Evaluation of the Effect Induced by Repeated Administration of Topical Local Anaesthetic (EMLA) on Itch

Study Overview
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Brief Summary
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In this experiment, the investigators would like to study if the repeated application of local cuaneous anaesthetic EMLA cream will reduce itch induced by small needles from the plant mucuna pruriens (also known as cowhage) and histamine (an itch proving substance formed in the body).

Official Title
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A Mechanistic Evaluation of the Nociceptive Desensitization Induced by Repeated Administration of Topical Local Anaesthetic Mixture of Lidocaine and Prilocaine (EMLA) in a Model of Histaminergic and Non-histaminergic Itch.

Conditions
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Lidocaine, Itch

Intervention / Treatment
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* Drug: EMLA (lidocaine) +Itch (Histamine and cowhage)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Healthy men and women 18-60 years Speak and understand English Exclusion Criteria: Pregnancy or lactation Drug addiction defined as any use of cannabis, opioids or other drugs Previous or current neurologic, musculoskeletal or mental illnesses Lack of ability to cooperate Current use of medications that may affect the trial Skin diseases Consumption of alcohol or painkillers 24 hours before the study days and between these Acute or chronic pain Participation in other trials within 1 week of study entry (4 weeks in the case of pharmaceutical trials) Known history of anaphylactic shock, or local allergy (contact dermatitis) to lidocaine, prilocaine or other local anaesthetics of the amide type.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 60 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
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: EMLA<br> | Drug: EMLA (lidocaine) +Itch (Histamine and cowhage)<br>* Cutaneous anaesthesia: will be topically induced by using EMLA cream 5%, a local anaesthetic cream consisting of equal parts of lidocaine and prilocaine (1g contains 25 mg of lidocaine and 25 mg of prilocaine, AstraZeneca A/S, Albertslund, Denmark). Histamine: To deliver histamine, standard allergy skin prick test (SPT) lancets are applied. Cowhage: Cowhage spicules are 1-2 mm in length and have diameter of 1-3 um at their tip, once inserted into the epidermis, the spicules evoke a moderate sensation of itch and to a lesser extent sensations of burning and stinging pain.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Superficial blood perfusion | is measured by a Speckle contrast imager (FLPI, Moor Instruments, England). | Change from baseline, up to three days after the first session | 
| Warm Detection Thresholds and Heat Pain Thresholds | The tests for thermal sensation will all be performed using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device | Change from baseline, up to three days after the first session | 
| Pain to Supra-threshold Heat Stimuli | The tests for thermal sensation will all be performed using a PATHWAY ATS (Medoc Ltd, Israel) thermal sensory testing device | Change from baseline, up to three days after the first session | 
| Alloknesis | Alloknesis is measured by using mildly pruritic, non-painful von Frey nylon filaments of a predetermined intensity (generally 5-30 miliNewton of force). | Change from baseline, up to three days after the first session | 
| Mechanical Pain Thresholds and Sensitivity | This test is performed using a pin-prick set (Aalborg University, Aalborg). The set consists of 8 needles each having a diameter of 0.6 mm and different force applications: 0.8, 1.6, 3.2, 6.4, 12.8, 25.6, 50.1 and 60.0 g | Change from baseline, up to three days after the first session | 
| Pain rating | The subject will rate the pain for 9 min by using a a visual analog scale (VAS) on a tablet. This scale goes from 0 to 100. 0 indicates 'no pain' and 100 indicates 'worst imaginable pain'. | only on day 3 (third session) | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Itch rating | The subject will rate the itch for 9 min by using a a visual analog scale (VAS) on a tablet. This scale goes from 0 to 100. 0 indicates 'no itch' and 100 indicated 'worst imaginable itch'. | only on day 3 (third session) |