Topical Acetaminophen for Itch Relief: a Proof of Concept Study in Healthy Subjects

Topical Acetaminophen for Itch Relief: a Proof of Concept Study in Healthy Subjects

Currently, topical antihistamines and corticosteroids are mainly used for itching relief. However, the over the counter antihistamines are not effective on all itch conditions. Acetaminophen is a popular and widely used OTC drug for pain relief. Although its mode of action is still unknown, recent studies have shown that acetaminophen indirectly activates cannabinoid CB1 receptors. Recent studies have shown that topical cannabinoid agonists are effective for itch relief, the efficacy of topical acetaminophen will be tested for non-histaminergic itch relief.

This will be a single-blinded, vehicle-controlled randomized study in healthy controls to test the efficacy of the topical gel formulation with three differing concentrations of acetaminophen (APAP) for itch relief. To detect medium effects of the treatments with a given α of 0.5 and an error probability of 0.05, with a power of 0.95, the number of participants needed is 36 (10 within post hoc pairwise comparisons).

Inclusion Criteria:

1. Healthy subjects must be between 18 and 50 years of age.
2. Must be in general good health with no disease or physical conditions that would impair evaluation of itch and pain perception.
3. No history of chronic itch or pain.
4. Must abstain from the use of any systemic or topical anti-histamine, steroid, or pain relief medications from the week prior to the study till the completion of the study.
5. Must abstain from the use of moisturizers on the arms 24 hours before study visits.

Exclusion Criteria:

1. Individuals under 18 or over 50 years of age.
2. Inability to complete the required measures.
3. The presence of an itchy skin disease.
4. Diagnosis of diseased that would affect itch or pain perception (e.g. neuropathies).
5. Currently enrolled in any investigational study in which the subject is receiving any type of drug, biological, or non-drug therapy.
6. Use of oral, topical analgesics, or other medications known to interfere with itch or pain perception in the week prior to the study and throughout the study (e.g. antihistamines, anesthetics, opioids, neuroleptics, etc.).
7. Use of emollients on the arms a week prior to the study and throughout the study.
8. Known allergies to acetaminophen and cowhage.
9. Pregnant women. (Women of child bearing potential will undergo an hCG pregnancy test).
10. Currently incarcerated.