Background/Purpose: Morton’s neuroma (MN) is a painful condition of the third intermetatarsal space caused by distal common digital nerve compression. CNTX-4975 is a highly purified, synthetic, trans-capsaicin that targets the transient receptor potential vanilloid 1, producing analgesia via reversible desensitization of end terminals of primary afferent pain fibers. Prior trial data support the use of injectable CNTX-4975 to treat MN in subjects who fail conservative measures.*

Methods: The primary efficacy endpoint in this phase 2, 12-week randomized, double-blind, placebo-controlled trial was change from baseline to week 4 in the average diary scores for neuroma foot pain with walking using the Numeric Pain Rating Scale. Clinically meaningful pain reduction was defined as ≥30% pain reduction versus baseline. Safety and tolerability assessments included treatment-emergent adverse events (TEAEs) and sensory function examination.

Results: Subjects received a single, ultrasound-guided injection of placebo (n=39), CNTX-4975 200 µg (n=38), or CNTX-4975 600 µg (n=39) following ankle-block anesthesia. Although the primary endpoint did not reach statistical significance, both doses were numerically superior to placebo, with greater clinically meaningful reductions from baseline at weeks 4 and 12. One study site, identified as an outlier site before database lock, had a high placebo rate; in a post-hoc analysis excluding this site, results either achieved (weeks 5 and 12; P<0.05) or neared statistical significance despite a 34% decrease in the number of subjects. The cumulative responder analysis at week 12 showed >90% pain reduction versus baseline for 2% of the placebo group and 40% of the CNTX-4975 200-µg group. In total, 63% of subjects reported ≥1 TEAE (56%, placebo; 74%, CNTX-4975 200 µg; 56%, CNTX-4975 600 µg). No decline was observed in tactile sensibility following injection.

Conclusion: A single injection of CNTX-4975 200 µg or 600 µg for MN provided rapid and prolonged clinically meaningful pain reduction with good tolerability. *Campbell, et al., Pain, 2016.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cntx-4975-trans-capsaicin-injection-provides-clinically-meaningful-pain-reduction-in-subjects-with-painful-intermetatarsal-neuroma-mortons-neuroma-a-randomized-double-blind-placebo-con/