Menlo Park, Calif.-based Corcept Therapeutics Inc. said it will "vigorously defend" the validity of a patent covering its drug Korlym against Neptune Generics LLC.

Neptune Generics submitted an inter partes review petition on Aug. 2 at the U.S. Patent Trial and Appeal Board challenging U.S. Patent No. 8,921,348 which is related to Korlym — used for controlling hyperglycemia, or high blood sugar levels, in patients suffering from Cushing's syndrome, a rare, debilitating endocrine disorder.

The patent board has not given a filing date to the petition.

Corcept noted that Neptune does not have regulatory approval to sell any drug in the U.S.

Neptune, a specialty and generic pharmaceutical company, is backed by Burford Capital Ltd., a U.K.-based legal finance company.