Pharmacological Modulation of Peripheral Nerve Excitability

Design and method Study design The study is a randomized, double-blinded, placebo-controlled study. To minimize the risk of bias and achieve balance in the allocation of participants and application of creams, block randomization is used. To ensure double blinding, 1-2 colleagues from Center for Neuroplasticity and Pain (CNAP), who is not otherwise involved in the project, will keep the randomization list in a secure room.

Study procedure and experimental test The PTT model will be used to measure the excitability of peripheral sensory afferents. PTT will be measured before and after topical drug application at four distinct areas - two at each side of the volar site of the forearms.

In total four topical creams will be used in the study. One cream containing placebo, one with lidocaine (5%), one with phenytoin (10%) and one with mepyramine (2%).

The study consists of one session lasting 3-4 hrs. The study will include 20 healthy volunteers.

Inclusion criteria

• Men and Women age > 18 years
• Understand and speak Danish
• No medication besides contraceptives

Exclusion criteria

• Pregnancy or lactating women
• Drug addiction (use of cannabis, opioids, or other drugs)
• Use of pain killers, alcohol, or nicotine within the last 24 hours before study start
• Any other medical treatment (e.g., antidepressants, anticonvulsants)
• History of peripheral or chronic pain conditions / neuropathy
• Skin diseases
• Scars and/or tattoos at the volar site of the forearm
• Previous traumatic experience of an electrical accident
• Application of moisturizing lotion of the volar site of the forearms (24 hours before study start)
• Participation in any other research projects/studies 7 days before study start
• Known allergy/intolerance to lidocaine/phenytoin/mepyramine
• Lack of ability to cooperate