The stability and microbial contamination of bupivacaine, lidocaine and mepivacaine used for lameness diagnostics in horses.
Authors: Adler D M T, Cornett C, Damborg P, Verwilghen D R
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Local Anaesthetic Stability in Field Conditions Diagnostic local anaesthetics are cornerstone tools in equine lameness work, yet little data exists on how storage conditions affect their reliability in practice. Adler and colleagues tested bupivacaine, lidocaine and mepivacaine stability across 12 storage scenarios (ranging from −18 to 70°C, with varying light exposure and field conditions) over 16 months, measuring drug concentration, bacterial growth, pH changes and preservative degradation in both virgin and repeatedly punctured vials. Mepivacaine proved chemically robust with no meaningful changes, whilst bupivacaine and lidocaine showed minor fluctuations (1.9–7.2%) with repeated needle puncture and temperature extremes being the primary destabilising factors; critically, no bacterial contamination developed in any solution and pH remained stable throughout. The findings provide reassurance for field practitioners that commercially available anaesthetic solutions retain clinical efficacy under realistic conditions, though the 8–75% degradation of methylparaben (the preservative in lidocaine formulations) suggests consideration of vial replacement protocols and highlights why mepivacaine's preservative-free stability may offer practical advantages in high-use field settings.
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Practical Takeaways
- •Local anesthetics used for lameness examinations remain safe and effective when stored under typical field conditions for extended periods—you can trust the sterility and efficacy of these products in practice
- •Avoid exposing vials to direct light and excessive heat to minimize concentration changes, and minimize repeated punctures of vials to maintain stability
- •If using lidocaine products, be aware that methylparaben preservative degrades over time (8.3-75% loss), though this does not appear to affect anaesthetic performance during diagnostic procedures
Key Findings
- •Mepivacaine remained chemically stable across all storage conditions tested
- •Bupivacaine showed minor concentration changes (1.9% increase to 3.7% decrease) with light and repeated puncture as risk factors
- •Lidocaine concentration varied 6.3% decrease to 7.2% increase, with heat and repeated puncture vials being risk factors
- •No bacterial contamination was detected in any local anesthetic solution stored under common veterinary field conditions for up to 16 months