Indivior Inc. on Tuesday sued to block a rival drugmaker from bringing a generic version of an under-the-tongue form of Suboxone to market, after being dealt a stinging loss last month in an ongoing effort to protect its top-selling drug.

In a seven-page complaint, filed in the U.S. District Court for the District of Delaware, U.K.-based Indivior said Teva Pharmaceuticals’ subsidiary Actavis Laboratories had infringed the so-called ’305 patent for the opioid-addiction treatment with applications to develop and sell a copycat of the drug in the United States.