A trial of 172 patients with knee pain from osteoarthritis, shows that the active component of chili peppers called capsaicin, successfully and significantly reduced pain intensity.
With more than 10% of the population over 60 affected by osteoarthritis knee pain that is incapacitating and not well managed by current therapies, a group of investigators looked to new injectable formulations of capsaicin (already approved for in topical form) for potentially better relief.
The TRIUMPH study1 of an injectable, highly purified synthetic trans-capsaicin (CNTX-4975) formulation reported a significant reduction in pain from osteoarthritis of the knee at 12 weeks. Phase 2b results of the study now available online before publication in Arthritis & Rheumatology found that in dosages of 1.0 mg given as a single intra-articular injection, CNTX-4975 demonstrated a significant and clinically meaningful improvement in moderate to severe osteoarthritis of the knee at 12 weeks that was sustained for up to 24 weeks compared to placebo. A lower dose of 0.5 mg showed a smaller, but still significant reduction in pain at 12 weeks that was not maintained to 24 weeks.
The cohort included 157 patients aged 45-80 with radiographic evidence of chronic osteoarthritis of the knee, enrolled between August 2015 and April 2016 from multiple sites in the US. All had discontinued previous treatments due to inadequate response or had contraindications to standard care.
The initial injection of 1 mg CNTX-4975 was well tolerated and showed a rapid onset of action within 1 week, demonstrated by improvements in walking on a flat surface compared to placebo, and further measured by reduced stiffness, improvement in function according to the patient specific functional scale (PSFS), and patient global assessments of change (PGIC) index.
Long-term safety concerns seemed to be reduced due to a number of factors. The authors noted that “the effects of trans-capsaicin are not dependent on ongoing exposure to the drug; the elimination half-life is less than 4 hours.” Additionally, the single injection and low systemic concentrations of capsaicin in the TRIUMPH trial suggested that no effects beyond the local range of the injection site were expected to occur.
1. Stevens RM, Ervin J, Nezzer J, et al. ized, Double-Blind, Placebo-Controlled Trial of Intra-articular CNTX-4975 (trans-capsaicin) for Pain Associated With Osteoarthritis of the Knee. Arthritis Rheumatol 2019 Mar 19. doi: 10.1002/art.40894.