on Treatment of Neonatal Septicemia and Failure of Passive Transfer
L, Vivrette, DVM, PhD, DACVIM
Carolina State University, Raleigh, North Carolina
of Neonatal Septicemia
is a broad spectrum gyrase inhibiting antibiotic. There has been
interest concerning the use of enrofloxacin in the treatment of
gram negative sepsis in foals, especially in the presence of an
infectious organism that is resistant to conventional therapy.
However, the pharmacokinetics and safety of this antibiotic has
not been established. At North Carolina State University, we have
performed pharmacokinetic studies in neonatal foals using an intravenous
and oral preparation of enrofloxacin (Baytril). This study, conducted
by Bermingham, et al. (in preparation for publication), included
the administration of a single IV dose of 5 mg/kg when the foals
were 6-7 days of age, followed by a one week washout period before
a single oral dose of 10 mg/kg was administered via a syringe.
In contrast to adult horses, the level of ciprofloxacin detected
in plasma after either dose was negligible. The oral bioavailability
was 43 % and the foals had a longer t ½ elim, larger VDarea
and a lower Cmax. The conclusions of the study suggest that the
oral dose of 10 mg/kg was sufficient to achieve a target AUC/MIC
> 125 for organisms with a MCI >10.5 ug/mL.
chronic oral dose study was also conducted where the gross and
histological changes in articular cartilage of neonatal foals
treated with therapeutic doses of enrofloxacin were investigated.
In this study, 4 foals were administered enrofloxacin orally at
10 mg/kg once daily for 8 doses beginning at 2 weeks of age. Clinically,
3 of the 4 foals became moderately to severely lame with moderate
to severe joint distention (primarily tibio-tarsal joints) beginning
4-6 days after initiation of treatment. On gross examination of
all weight-bearing joints, superficial to full-thickness erosions
cartilage roughening were observed in all foals, most frequently
in the tibial-tarsal joints. Histologically there was cleft and
vesicle formation limited to Zone II of the articular cartilage
with surrounding loss of proteoglycans and mild chondrocyte necrosis.
The results of this study indicate that neonatal foals are similar
to immature animals of other species in their sensitivity to cartilage
damage induced by quinolones, and clinicians should exercise great
caution with their use in young horses. The presence of cartilage
damage in association with the administration of lower doses of
was not determined.
Amikacin pharmacokinetics in sick and healthy neonatal foals have
recently been studied at NCSU by Diane MccFarlane and Rebecca
Tudor at NCSU. The average dose required to achieve therapeutic
concentrations was similar for both healthy and ill neonates:
20-25 mg/kg q24h. Similar findings are reported in healthy foals
by Magdesian et al.. This dosing regimen reduces the risk of nephrotoxicity
and produces more effective, prolonged bacterial killing.