Update on Treatment of Neonatal Septicemia and Failure of Passive Transfer
Sally L, Vivrette, DVM, PhD, DACVIM
North Carolina State University, Raleigh, North Carolina 

Treatment of Neonatal Septicemia

Enrofloxacin

Enrofloxacin, 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.

 A 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 and 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 enrofloxacin was not determined.

Amikacin

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.