EQUINE | Abstracts
Diffusion of enrofloxacin to pregnancy fluids and effects
on fetal cartilage after intravenous administration to late
pregnant mares
R. E. Ellerbrock, I. F. Canisso ,P. J. Roady , L. T. Rothrock, L. Zhong, P. Wilkins, L. Dirikolu, F. S. Lima, J. Honoroto
Background
In selective cases, enrofloxacin may be an alternative
antibacterial agent to treat unresponsive infections
in pregnant mares. Supratherapeutic doses of
enrofloxacin are toxic to adult horses and also to
newborn foals, however, it is unknown if enrofloxacin
crosses the equine placenta or if it is toxic to the fetus.
Objectives
To assess the diffusion of enrofloxacin and its metabolite
to fetal fluids and its effects on fetal cartilage when
administered to pregnant mares.
Study design
In vivo and terminal controlled experiment.
Methods
Healthy mares at 260 days of gestation were allocated
into three groups: untreated (n = 3), therapeutic
treatment (5 mg/kg enrofloxacin, i.v., n = 7) or
supratherapeutic treatment (10 mg/kg, i.v., n = 6)
for 11 days. Fetal fluids were collected on days 1, 5
and 11 of treatment. Premature delivery was induced
on day 11 with oxytocin and fetal fluids and plasma
were collected during delivery. Plasma and fetal
fluid enrofloxacin and ciprofloxacin concentrations
were measured by liquid chromatography–mass
spectrometry. Fetal articular cartilage was examined
macroscopically and histologically for lesions.
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Results
Enrofloxacin and ciprofloxacin reached the minimum
inhibitory concentrations for common pathogens in all
fluids. Ciprofloxacin did not increase with the double
enrofloxacin dose in maternal plasma, but allantoic
fluid showed a 10‐fold increase relative to fetal trough
plasma concentrations. Administration of enrofloxacin
at recommended doses did not result in cartilaginous
lesions in fetuses.
Main limitations
Only one time point in gestation was evaluated and
mares treated in the study were healthy at the time of
treatment. It remains to be determined if enrofloxacin
shows toxicity at other stages of pregnancy, after a
longer duration of treatment, or once the foals are
delivered and articular surfaces are weightbearing.
Conclusions
Short term administration of enrofloxacin to late
gestation mares resulted in detectable enrofloxacin
and ciprofloxacin concentrations in fetal fluids and
did not result in macroscopic or microscopic lesions in
the fetus. While further research is needed to address
long term foal outcomes, enrofloxacin may be useful
for select bacterial infections in pregnant mares.
• Equine Health Update •