# Acute Dermal Toxicity and Analgesic Effect of a Capsaicinoid Gel Against Formalin-Induced Pain in Wistar Rats

## TL;DR

A capsaicin-based gel was tested in rats for pain relief and safety, showing promising analgesic effects with minimal toxicity.

## Contribution

The study introduces a capsaicinoid gel formulation with demonstrated analgesic efficacy and acute dermal safety in a rodent model.

## Key findings

- The capsaicinoid gel significantly reduced formalin-induced pain in both early and late phases.
- Transient dermal effects occurred at higher doses but resolved without lasting harm.
- Hematological and biochemical changes were mild and within physiological limits.

## Abstract

Background

Pain is a major public health concern, often inadequately managed due to the limitations and side effects of conventional analgesics. Capsicum annuum, widely used in traditional medicine, contains capsaicin, a compound with known analgesic properties. Despite its therapeutic promise, data on the dermal toxicity and efficacy of capsaicin-based topical formulations remain limited.

Objective

The main objective of this study is to evaluate the acute dermal toxicity and analgesic efficacy of a capsaicinoid gel derived from C. annuum in Wistar rats.

Methods

An acute dermal toxicity test was conducted in female Wistar rats using OECD guideline 402. Rats received a single dermal application of 5% capsaicinoid gel at 200, 1000, or 2000 mg/kg and were observed for clinical signs over 14 days. Analgesic activity was evaluated using a formalin-induced paw-licking model. Male rats received topical treatments of capsaicinoid gel (100, 200, or 400 mg/kg) or 1% diclofenac gel (positive control), followed by formalin injection. Pain behavior was scored in early (0-10 minutes) and late (15-60 minutes) phases. Hematological and biochemical parameters were assessed after 21 days.

Results

No mortality was observed. Transient dermal and autonomic effects (e.g., erythema, tremors) were noted at higher doses but resolved spontaneously. The gel significantly reduced formalin-induced pain behaviors in both test phases, particularly at higher doses. Hematological and biochemical parameters showed mild, dose-related changes but remained within physiological ranges.

Conclusion

The 5% capsaicinoid gel exhibited promising analgesic effects and an acceptable safety profile in rats. These findings support its potential as a topical analgesic, warranting further formulation optimization and chronic toxicity evaluation.