Akorn Inc. said Monday it has filed a complaint against Fresenius SE & Co. in a Delaware court, asking that Germany-based Fresenius be required to fulfill its obligations to complete its buyout agreement. Earlier, Fresenius said it was ending the deal to buy the generic drug maker, following an investigation into possible violations of Food and Drug Administration data-integrity requirements, which Akorn responded by saying it "categorically" disagreed with the decision. In the filing with the Delaware court, Akorn said the attempt to end the merger is a breach of the agreement without merit. "The investigation is not a condition to closing and the only remaining condition is approval from the Federal Trade Commission," the company said in the filing. "We intend to vigorously enforce our rights, and Fresenius' obligations, under our binding merger agreement." Akorn's stock tumbled 33% in premarket trade. It has shed 40.6% over the past three months, while the S&P 500 has lost 6.0%.