Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses.
Authors: Hanafi Amanda L, Reed Rachel A, Trenholme Heather N, Sakai Daniel M, Ryan Clare A, Barletta Michele, Quandt Jane E, Knych Heather K
Journal: Veterinary surgery : VS
Summary
# Editorial Summary: Meperidine Pharmacokinetics in Horses Meperidine has limited clinical utility as an analgesic in equine practice, and this 2021 study sought to clarify whether route of administration might improve its efficacy by comparing intramuscular and subcutaneous dosing at 1 mg/kg in a prospective, randomised, blinded crossover trial involving six horses. Both routes achieved rapid plasma peak concentrations (265.7 ng/mL for IM, 243.1 ng/mL for subcutaneous) within 17–24 minutes, but the drug was eliminated quickly with a terminal half-life of approximately 3 hours, and critically, neither route produced measurable improvements in thermal or mechanical nociceptive thresholds or influenced heart rate, respiratory rate, locomotor activity, or gastrointestinal function over the 24-hour observation period. The absence of detectable antinociceptive effect alongside the short duration of action indicates that meperidine at this dose cannot be relied upon for meaningful pain relief in horses, regardless of whether administered intramuscularly or subcutaneously. Practitioners should consider alternative analgesics—such as alpha-2 agonists, NSAIDs, or opioids with superior pharmacokinetic profiles—when managing equine pain, as meperidine does not meet the threshold for clinical efficacy in this species.
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Practical Takeaways
- •Meperidine at 1 mg/kg is not effective for analgesia in horses via IM or subcutaneous routes and should not be relied upon for pain management in clinical practice
- •The rapid absorption but lack of observable pain relief suggests either insufficient dosing or that meperidine is unsuitable for equine analgesia at this dose
- •Consider alternative analgesic agents with proven efficacy in horses for perioperative or acute pain management
Key Findings
- •Meperidine achieved maximum plasma concentrations rapidly (17±6 minutes IM, 24±13 minutes subcutaneous) with short terminal half-life (~175 minutes) in both routes
- •Neither IM nor subcutaneous meperidine 1 mg/kg produced detectable antinociceptive effects on thermal or mechanical pain thresholds
- •No significant effects observed on heart rate, respiratory rate, locomotor activity, or gastrointestinal function across treatment groups