Continuous monitoring of penicillin G and gentamicin in allantoic fluid of pregnant pony mares by in vivo microdialysis.
Authors: Murchie T A, Macpherson M L, LeBlanc M M, Luznar S, Vickroy T W
Journal: Equine veterinary journal
Summary
# Editorial Summary: Drug Delivery to the Equine Placenta Placentitis in mares has traditionally been managed empirically, with limited evidence guiding antibiotic selection and dosing for intrauterine infections. Researchers used in vivo microdialysis—where ultrasound-guided catheters were placed directly into the allantoic fluid of five healthy pregnant ponies and two with experimentally induced placentitis—to measure how penicillin G, gentamicin, and flunixin meglumine penetrated the placental barrier after intravenous administration. Penicillin G achieved mean peak concentrations of 9.8 µg/ml in uninfected mares and showed markedly prolonged retention in allantoic fluid compared to blood, whilst gentamicin peaked at 8.5 µg/ml with similar kinetics across both compartments; notably, gentamicin concentrations dropped to 3.9 µg/ml in infected mares, suggesting active placental infection may impair drug transfer for this agent. Flunixin meglumine failed to reach detectable levels in allantoic fluid. These findings indicate that penicillin G's extended allantoic persistence potentially justifies extended dosing intervals during placentitis treatment, whereas gentamicin may require higher or more frequent dosing to maintain therapeutic concentrations when placental infection is present—a distinction with significant implications for antibiotic protocols in mares with suspected or confirmed placentitis.
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Practical Takeaways
- •Penicillin G and gentamicin both transfer effectively across the placenta to reach therapeutic concentrations in allantoic fluid, supporting their use in treating equine placentitis
- •Active placental infection may selectively reduce gentamicin transfer, suggesting higher doses or more frequent dosing intervals may be needed in infected mares
- •Penicillin G's prolonged persistence in allantoic fluid compared to blood suggests potential for less frequent dosing intervals in placentitis treatment
Key Findings
- •Penicillin G achieved average peak concentration of 9.8±2.2 µg/ml in allantoic fluid of non-infected mares and persisted much longer in allantoic fluid than blood
- •Gentamicin achieved average peak concentration of 8.5±3.1 µg/ml in non-infected mares but showed reduced concentration (3.9 µg/ml) in mares with experimental placentitis
- •In vivo microdialysis is a useful technique for continuous monitoring of drug concentrations in equine allantoic fluid
- •Flunixin meglumine was not detected in allantoic fluid despite intravenous administration