New Drug Relieves Back Pain, But Safety Issues Remain

By Pat Anson, PNN Editor

An experimental non-opioid pain reliever gives long-term relief for chronic low back pain, but questions remain about joint damage and other side effects from the drug, according to a large new study.

Tanezumab is a humanized monoclonal antibody that targets nerve growth factor (NGF), a protein in the blood that heightens pain sensitivity. Tanezumab binds to NGF and inhibits pain signals from reaching the brain.

In a Phase III study of over 1,800 patients with difficult-to-treat low back pain, participants given an injection of tanezumab once every two months had significantly more pain relief than those given tramadol or a placebo. The study was funded by Pfizer and Eli Lilly, which have spent nearly a decade jointly developing tanezumab as an alternative to opioid medication.

"This demonstration of efficacy is a major breakthrough in the global search to develop non-opioid treatments for chronic pain," said lead author John Markman, MD, director of the Translational Pain Research Program at the University of Rochester Medical Center. "There were also improvements in function linked to the reduction in pain severity."

But this “major breakthrough” is tainted by the fact that about 10% of patients given 10mg of tanezumab had joint pain or other side effects. Seven of them needed total joint replacement surgery. Patients who received 5mg injections of tanezumab had fewer side effects, but less relief from back pain.

NGF inhibitors have previously been linked to a rapidly progressive form of osteoarthritis. But researchers say other methods of treating back pain, such as opioids, non-steroidal anti-inflammatory drugs (NSAIDs) and surgery, have their own safety risks.

"In the future, clinicians may have to weigh the different risks of lumbar fusion surgery, chronic opioid use, or NSAIDs against the unique risks of a rare but rapidly progressive form of joint problem associated with blocking nerve growth factor," said Markman. "I expect that that the tradeoffs between benefit and risk will be different for osteoarthritis than for chronic low back pain."

Tanezumab is currently under review by the Food and Drug Administration as a treatment for moderate-to-severe osteoarthritis (OA), with a decision expected late this year. In a 2019 study of osteoarthritis patients taking a 5mg dose of tanezumab, there was significant improvement in their pain and physical function. But about 6% experienced rapidly progressive osteoarthritis.

Pfizer and Eli Lilly are not currently pursuing tanezumab as a treatment for chronic low back pain (CLBP).  

“Pfizer and Lilly made the decision to prioritize OA based on an assessment of the totality of SC tanezumab data and an initial discussion with the FDA,” a Pfizer spokesman said in an email to PNN. “At this time, regulatory submissions are not planned for tanezumab in patients with moderate-to-severe CLBP. Additional data analyses, and potentially further clinical study, may be required to more fully characterize tanezumab in CLBP patients.”

The new study was published in the journal Pain. Some of its findings had previously been released by Pfizer and Lilly.

FDA Gives Fast Track Designation to New Pain Med

By Pat Anson, Editor

The U.S. Food and Drug Administration has granted “fast track” designation to a new, non-opioid pain medication for patients with osteoarthritis and chronic low back pain -- even though the drug has a history of safety issues.

Tanezumab is an investigational humanized monoclonal antibody that targets nerve growth factor (NGF), a protein that increases in the body as a result of injury, inflammation or chronic pain. Tanezumab binds to NGF and inhibits pain signals from reaching the spinal cord and brain.

Tanezumab is the first NGF inhibitor to receive fast track designation from the FDA, a process that speeds up the development and review of new therapies to treat serious conditions with unmet medical needs.

“If approved, tanezumab would be the first in a new class of non-opioid chronic pain medications,” said Ken Verburg, Chief Development Officer, Neuroscience & Pain, Pfizer Global Product Development. “We believe it would represent an important medical advance in the treatment of debilitating osteoarthritis and chronic low back pain for patients who do not experience adequate pain relief or cannot tolerate currently available pain medications.”

Pfizer is jointly developing tanezumab with Eli Lilly. The two drug makers are currently recruiting patients for Phase 3 studies of tanezumab in 7,000 patients with osteoarthritis, low back pain or cancer pain. Participants will be injected with tanezumab once every eight weeks for treatment periods ranging from 16 to 56 weeks, followed by a 24-week safety follow-up period.  Results from the clinical trials are not expected until next year.

"It is estimated that there are more than 27 million Americans currently living with osteoarthritis and 23 million living with chronic low back pain, many of whom fail to achieve adequate pain relief despite treatment with various types of pain medications,” said Christi Shaw, Senior Vice President and President, Lilly Bio-Medicines.

“We are committed to offering innovative solutions to people suffering from chronic pain conditions, and look forward to working closely with the FDA to facilitate the development of tanezumab.”

Ironically, it was the FDA that slowed the development of NGF inhibitors in 2010 because of safety concerns. The agency ordered a partial halt to clinical studies after Pfizer said a small number of osteoarthritis patients receiving tanezumab experienced worsening of their disease and needed joint replacements. Another safety issue arose in 2012 because the drug caused “adverse changes in the sympathetic nervous system of mature animals.” 

Most clinical studies of tanezumab did not resume until 2015. Pfizer says the current Phase 3 studies include risk mitigation measures for joint safety and sympathetic nervous system safety.

A clinical study of fasinumab, another nerve growth factor drug being developed by Teva and  Regeneron Pharmaceuticals, was stopped by the FDA last year after a patient showed signs of severe joint disease. Regeneron and Teva said they would redesign the study of patients with chronic low back pain to exclude participants with advanced osteoarthritis.