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Stryker's OP-1 Putty Not Approvable According to FDA Panel BY ARIELLA P. GOLOMB, MD, APRIL 1, 2009

Yesterday an FDA advisory panel voted 6-1 that Stryker's PMA for its OP-1 Putty for uninstrumented posterolateral fusion for the treatment of lumbar spondylolisthesis was "not approvable." Stryker was seeking this approval based on 24 months of clinical outcome data and 36 month CT scan and reoperation rates. The CT scan and reoperation data was gathered via an extension study to the company's original PMA.

There was a general consensus going into the meeting that the trial results made the likelihood of OP-1's approval very low. Stryker has been struggling with the product's approval since submitting the PMA application to the FDA back in 2006, at which point the clinical data was not supportive of product approval and the FDA required additional studies.

The FDA panel cited numerous issues with the data presented, including:

  • The study results presented by Stryker were based on post-hoc analysis, a "flag" the group could not get past. In addition, the panelists cited biases within the study design as well as the introduction of type I errors (false positives).
  • The clinicians argued that the presence of bone is not equivalent to bridging bone and the stabilization seen could have resulted from fibrous tissue formation.
  • The patients selected for the study were a "stiff" patient population to start.
  • There are unanswered questions related to immunologic effects of the protein.

Among the speakers in support of OP-1's approval was Dr. David Wong, who highlighted that OP-1 fulfills an unmet clinical need. There is currently no other approved product for posterolateral lumbar fusions, and the product will spare patients from iliac bone graft harvesting. Dr. Wong also pointed out the large amount of post-marketing data available on the product (used in over 15,000 cases under a Humanitarian Device Exemption) and an average of 4.4 years of follow-up data was maintained. To address immunologic safety concerns, Stryker pointed out that 5-10% of humans have preexisting anti-BMP antibodies and there was no difference in adverse events seen between patients with neutralizing antibodies and those without. The panel complimented Stryker for the "honest design" of the study (no instrumentation or ceramics that could obfuscate radiographic interpretations) and executing on the clinical study when state-of-the-art care is constantly changing.

Dr. Paul McCormick, the lone hold out in the vote, said that even though the efficacy had not been proven and he would recommend approval only with significant conditions, the product was effective in some patients, was able to create bone and would have served as another "tool" in his surgical practice. This statement highlights the appetite among the clinical community for more orthobiologic solutions.

Yesterday's panel results were not the only recent setback for the OP-1 franchise. OP-1 is currently marketed under a Humanitarian Device Exemption (HDE) and the company is currently facing a federal grand jury investigation over the marketing of OP-1.

At this point, an approval for OP-1 in posterolateral lumbar fusion would most likely require Stryker to start over with a new clinical trial. Of note, the immunogenic effects of the protein were not observed when injected into the immune-privileged intervertebral discs in rabbits. This would support an investment in additional OP-1 product development for an indication for Degenerative Disc Disease.

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