Lack of systemic absorption of lidocaine from 5% patches placed on horses.

This research study evaluated the absorption levels of lidocaine in horses when applied via a 5% lidocaine patch and found no systemic absorption of the drug, suggesting that any pain-relief effects are not due to the drug entering the bloodstream.

Study Overview

The study aimed to investigate whether or not a 5% lidocaine patch applied to horses results in the medication being absorbed into the bloodstream of the horse. The researchers used a sample of six healthy horses for the experimental trial.

Methods

• The team initiated the experiment by grooming the horses, clipping the hair on a specific part of their forelimbs, and applying two patches of 5% lidocaine. The patches were applied within 30 minutes of establishing a jugular catheter.
• Blood samples were collected from a catheter inserted into a jugular vein. The area for catheter insertion was temporarily numbed with lidocaine to reduce any discomfort.
• Blood samples were collected immediately before patch application and then at regular intervals for up to 12 hours afterwards – at 2, 4, 6, 8, and 12 hours post-applications.
• The collected blood samples underwent an ELISA test to detect the presence of lidocaine in the bloodstream.

Results

• The results showed that traces of lidocaine were found in the bloodstream of three horses immediately after the local numbing for catheter placement, as expected.
• However, no traces of lidocaine were detected in any of the horses’ bloodstream at all subsequent sampling times up to 12 hours after patch application.
• Only minor side effects were observed, with one instance of mild skin redness at the patch site that resolved within an hour of patch removal.

Conclusions

• The researchers concluded that the administration of a 5% lidocaine patch on horses does not seem to result in the absorption of the drug into the systemic circulation.
• This information implies that any potential pain-relieving effects from the application of lidocaine patches are not due to the systemic absorption of the drug into the horse’s body but likely due to localized numbing where the patch was applied.