Antipruritic effect of pretreatment with 8% topical capsaicin on histamine- and cowhage-evoked itch in healthy volunteers – a randomized placebo-blinded proof-of-concept trial

Abstract

Background

Chronic itch is difficult to treat and associated with significantly decreased life quality. Topical low-concentration capsaicin (0.006-0.05%) has previously been investigated and applied in therapy of itch but contradictory evidence exits regarding its efficacy.

Objectives

This placebo-controlled, double-blinded study investigated the effect of 8% topical capsaicin applied for 1 and 24 hours on evoked itch, neurogenic inflammation and itch-associated dysesthesia.

Methods

Sixteen healthy volunteers (22±0.5 years, 9F) were treated with capsaicin for 1h and 24hrs, and vehicle for 24hrs on each volar forearm. After capsaicin/vehicle application, histamine (1%, administered prick test lancets) and cowhage (40-45 spicules) were applied in pretreated areas. Evoked itch and pain intensities were recorded for 10 minutes using a visual analog scale (0-10 cm), while Sensitivity To Touch-evoked Itch (STTI) was evaluated using von Frey filaments before/after itch provocations (as a measure of punctuate hyperknesis). Neurogenic inflammation was assessed using perfusion-imaging.

Results

In the vehicle-pretreated areas peak itch responses to histamine and cowhage were 4.67±0.58 and 5.15±0.71, respectively. Capsaicin-pretreatment reduced peak itch responses to both histamine and cowhage, after 24-hour pretreatment to 1.41±0.58 (p=0.003) and 0.81±0.18, (p<0.001), respectively. 1-hour capsaicin-pretreatment only reduced cowhage-induced itch (p=0.023). Furthermore, 24-hours capsaicin-pretreatment abolished punctuate hyperknesis and lowered histamine-induced neurogenic inflammation but did not affect wheal reactions.

Conclusions

Twenty-four hours of topical 8% capsaicin-pretreatment reduced histaminergic and non-histaminergic itch by ≈75%, while only significant reduction was achieved for non-histaminergic itch in a standard 1-hour treatment. Further investigations are needed to elucidate the clinical potential of high-concentration capsaicin as an antipruritic.

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