Morphine plasmatic concentration in a pregnant mare and its foal after long term epidural administration.
Authors: Mirra Alessandro, Birras Jasmin, Diez Bernal Sabina, Spadavecchia Claudia
Journal: BMC veterinary research
Summary
# Editorial Summary Epidural morphine offers valuable analgesia in equine practice, yet current dosing protocols rely on clinical experience rather than robust pharmacokinetic data, creating particular uncertainty in physiologically altered states such as pregnancy. This case report tracked plasma morphine concentrations and metabolite levels in a gravid mare receiving prolonged epidural administration and subsequently in her foal, providing rare species-specific insight into drug distribution during gestation and early neonatal exposure. The findings demonstrate altered morphine kinetics in the pregnant mare compared to published non-pregnant data, with measurable transfer to the foal via placental circulation, highlighting the unpredictability of empirical dosing schemes in this population. Understanding these concentration profiles is essential for equine practitioners managing pregnant mares requiring analgesia, as underdosing risks inadequate pain relief whilst overdosing increases the likelihood of side effects in both dam and offspring. Future evidence-based dosing recommendations for epidural morphine in pregnant horses should incorporate these pharmacokinetic parameters to optimise analgesia whilst minimising neonatal exposure and maternal complications.
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Practical Takeaways
- •Morphine and active metabolites cross the placenta during pregnancy—use epidural morphine in pregnant mares only when benefits clearly outweigh potential fetal exposure risks
- •Current dosing recommendations for epidural morphine lack robust pharmacokinetic data in horses; clinical judgment and careful monitoring are essential, particularly in pregnant or physiologically compromised animals
- •Consider alternative analgesic strategies or lower epidural morphine doses in pregnant mares; foals born to treated dams should be monitored for signs of opioid effects
Key Findings
- •Morphine and its metabolites (M3G and M6G) were detectable in both pregnant mare and foal plasma following prolonged epidural morphine administration
- •Epidural morphine administration during pregnancy resulted in transplacental transfer of morphine to the fetus
- •Foal plasma morphine concentrations were measurable postnatally, indicating significant fetal exposure during gestation
- •Species-specific pharmacokinetic data for equine epidural morphine remains limited and empirical dosing may be unpredictable in physiologically altered states such as pregnancy