Amgen and Belgian partner UCB have abandoned efforts to develop romosozumab for fracture healing, although trials in post-menopausal osteoporosis will continue.

The two companies said they took the decision because of the high regulatory hurdles in place for fracture-healing drugs as well as the efficacy of the profile of romosozumab (also known as AMG 785) in Phase II.

Regulators have indicated they will need two long-term pivotal trials in each fracture type to consider approval, and given that the market for fracture healing is smaller than osteoporosis Amgen and UCB appear to have baulked at the level of investment required.

Furthermore, preliminary Phase II data reportedly suggest that romosozumab missed the objective of improving the time to healing of fractures - as measured by radiography - compared to placebo. The phase II programmed examined three doses of romosozumab in adult patients who suffered hip or tibial fractures treated with a surgical pin. So far only data from the tibial fracture study is available.

Amgen and UCB stressed that the safety profile of romosozumab is consistent with that seen in studies involving post-menopausal osteoporosis patients and is not a factor in the decision to drop the fracture healing indication.

Romosozumab is a humanised anti-sclerostin antibody that has already been advanced into Phase III testing in osteoporosis after encouraging results in Phase II studies were presented at the American Society for Bone and Mineral Research (ASBMR) last year.

Amgen's executive vice president of R&D said last year that the Phase II data indicate that romosozumab "produced the most impressive increase in bone mineral density over time of any agent ever introduced into clinical testing." First data from the Phase III programme are due in 2015.

"Our sclerostin antibody project with Amgen is one of the most innovative pipeline programs in UCB's portfolio," commented Iris Loew-Friedrich, the Belgian firm's chief medical officer.

"At UCB, we strive constantly to allocate our funds and resources to the most promising activities for our pipeline projects," she added.