The US Food and Drug Administration has placed on hold a Phase IIb study assessing Teva and Regeneron's investigational nerve growth factor inhibitor fasinumab for chronic low back pain.

The move was spurred by the emergence of a case of adjudicated arthropathy (joint disease) in a patient receiving high dose fasinumab who had advanced osteoarthritis at study entry.

Regeneron has completed an unplanned interim review of results and has stopped dosing in the study. This found "clear evidence" of efficacy with improvement in pain scores in all fasinumab groups compared to placebo, and preliminary safety results were generally consistent with previous findings.

Based on these data, the firms say they plan to design a pivotal Phase III study in chronic low back pain that excludes patients with advanced osteoarthritis.

"We are making data-driven decisions on Phase III fasinumab dosing that we believe will maximise potential benefit for patients in need, while minimising the likelihood of side effects," said George Yancopoulos, Regeneron's chief scientific officer.

"We believe fasinumab represents an important potential innovation for patients with osteoarthritis pain and chronic low back pain who currently have clear unmet need and limited treatment options," added Michael Hayden, president of Global R&D and chief scientific officer at Teva.

However, Geoffrey Porges at Leerink has basically written off the drug. "Based on this hold, and the history of the class, we are reducing our probability of success to zero, and removing all fasinumab revenue (and future milestones) from our model and REGN valuation", reports Endpoints News.