Pharmacokinetics of intravenous and oral administration of enrofloxacin to the late-term pregnant and non-pregnant mares.
Authors: Ellerbrock R E, Curcio B R, Zhong L, Honoroto J, Wilkins P, Lima F S, Giguere S, Canisso I F
Journal: Equine veterinary journal
Summary
# Enrofloxacin pharmacokinetics in pregnant versus non-pregnant mares Fluoroquinolones offer a valuable therapeutic option for resistant bacterial infections in pregnant mares, yet pregnancy-induced physiological changes could alter drug handling and necessitate dosage modification. Researchers administered single doses of intravenous (5 mg/kg) and oral compounded (7.5 mg/kg) enrofloxacin to six healthy late-gestation mares, then repeated the protocol 45–60 days post-partum following weaning, using LC-MS/MS to quantify drug and metabolite concentrations over 72 hours. Pregnant mares showed significantly higher drug exposure (AUC) following oral administration, with ciprofloxacin (the active metabolite) reaching higher peak concentrations and persisting longer in circulation; intravenous administration revealed similar trends, though differences were less pronounced. Importantly, oral bioavailability remained consistent regardless of pregnancy status, indicating reliable absorption and supporting use of standard dosing protocols for susceptible organisms (MIC <0.25 µg/mL), though pathogens with higher MIC values may require dose escalation or interval adjustment. The modest sample size and assessment only in healthy light-breed mares limit broader application, yet these findings provide reassurance for using enrofloxacin as a treatment option in pregnant mares when bacterial resistance necessitates fluoroquinolone therapy.
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Practical Takeaways
- •Enrofloxacin can be used orally in pregnant mares as an alternative for severe bacterial infections, with well-predictable absorption comparable to non-pregnant horses
- •Current standard dosing intervals appear adequate for susceptible pathogens (MIC <0.25 µg/mL) in both pregnant and non-pregnant mares, though pregnancy does alter drug disposition
- •For resistant bacteria (MIC >0.25 µg/mL), dose adjustments should be considered, particularly in pregnant mares where drug accumulation is more pronounced
Key Findings
- •Enrofloxacin AUC0-∞ was significantly higher in pregnant mares than non-pregnant mares after oral administration and tended to be higher after intravenous administration
- •Ciprofloxacin (enrofloxacin metabolite) showed higher maximum plasma concentration and 24-hour concentration in pregnant mares with longer terminal half-life after oral dosing
- •Oral bioavailability did not differ between pregnant and non-pregnant mares, indicating comparable drug absorption
- •Current recommended dosing is appropriate for bacteria with MIC <0.25 µg/mL; dose adjustment may be needed for MIC >0.25 µg/mL