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Background:  Activation by capsaicin of vanilloid receptors (TRPV1) expressed in dermal and epidermal nociceptive sensory nerve fibers results in burning pain sensations followed by functional inactivation of these nociceptors. Low-concentration capsaicin creams are used to treat various neuropathic pain conditions, but are limited by pain and patient non-compliance. In a prior controlled study, a novel high-concentration capsaicin patch resulted in 4 weeks of pain relief after a single 1-hour administration in patients with postherpetic neuralgia, without systemic capsaicin exposure. We report here the results of a pilot study evaluating this investigational treatment in painful HIV-associated distal symmetrical neuropathy.

Methods:  This open-label multi-center study evaluated the tolerability, safety, and efficacy of high-concentration (640 μg/cm²) capsaicin patches in the treatment of HIV-associated distal symmetrical neuropathy. At 3 centers in the United States, 12 patients were treated once and followed for 12 weeks. Treatment consisted of a topical anesthetic application for 1 hour, followed by a 1-hour patch application to the most painful areas of the feet, up to 1000 cm². Patients recorded their pain intensity daily on an 11-point numerical scale. The primary efficacy endpoint was % change from baseline in the “average pain for the past 24 hours” numerical pain score (i.e., average of scores during weeks 2 to 12, compared to baseline).

Results:  Average pain decreased to a mean of 3.2 from a pre-treatment mean of 5.6, corresponding to a decrease of 40% (p = 0.002); 67% of patients experienced a pain decrease of 30% or more, while 33% experienced pain decreases of at least 50%. Pain decrease was noted during the first week after treatment and remained stable throughout the 12-week observation period. Despite expected, self-limited pain increase during and shortly following treatment, overall tolerability was good. Other treatment-related adverse events were usually mild and transient.

Conclusions:  This pilot study demonstrated that the high-concentration capsaicin patch resulted in substantial pain reduction in patients with HIV-associated distal symmetrical neuropathy over 12 weeks after a single 1-hour application. Tolerability was good and no significant safety issues were noted. These promising findings warrant further evaluation in a larger, randomized, controlled study.

Keywords: distal symmetrical polyneuropathy; peripheral neuropathy; capsaicin