The concentration of lidocaine and mepivacaine measured in synovial fluid of different joints of horses after single intra-articular injection.

The research focuses on the study of the concentrations of anesthetics, lidocaine and mepivacaine, found in the synovial fluid of horses’ joints after being injected with regulated clinical dosages. It aims to juxtapose the respective concentration levels with the ones proven to exhibit cytotoxicity and antimicrobial activity.

Study Design and Procedure

• The research was set into two parts wherein four distinctive joints of a horse were considered – Distal interphalangeal (DIP), Metacarpophalangeal (MCP), Middle carpal (MC), and tarsocrural (TC). The plan was to inject the said anesthetics into these joints and then examine the synovial fluid for traces of these.
• In the first part of the experiment, 20 joints of five horses, under general anesthesia, were injected with clinically approved quantities of 2% Lidocaine, while 19 similar joints received 2% Mepivacaine. The synovial fluid samples were collected roughly 7 minutes after the injection.
• The second part mirrored the first with only a difference in time, as the samples were collected approximately 23 minutes post-injection.
• The detection of Mepivacaine and Lidocaine residue traces in the synovial fluid samples was done using a High-Performance-Liquid-Chromatography with Mass Spectrometry detection (HPLC MS).

Observations and Results

• The concentrations of both the anesthetics were found and recorded. For instance, in the first experiment’s synovial fluid, Lidocaine concentrations ranged between 6.46 to 19.62 mg/mL (mean=11.96 ± SD 3.89 mg/mL), while Mepivacaine’s concentrations fell between 5.01 to 13.38 mg/mL (mean=8.18 ± SD 1.76 mg/mL).
• Similarly, in the second experiment, the concentrations for Lidocaine were found to be 2.94-10.40 mg/mL (mean=6.31± SD 2.23 mg/mL) and for Mepivacaine, they were 2.10-8.70 mg/mL (mean=4.97 ± SD 1.77 mg/mL).
• The researchers observed that the concentrations of both anesthetics reduced considerably in the second experiment, with the quantities being 33-60% lower than in the first experiment.

Conclusions

• From the research, it was conclusively found that Intra-articular injections in horses result in synovial fluid concentrations higher than those known to be associated with cytotoxic effects.
• Interestingly, these also exceeded levels associated with beneficial antimicrobial activities.