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

OBJECTIVE

To measure concentrations of lidocaine serum after application of two 5% patches on horses.

STUDY DESIGN

Prospective experimental trial

ANIMALS

Six client-owned, systemically healthy horses.

METHODS

The hair was clipped on the medial aspect above the carpus of both fore limbs and 2 patches of 5% lidocaine were applied within 30 minutes of jugular catheter placement and the area was then bandaged. Venous blood was drawn from a jugular vein catheter that was inserted using lidocaine as a local block. Samples were drawn immediately before and at 2, 4, 6, 8, and 12 hours after patch application. The presence of lidocaine in serum was determined using an ELISA test.

RESULTS

Lidocaine was detected in the serum of three horses at 0 hours immediately following the local block for catheter placement. Lidocaine was not detected at any other time from 2 to 12 hours. There was mild erythema at the site of patch placement at 12 hours in one horse but this resolved within 1 hour of patch removal. There were no other apparent adverse effects from the patches on any other horse.

CONCLUSION

Five percent lidocaine patches applied proximally to the carpus did not result in detectable systemic concentrations of lidocaine.

CLINICAL RELEVANCE

Any analgesic effects that might be produced by application of 5% lidocaine patches on horses will not be due to systemic absorption of the drug.