title: Antipruritic effect of pretreatment with topical capsaicin 8% on histamine- and cowhage-evoked itch in healthy volunteers: a randomized, vehicle-controlled, proof-of-concept trial.
abstract: BACKGROUND
  Chronic itch is difficult to treat. Low-concentration topical capsaicin (0·006-0·05%) has previously been applied in itch therapy but evidence on its efficacy is contradictory.
  
  
  OBJECTIVE
  This vehicle-controlled, double-blinded study investigated the effect of topical capsaicin 8% after 1- and 24-h application on evoked itch, neurogenic inflammation and itch-associated dysaesthesia.
  
  
  METHODS
  Sixteen healthy volunteers (aged 22 ± 0·5 years, nine female) were treated with capsaicin for 1 h and 24 h, and vehicle for 24 h on each volar forearm. Subsequently, histamine (1%, administered prick test lancets) and cowhage (40-45 spicules) were applied to the pretreated areas. Evoked itch and pain intensities were recorded for 10 min using a visual analogue scale (0-10 cm), while sensitivity to touch-evoked itch was evaluated using von Frey filaments before and after itch provocations. Neurogenic inflammation was assessed using perfusion imaging.
  
  
  RESULTS
  In the vehicle 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 histamine and cowhage after 24-h pretreatment to 1·41 ± 0·58 (P = 0·003) and 0·81 ± 0·18, (P < 0·001), respectively. Capsaicin pretreatment for 1 h reduced only cowhage-induced itch (P = 0·023). Furthermore, 24-h capsaicin pretreatment abolished punctuate hyperknesis and lowered histamine-induced neurogenic inflammation but did not affect weal reactions.
  
  
  CONCLUSIONS
  Topical capsaicin 8% pretreatment for 24 h reduced histaminergic and nonhistaminergic itch by about 75%, while a significant reduction (≈60%) was achieved for only nonhistaminergic itch in a standard 1-h treatment. Further investigations are needed to elucidate the clinical potential of high-concentration capsaicin as an antipruritic.
authors.affiliation: Laboratory for Experimental Cutaneous Pain Research, SMI®, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: H H
authors.initials: HH
authors.lastname: Andersen
authors.affiliation: Laboratory for Experimental Cutaneous Pain Research, SMI®, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: J B
authors.initials: JB
authors.lastname: Marker
authors.affiliation: Laboratory for Experimental Cutaneous Pain Research, SMI®, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: E A
authors.initials: EA
authors.lastname: Hoeck
authors.affiliation: Department of Dermatology and Allergy, Herlev and Gentofte Hospital, Copenhagen University Hospital, Copenhagen, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Elberling
authors.affiliation: Laboratory for Experimental Cutaneous Pain Research, SMI®, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Arendt-Nielsen
mesh_terms: D000279:Administration, Cutaneous; D000982:Antipruritics / Q000008:administration & dosage*; D002211:Capsaicin / Q000008:administration & dosage*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D005542:Forearm; D064368:Healthy Volunteers; D006632:Histamine / Q000009:adverse effects; D006801:Humans; D008297:Male; D031299:Mucuna / Q000009:adverse effects; D011537:Pruritus / Q000517:prevention & control*; D057968:Transdermal Patch; D055815:Young Adult
chemical_list: D000982:Antipruritics; D006632:Histamine; D002211:Capsaicin