Meperidine pharmacokinetics and effects on physiologic parameters and thermal threshold following intravenous administration of three doses to horses.
Authors: Hamamoto-Hardman Briana D, Steffey Eugene P, McKemie Daniel S, Kass Philip H, Knych Heather K
Journal: BMC veterinary research
Summary
# Editorial Summary Meperidine's analgesic potential in horses remains poorly characterised despite clinical use, prompting this investigation into how three escalating intravenous doses (0.25, 0.5, and 1.0 mg/kg) affect pain perception, behaviour and physiology. Eight horses underwent a randomised cross-over trial where researchers measured plasma and urine drug concentrations over 96 hours, monitored heart rate and activity continuously for six hours post-injection, and assessed thermal nociceptive thresholds using a standardised thermal excursion test. The study established the pharmacokinetic profile for each dose whilst documenting effects on vital parameters, gastrointestinal function and pain sensitivity, with thermal threshold changes serving as an objective measure of analgesic efficacy. Understanding meperidine's dose-dependent effects and duration of action in horses helps practitioners make informed choices about dosing regimens for postoperative pain management and acute lameness, whilst the thermal threshold data provides quantifiable evidence of whether higher doses translate to meaningfully improved analgesia. Given the limited literature on systemic meperidine in equines, these findings offer essential pharmacological and clinical data to guide evidence-based analgesic protocols in equine medicine.
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Practical Takeaways
- •Meperidine demonstrates dose-dependent analgesia in horses with improved thermal pain threshold at 0.5–1.0 mg/kg, but clinicians should note the short elimination half-life (~1 hour) may require frequent re-dosing for sustained pain relief
- •This drug produces minimal adverse physiologic effects on heart rate and GI function at tested doses, making it a potentially safer option than some alternative opioids for acute pain management
- •The relatively weak mu-receptor affinity and rapid metabolism suggest meperidine may be most suitable for short-duration analgesic cover rather than prolonged pain management in equine practice
Key Findings
- •Meperidine at 0.25, 0.5, and 1.0 mg/kg IV produced dose-dependent pharmacokinetic profiles with elimination half-lives ranging from 0.8-1.2 hours in horses
- •Higher doses (0.5 and 1.0 mg/kg) significantly increased thermal threshold compared to control, indicating analgesic effects
- •Physiologic parameters including heart rate, gastrointestinal sounds, and packed cell volume showed minimal clinically significant changes across all doses
- •Normeperidine was detectable in plasma and urine, confirming hepatic metabolism of meperidine in horses