Diffusion of fluoroquinolones into equine fetal fluids did not induce fetal lesions after enrofloxacin treatment in early gestation.
Authors: Ellerbrock R E, Canisso I F, Podico G, Roady P J, Uhl E, Lima F S, Li Z
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Enrofloxacin Safety in Early Equine Gestation Fluoroquinolone antibiotics remain underutilised in pregnant mares despite emerging evidence of their safety, largely because practitioners worry about potential chondrotoxic effects during critical periods of fetal skeletal development. Researchers treated six pregnant mares with enrofloxacin (7.5 mg/kg orally for 14 days) between 46 and 60 days gestation—a vulnerable window for cartilage formation—whilst maintaining an untreated control group; four mares were re-bred and crossed over to receive the opposite treatment, serving as their own controls. Both enrofloxacin and its metabolite ciprofloxacin successfully penetrated fetal fluids at measurable concentrations, yet histopathological examination of fetal organs (heart, lungs, spleen, kidney, liver) and limbs revealed no detectable abnormalities in any treated fetuses compared with controls. Whilst this work cannot yet establish long-term safety profiles in born foals, these findings suggest enrofloxacin warrants consideration for select maternal bacterial infections during early pregnancy rather than automatic exclusion, potentially improving treatment options when alternative antibiotics are contraindicated or ineffective. The evidence base remains limited, however, and any fluoroquinolone use in pregnant mares should be reserved for clear clinical indications where benefits demonstrably outweigh theoretical risks.
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Practical Takeaways
- •Enrofloxacin can penetrate fetal tissues during early pregnancy without causing visible skeletal or organ damage over a 2-week treatment period, potentially expanding treatment options for pregnant mares with bacterial infections
- •While this study shows no acute lesions in early gestation, practitioners should note that long-term foal outcomes were not evaluated, warranting continued cautious use with clear clinical justification
- •Consider enrofloxacin as a viable option for select bacterial infections in early pregnant mares rather than automatically withholding fluoroquinolones due to pregnancy status
Key Findings
- •Enrofloxacin and ciprofloxacin diffused into equine fetal fluids during early gestation (46-60 days)
- •No detectable histopathological abnormalities were observed in fetal organs or limbs after 14 days of enrofloxacin treatment (7.5 mg/kg PO)
- •Four mares served as their own controls across two breeding cycles with opposite treatment assignments