Topical Tripelennamine 1% Cream Versus Diphenhydramine 1% Cream for the Relief of Histamine-Induced Itching: A Proof Concept Study in Healthy Adults.

The goal of this clinical trial is to determine whether tripelennamine 1% topical cream is effective in relieving histamine-induced itching and skin reactions and whether it is more effective than diphenhydramine 1% topical cream in healthy adult volunteers aged 18 to 50 years with no history of chronic itch or conditions affecting itch perception. The study was conducted because there are limited over-the-counter topical medications that directly relieve acute itch, creating a need for more effective topical antipruritic treatments.

The main questions it aims to answer are:

• Does tripelennamine 1% cream reduce the intensity of histamine-induced itch, as measured by a visual analog scale (VAS), including overall itch intensity (area under the itch-time curve), peak itch severity, and duration of itching?
• Does tripelennamine 1% cream reduce histamine-induced skin reactions, specifically the magnitude and duration of flare and wheal responses, compared with diphenhydramine 1% cream and vehicle control? Researchers will compare tripelennamine 1% topical cream, diphenhydramine 1% topical cream, and a vehicle control cream base to determine whether tripelennamine provides superior relief of histamine-induced itch and associated skin reactions. The investigators hypothesized that participants treated with tripelennamine would experience significantly less itching and reduced flare and wheal responses following a histamine challenge than those treated with diphenhydramine or vehicle control.

Participants will:

• Provide informed consent and undergo screening to confirm eligibility.
• Have four 4 cm × 4 cm test areas marked on the inner surfaces of both forearms.
• Receive randomized, double-blinded applications of:
• Tripelennamine 1% topical cream,
• Diphenhydramine 1% topical cream, and
• Vehicle control cream base.
• Have approximately 0.2 g of each study cream applied to designated skin sites and left in place for 15 minutes.
• Undergo a histamine challenge at each treatment site using iontophoresis, a procedure that delivers histamine 1% gel through the skin using a low electrical current to induce itching and the characteristic histamine wheal-and-flare response.
• Rate the intensity of itching every minute using a 0 to 10 visual analog scale, where 0 represents "no itch" and 10 represents the "worst itch imaginable," until the sensation completely resolves.
• Have the duration and peak severity of itching recorded for each treatment condition.
• Have skin flare and wheal reactions assessed and scored every 5 minutes for up to 20 minutes after the histamine challenge.
• Have photographs and videos taken of the treatment sites to document flare and wheal responses over time.
• Be monitored for adverse events during the study and report any adverse effects for up to one week after study completion.

This was a single-center, randomized, double-blind, vehicle-controlled clinical trial conducted at Palm Beach Atlantic University. Thirty-seven healthy adults were enrolled and thirty-six participants completed all efficacy assessments included in the final analysis.

Inclusion criteria

• Must be in general good health with no disease or physical conditions that would impair evaluation of itch and pain perception.
• No history of chronic itch or pain.
• Must abstain from the use of any systemic or topical antihistamine, steroid, or pain relief medications from the week prior to the study till the completion of the study.
• Must abstain from the use of moisturizers on the arms 24 hours before study visit.

Exclusion criteria

• Inability to complete the required measures.
• The presence of an itchy skin disease.
• Diagnosis of disease that would affect itch or pain perception (e.g. neuropathies).
• Currently enrolled in any investigational study in which the subject is receiving any type of drug, biological, or non-drug therapy.
• 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.).
• Use of emollients on the arms a week prior to the study and throughout the study.
• Known allergies to tripelennamine and/or diphenhydramine.
• Pregnant women. (Women of childbearing potential will undergo an hCG pregnancy test).