Bupivacaine and liposomal bupivacaine do not produce prolonged perineural anesthesia in a lameness model and are detectable beyond clinical effect in conditioned Thoroughbreds.

The researchers studied the effects and duration of two types of anesthesia, bupivacaine and liposomal bupivacaine, used to treat lameness in horses. They found that liposomal bupivacaine had longer-lasting effects, but neither drug offered prolonged relief from pain and the levels of the drugs in the body were measurable even after their effects had ceased.

Methods

• The study examined 12 conditioned Thoroughbred horses aged between 3 to 10 years, chosen due to their proneness to lameness, a commonly studied clinical condition in horses.
• A reversible lameness model was used to test and compare the effects of bupivacaine hydrochloride (BH) and liposomal bupivacaine (LB).
• The initial phase of the research focused on determining the most effective dose of LB to alleviate grade 2 of 5 lameness, comparing the effects of doses of 25mg BH/nerv, 30mg LB/nerv, 60mg LB/nerv and 133mg LB/nerv.
• Following this, the study pursued a randomized, blind approach to test the pharmacokinetics (how the body metabolizes the drug) and pharmacodynamics (the effects and mechanism of the drug) associated with the chosen optimal doses of LB that eliminated lameness and reduced it for the longest duration.

Results

• The trial revealed that a dose of 133mg/nerve helped eliminate lameness in all the three horses subjected to it.
• The results supported that LB provided analgesia or pain relief for a longer period compared to BH. The return of lameness took longer with LB than it did with BH under both subjective and objective evaluations.
• However, the overall median time until lameness returned was only 12 hours for LB, signifying the therapy’s short-lived effect.
• The terminal half-life (time for half the drug to be eliminated from the body) was similar for both LB and BH, but LB demonstrated an increased area of concentration over time and longer residence time within the body.
• Interestingly, both LB and BH remained detectable in the serum and urine of the horses after the clinical effects had worn off.

Conclusions

• Despite the more prolonged analgesic effect of LB, neither medication provided perineural or nerve-blocking analgesia over long periods.
• While these drugs remain detectable in the body even after their clinical effects cease, high-dose injections of LB are deemed ineffective in providing long-term relief from lameness in horses.