a significant period.

MannKind said the companies would promptly start discussions to secure a “smooth and orderly transition in the development and commercialization of Afrezza from Sanofi over the next 90-180 days.”

In any event, termination of the license agreement would be effective no later than six months from the date of Sanofi’s notice, or Jul. 4, 2016.

The company added that it was reviewing its strategic options for Afrezza. Industry observers believe that MannKind could face bankruptcy as a result of Sanofi’s decision.