The stability and microbial contamination of bupivacaine, lidocaine and mepivacaine used for lameness diagnostics in horses.

The study investigates the stability and potential bacterial contamination of local anaesthetics used in equine veterinary practice. A series of tests took place under varied conditions over a period of 16 months which concluded these anaesthetics remain stable and sterile for extended periods under common veterinary field conditions.

Objective of The Study

• The primary aim of this research was to ascertain the physico-chemical stability and bacterial contamination of local anaesthetics, particularly bupivacaine, lidocaine and mepivacaine, which are commonly used for lameness examinations in horses.

Methodology

• The anaesthetics were stored under various conditions that differ in temperature, light intensity and also under common veterinary field conditions.
• The experiment was conducted with 12 different groups for a duration of up to 16 months.
• Parameters like pH, bacterial contamination and concentrations of local anaesthetics and preservatives were recorded serially in both new and repeatedly punctured vials.

Findings of The Study

• According to the study, Mepivacaine remained chemically stable under all tested conditions.
• For Bupivacaine, there were minor changes in concentration – an increase in one group and decrease in other six groups. The factors associated with this change were light and repeated usage of the same vial.
• The concentration of Lidocaine varied depending on the conditions. Exposure to heat and usage of the same vial repeatedly had influence on the degradation of this drug. On the other hand, its storage in practice vehicles led to increase in its concentration.
• Methylparaben, a preservative in Lidocaine, was found to significantly decrease in concentration across seven groups. Risk factors contributing to its degradation were using the same vial many times, exposure to heat and storage in practice vehicles.
• Despite all these changes, none of the tested local anaesthetics showed the presence of bacterial contamination and their pH remained stable all through the examination period.

Conclusion

• The study concludes that the commercially available solutions of the tested local anaesthetics remain extremely stable and sterile under standard veterinary field conditions for extended periods.
• Even though minor changes in concentrations were observed, the researchers believe that these variations are unlikely to affect anaesthetic efficacy during equine lameness examinations.
• The users of these local anaesthetics, especially those containing Methylparaben, should anticipate its degradation over time due to exposure to various conditions like heat and repeated usage of the same vial.