Nerve blocks applied to the distal aspect of a limb (distal to the carpus or tarsocrural joint) of horses usually cause desensitization of the area of innervation within 5 minutes. However, it takes at least 20 minutes for nerve blocks that are performed more proximally in a limb to provide desensitization sufficient to cause observable improvement in the gait.2–5 A decrease in the time required to perform some lameness examinations might be achieved by increasing the rapidity of onset of regional nerve blocks.
Chloroprocaine is an ester local anesthetic that is quickly metabolized to para-aminobenzoic acid, which has the potential to cause allergic reactions. For this reason, clinical use of ester local anesthetics has largely been replaced by the use of amide local anesthetics, which have low potential to cause allergic reactions. However, the ester local anesthetics procaine and chloroprocaine are still commonly used in human medicine, primarily for obstetric purposes. Because chloroprocaine has a rapid onset, its use in diagnostic analgesia might be advantageous when performing median or ulnar regional nerve blocks in horses. To our knowledge, no reports exist of the use of chloroprocaine for diagnostic analgesia in horses. The objective of the study reported here was to evaluate onset of analgesia with 3% chloroprocaine hydrochloride and 2% mepivacaine hydrochloride when performing median and ulnar nerve blocks in horses with naturally occurring lameness. We hypothesized that use of 3% chloroprocaine for median and ulnar nerve blocks would result in a more rapid onset but shorter duration of analgesia than when these nerve blocks were performed with 2% mepivacaine.
No third-party funding or support was received in connection with this study or the writing or publication of the manuscript. The authors declare that there were no conflicts of interest.
The authors thank Taylor Gwynn, Cassie Claunch, and Jessica Brown for technical assistance with lameness evaluation of study subjects.
Maximum difference in relative vertical height of the head between right and left halves of the stride
Minimum difference in relative vertical height of the head between right and left halves of the stride
Carbocaine-V, Pfizer Inc, New York, NY.
Nesacaine-MPF, Fresenius Kabi LLC, Lake Zurich, Ill.
The Q, with lameness locator, Equinosis LLC, Columbia, Mo.
PROC MIXED, SAS, version 9.1, SAS Institue Inc, Cary, NC.
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