Effect of Meperidine on Equine Blood Histamine, Tryptase, and Immunoglobulin-E Concentrations.
Authors: Trenholme H Nicole, Sakai Daniel M, Berghaus Londa J, Hanafi Amanda L, Knych Heather K, Ryan Clare A, McHale Brittany, Banovic Frane, Quandt Jane E, Barletta Michele, Reed Rachel A
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Meperidine and Equine Immune Response Meperidine is a commonly used opioid analgesic in equine practice, yet concerns have been raised about its potential to trigger mast cell degranulation and hypersensitivity reactions; this study investigated whether subcutaneous or intramuscular administration provokes measurable immunological changes by quantifying plasma histamine, tryptase, and serum IgE across six horses in a randomised crossover design with saline controls. Blood sampling at multiple time intervals (histamine at 5–60 minutes, tryptase to 240 minutes) combined with enzyme-linked immunosorbent assay and liquid chromatography-mass spectrometry analysis revealed no statistically significant elevations in any of the three immunological markers regardless of route or dose, with no differences observed between meperidine and saline treatments. Notably, whilst systemic immune activation did not occur, two horses receiving subcutaneous meperidine developed localised vasculitis, thrombosis, regional oedema, and haemorrhage at the injection site—findings supported by tissue biopsy. For equine practitioners, these results provide reassurance that meperidine at 1 mg/kg does not provoke anaphylactoid reactions or systemic mast cell degranulation via either route; however, the local tissue damage associated with subcutaneous injection suggests intramuscular administration may be preferable to minimise injection-site complications, particularly given the lack of pharmacological advantage to subcutaneous dosing.
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Practical Takeaways
- •Meperidine does not trigger systemic anaphylactoid or anaphylactic reactions in horses, making it safe from an immunological standpoint
- •SC meperidine causes localized tissue damage (vasculitis, thrombosis) even without systemic immune activation—prefer IM administration to avoid injection site complications
- •Horses with prior meperidine exposure do not develop elevated baseline IgE, suggesting no allergic sensitization occurs with repeated use
Key Findings
- •No statistically significant elevations in plasma histamine, tryptase, or IgE following IM or SC meperidine administration (p > 0.05 for all parameters)
- •Subcutaneous meperidine caused localized vasculitis, thrombosis, regional edema and hemorrhage in injection sites despite absence of systemic anaphylactoid response
- •No differences in immunological parameters between IM and SC routes of meperidine administration