A Human Experimental Model for Neuropathic Pain Using Combined Application of Capsaicin and Local Anesthetics

Study Overview
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Brief Summary
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Main of the present study was to develop a model of concomitant C-fibre block and sensitization eliciting spontaneous pain as well applying topical capsaicin and local anesthetics (LA) to examine the sensory alterations after combined C-fiber block and sensitization in both different application orders (sensitization of blocked C-fibers and block of sensitized C-fibers), compared to each of both mechanisms alone. Thereby, we expect stronger sensory changes during the combined substance application than during the monoapplication. We expect also contralateral sensory alterations mirroring the changes on the intervention site after the combined capsaicin and LA application, being stronger than after sensitization alone absent after C-fiber block alone.

Conditions
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Ipsi- and Contralateral Hypoesthesia

Intervention / Treatment
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* Procedure: Application of capsaicin 0.6%
* Procedure: Application of local anesthetics (EMLA plaster)
* Procedure: Application of 1 capsaicin 0.6% and 2. EMLA
* Procedure: Application of 1. EMLA and 2. capsaicin 0.6%


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: healthy subject, older than 18 years, provided written informed consent Exclusion Criteria: insufficient comprehension of the German language, history of severe internal, neurological or dermatological diseases, substance abuse, manifest psychiatric diseases, chronic and acute pain, any medication intake (except contraceptives in females) regularly or on demand during the last 14 days before study inclusion and during the study period, hypersensitivity to lidocaine or other amide-type anesthetics, hereditary or acquired methemoglobinemia, pregnancy, nursing, abnormal sensory profile in the quantitative sensory testing (QST) with side-to-side differences beyond the normal range at baseline and participation in clinical trials during the last month.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 90 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Capsaicin application<br>application of 0.6% | Procedure: Application of capsaicin 0.6%<br>* topical application of 0.6% capsaicin on the volar forearm<br>|
| Experimental: Local anesthetics application<br>application of EMLA | Procedure: Application of local anesthetics (EMLA plaster)<br>* topical application of EMLA on the volar forearm<br>|
| Experimental: Combined application of 1. capsaicin 2. local anesthetics<br>application of 1. capsaicin 0.6% and 2. EMLA | Procedure: Application of 1 capsaicin 0.6% and 2. EMLA<br>* topical application of 1. 0.6% capsaicin and 2. EMLA on the volar forearm<br>|
| Experimental: Combined application of 1. local anesthetics and 2. capsaicin<br>application of 1. EMLA and 2. capsaicin 0.6% | Procedure: Application of 1. EMLA and 2. capsaicin 0.6%<br>* topical application of 1. EMLA and 2. 0.6% capsaicin on the volar forearm<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| grade of the ipsi- and contralateral hypoesthesia |  | 6 months | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| area of the ipsi- and contralateral hypoesthesia |  | 6 months |