Plasma concentration and local anesthetic activity of procaine hydrochloride following subcutaneous administration to horses.
OBJECTIVE
To determine the durations of the local anesthetic effect and plasma procaine concentrations associated with 5- and 10-mg doses of procaine hydrochloride (with or without 100 microg of epinephrine) administered SC over the lateral palmar digital nerves of horses.


METHODS
6 healthy adult horses.


METHODS
The hoof withdrawal reflex latency (HWRL) period was determined by use of a focused heat lamp before and after administration of procaine with and without epinephrine. Blood samples were collected immediately before determination of each HWRL period to assess plasma concentrations of procaine via liquid chromatography-mass spectrometry-mass spectrometry (LC-MS-MS).


RESULTS
10 but not 5 mg of procaine alone and 5 and 10 mg of procaine administered with epinephrine significantly prolonged the HWRL period (mean durations of effect, 5, 120 and 180 minutes, respectively), compared with baseline values. Plasma procaine concentrations did not correlate well with local anesthetic activity; for example, although the HWRL was prolonged to the maximum permitted duration of 20 seconds at 60 to 180 minutes following administration of the 5-mg dose of procaine with epinephrine in certain horses, plasma procaine concentrations were less than the limit of quantitation of the LC-MS-MS assay.


CONCLUSIONS
Small doses of procaine coadministered with epinephrine provided long-lasting local analgesia and resulted in plasma procaine concentrations that were not always detectable via LC-MS-MS. On the basis of these results, the use of regulatory limits or thresholds for procaine concentration in equine plasma samples obtained after racing should be seriously reconsidered.
Kuchembuck
Natasha L
NL
Department of Large Animal Clinical Sciences and Racing Laboratory, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA.
Colahan
Patrick T
PT
Zientek
Keith D
KD
Pirman
David A
DA
Wegner
Kirsten
K
Cole
Cynthia A
CA
D000772:Anesthesia, Local / Q000662:veterinary*; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000097:blood / Q000494:pharmacology*; D000818:Animals; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000097:blood* / Q000502:physiology*; D007279:Injections, Subcutaneous; D008297:Male; D011343:Procaine / Q000008:administration & dosage / Q000097:blood* / Q000494:pharmacology*; D013997:Time Factors
D000779:Anesthetics, Local; D011343:Procaine