‘Spicy’ Injection Could Take Sting Out of Foot Pain

By Pat Anson, Editor

The U.S. Food and Drug Administration has given "fast track" designation to an injectable pain reliever containing a synthetic form of capsaicin, the active ingredient that makes chili peppers spicy.

The move speeds the development of CNTX-4975 as a treatment for Morton’s neuroma, a painful nerve disorder of the foot. If clinical trials are successful and CNTX-4975 gains full FDA approval, it would be the first use of capsaicin in an injectable analgesic. Capsaicin is already used in skin patches and topical ointments for temporary pain relief.

“We feel the Fast Track designation is recognition that we are pursuing an unmet need for a serious condition with a novel therapy. CNTX-4975 has the potential to help patients avoid surgery, meaning they can avoid the potential complications and recovery associated with surgery, while still achieving the pain relief they are seeking,” said Jim Campbell, MD., founder and President of Centrexion Therapeutics, which is developing the drug.

“We also believe the FDA is trying to encourage development of novel therapies, like CNTX-4975. As a non-opioid, we believe CNTX-4975 could have a major impact in the treatment of chronic pain.”

Centrexion is also studying CNTX-4975 as a possible treatment for osteoarthritis in both humans and dogs.

Morton’s neuroma involves a thickening of the tissue around a nerve leading to the toes, which causes sharp, burning pain in the foot, especially when walking.

The current standard of treatment is steroid injections or surgery to remove the nerve. The surgery often results in permanent numbness in the toes and a potentially long recovery period. 

There are currently no FDA-approved treatments for Morton's neuroma. The agency’s Fast Track process is designed to speed the review of drugs to fill an unmet medical need.


“CNTX-4975 has the potential to provide a high degree and long duration of pain relief without having to undergo surgery. Additionally, CNTX-4975 is highly selective for the capsaicin receptor, which allows it to selectively inactive the local pain fibers while leaving the rest of the nerve fiber functioning, meaning the patient won’t experience numbness in the area of the injection,” said Campbell in an email to PNN.

CNTX-4975 has a short half-life and is cleared from the body within 24 hours, but Campbell says a single injection provides pain relief that lasts for months.

A recent Phase 2b study of CNTX-4975 showed a statistically significant decrease in pain from Morton’s neuroma over a 12-week period. Centrexion plans to begin a Phase 3 trial in 2017.

The company is expecting results later this year on a Phase 2b trial of CNTX-4975 as a treatment for knee osteoarthritis in humans, as well as a study on pet dogs with canine osteoarthritis.

A recent study found that a skin patch containing capsaicin works better than Lyrica (pregabalin) in treating patients with neuropathic pain. Over half the patients using Qutenza had pain relief after about a week, compared to 36 days for those taking pregabalin.