Business & Tech

FDA approves Flexion’s osteoarthritis treatment

Hobbled by knee pain?

Federal regulators on Friday approved a new drug for osteoarthritis in the knee that its maker — Burlington-based Flexion Therapeutics Inc. — says provides substantially longer relief than treatments already on the market and could become a blockbuster medicine.

The Food and Drug Administration approved Flexion’s Zilretta, an inflammation-suppressing non-opioid steroid that is delivered through an injection. Although injectables have been marketed for decades, Zilretta uses a novel delivery system. Small particles known as microspheres gradually release the medicine in patients’ joints over an extended period. The company says it provides relief for three months after a single dose, in contrast with other steroid injections that typically relieve pain for only two to four weeks.


“This product has the potential to be transformative,” said Flexion chief executive Michael Clayman, a physician. “We’re thrilled.”

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More than 15 million Americans were diagnosed with osteoarthritis of the knee last year. Over 4 million such patients get conventional steroid injections each year, Clayman said. About half of patients with the painful, progressive condition ultimately seek knee replacements.

Clayman said Flexion will announce a price for the drug within days, but he expects it to be about $500 for each dose. Patients would receive injections in their knees at the office of an orthopedic specialist, a procedure that would take less than a minute.

Industry experts have predicted that the drug could eventually generate $600 million to $1.4 billion annually.

Founded 10 years ago by Clayman and another physician — both veterans of the pharmaceutical giant Eli Lilly and Co. — Flexion has grown to 140 employees and is expected to reach about 270 by the end of the year after adding sales staff.


The FDA granted Zilretta fast-track status in 2015, a designation given to drugs that can offer significant improvement over therapies already on the market.

Knee osteoarthritis has become twice as common since 1950, according to a recent study in the journal Proceedings of the National Academy of Sciences and now affects about one in five American adults 45 or older. The investigators examined knee joints in skeletons dating back thousands of years.

Although some medical specialists have attributed the increase in knee osteoarthritis to the fact that people are living longer and obesity is more common, the study said those factors alone don’t account for the surge.

Among the other potential factors the authors recommended be studied are whether a decline in physical activity over the past 60 years has led to thinner cartilage in joints, whether modern diets rich in refined carbohydrates have worsened chronic mild inflammation, and whether walking on hard pavement exacerbates problems.

Flexion isn’t the only local biotech developing drugs for osteoarthritis in knees.


Centrexion Therapeutics Corp., led by former Pfizer Inc. chief executive Jeffrey B. Kindler, said last December that it was moving from Baltimore to Boston to speed its own pipeline of experimental pain drugs.

Its lead drug candidate is a synthetic form of capsaicin — a medicine derived from the chili plant — that also treats such knee pain, but uses a different approach. It binds to receptors at the end of pain fibers to stop the signal sent to the brain and spinal cord.

Jonathan Saltzman can be reached at