title: Intradermal capsaicin causes dose-dependent pain, allodynia, and hyperalgesia in humans.
abstract: BACKGROUND
  Intradermal capsaicin is a human pain model that produces reliable pain and sensitization. This model facilitates controlled testing of analgesic efficacy via a crossover design while minimizing confounding variables in clinical pain states and retaining sufficient power with small samples.
  
  
  METHODS
  To determine the lowest dose of capsaicin that produces consistent neurosensory measures, we administered 0.1, 1, 10, or 100 microg to healthy volunteers in a blinded manner (N = 19). Pain scores were recorded at 0, 5, 10, 15, and 60 minutes on a visual analog scale from 0 to 100. Areas and intensities of mechanical allodynia (foam brush stimulus) and pinprick hyperalgesia (von Frey test) were quantified at 15 and 60 minutes, as were flare areas.
  
  
  RESULTS
  Capsaicin produced dose-dependent increases in spontaneous pain (p = .013), the area and intensity of mechanical allodynia (p = .006 and p < .001, respectively), the area and intensity of pinprick hyperalgesia (p = .010 and p = .014, respectively), and the flare area (p = .010). The 10 microg dose produced greater spontaneous pain than the 1 microg dose (p = .017). The 100 microg dose produced greater spontaneous pain than the 10 microg, but the difference was not statistically significant.
  
  
  CONCLUSIONS
  The 10 and 100 microg capsaicin doses produced robust pain measures across a range of modalities, and lower doses produced minimal effects. Whereas most studies use 100 microg, using a lower dose is reasonable and may facilitate detection of subtle analgesic effects--particularly with nonopioid analgesics--and drugs can be tested in lower doses, minimizing adverse side effects.
authors.affiliation: Department of Anesthesiology and the Center for Pain and Palliative Medicine, University of California, San Diego School of Medicine, La Jolla, CA 92093-0924, USA.
authors.forename: Graham C
authors.initials: GC
authors.lastname: Scanlon
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wallace
authors.forename: J Sorin
authors.initials: JS
authors.lastname: Ispirescu
authors.forename: Gery
authors.initials: G
authors.lastname: Schulteis
mesh_terms: D000328:Adult; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced*; D007271:Injections, Intradermal; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000139:chemically induced*
chemical_list: D002211:Capsaicin