Dec 29 (Reuters) -

A U.S. judge on Friday ruled against Corcept Therapeutics in a patent infringement lawsuit the pharmaceutical firm had brought against Teva Pharmaceutical, sparking a frenzied stock sell-off.

Shares of Corcept fell 38% in trading after the bell.

The company had failed to demonstrate a likelihood of direct infringement of its patent by Teva, a United States district judge ruled.

Teva has been selling a generic version of Corcept's Korlym (mifepristone) drug, which is used to treat Cushing’s Syndrome.

"Corcept failed to introduce credible record evidence that

anyone has ever previously infringed the asserted claims," the ruling stated. (Reporting by Niket Nishant in Bengaluru; Editing by Shounak Dasgupta and Pooja Desai)