Pfizer has suffered another clinical setback and suspended trials of its investigational pain drug tanezumab, responding to concerns expressed by regulators in the USA.

The company says the worldwide suspension of the osteoarthritis clinical programme for the tanezumab follows a request by the US Food and Drug Administration. The clinical hold, which is effective immediately, follows “a small number of reports” of tanezumab patients experiencing the worsening of OA leading to joint replacement and Pfizer noted that to date, “this adverse event has not been observed in non-OA patient populations”.

The FDA has asked that, later this week, Pfizer present its assessment of “the potential implications of the adverse events in the OA programme” for the other non-OA tanezumab trials. These include studies in patients with cancer pain, interstitial cystitis, chronic low back pain and painful diabetic peripheral neuropathy.

The company says it is actively working with the FDA “to determine the appropriate course of action”. The suspension comes less than a week after Pfizer presented positive late-stage data on tanezumab at the European League Against Rheumatism meeting in Rome.

The Phase III trial involved 690 patients who suffered from chronic knee pain from OA but were either unable to take an non-steroidal anti-inflammatory drug or Pfizer’s own COX-2 inhibitor Celebrex (celecoxib). Patients in all three dose groups - 2.5mg, 5mg and 10mg - reported a statistically significant reduction in pain compared with placebo and the patients also demonstrated a significant improvement in physical function.