Effects of transdermal lidocaine or lidocaine with prilocaine or tetracaine on mechanical superficial sensation and nociceptive thermal thresholds in horses.

The research article evaluates the effects of lidocaine, and combinations of lidocaine with either prilocaine or tetracaine, when applied transdermally, on superficial sensation and thermal thresholds in horses. The study concluded that these local anesthetic mixtures reduced thermal and mechanical sensation for up to 2 hours.

Research Methodology

• The research was an experimental, randomized study, which involved five healthy adult Warmblood breed horses.
• Selected areas on the horses were clipped at the withers, the cranial saddle area and the caudal saddle area. The animals’ baseline measurements for mechanical superficial sensation and nociceptive thermal thresholds were then noted.
• Next, patches of 5% lidocaine, 2.5% lidocaine/prilocaine cream and 7% lidocaine/tetracaine cream were applied. The lidocaine patch had a 12-hour exposure duration while the other creams had an exposure period of 2 hours.
• In addition to the patches, the researchers performed a micro-perforation on the right side of each application area using a dermaroller with 1200 needles.
• After the respective exposure periods, measurements were undertaken immediately and then hourly for five additional readings at each location. The thermal thresholds were analyzed relative to thermal excursion.
• Statistical analysis was conducted using one- or two-way ANOVA and the Wilcoxon signed-rank test, with significance set at p<0.05.

Research Findings

• The researchers found that micro-perforation prior to the application of the treatments showed no enhancement effect.
• They found that the treatments significantly increased thermal excursion immediately and 1 hour after product removal compared to the baseline thresholds.
• The lidocaine-tetracaine cream decreased superficial mechanical sensation at all measured time points. The lidocaine patch and the lidocaine-prilocaine cream also showed a reduction in superficial mechanical sensation, but not consistently across all the measurements.

Conclusions

• The study concluded that eutectic mixtures of lidocaine with either prilocaine or tetracaine, when applied transdermally, resulted in a reduction of thermal nociception and mechanical sensation for up to 2 hours post-application.
• This has potential implications for pain management in horses, and may lead to improved treatment plans for equine patients requiring local anesthesia.