Endo Pharma has originally signed the deal in February 2009, under which Grunenthal has given axomadol development and marketing rights Endo in the US and Canada.
The results from a Phase 2 trial evaluating axomadol showed axomadol did not meet predetermined study end points against placebo in the treatment of patients with moderate to severe chronic low back pain.
Endo Pharma R&D executive vice president Ivan Gergel said they have appreciated the opportunity to collaborate with Grunenthal on the program and they have been an excellent partner.