Pharmacokinetics of amikacin after intravenous, intra-articular, and combined intravenous and intra-articular administration in healthy neonatal foals.
Authors: Paegelow Jillian L, Schoonover Mike J, Young Jenna M, Maxwell Lara K, Taylor Jared D, Gilliam Lyndi L, Holbrook Todd C
Journal: Journal of veterinary internal medicine
Summary
# Amikacin Dosing in Neonatal Foals: Navigating Combined IV and Intra-articular Routes Aminoglycoside therapy is common in neonatal foal medicine, yet the plasma pharmacokinetics of amikacin when administered jointly via intravenous and intra-articular routes—a strategy increasingly used to manage septic arthritis whilst maintaining systemic coverage—remain poorly characterised. Researchers administered three treatment protocols to eight healthy neonatal foals across three age windows (7–9, 14–16, and 21–23 days old): IV-only dosing (25 mg/kg every 24 hours), concurrent IV and IA dosing split between routes (16.7 mg/kg IV and 8.3 mg/kg intra-articularly to the tarsocrural joint), and IA-only dosing. Peak plasma concentrations at 30 minutes proved significantly age-dependent, with the IV-only protocol consistently achieving therapeutic levels (≥53 μg/mL) across all age groups, whilst the combined protocol fell short in the youngest foals (46.5 μg/mL in 7–9-day-olds) but met targets from 14 days onward. Clinically, this means practitioners using combined IV and IA amikacin for suspected septic arthritis in foals under two weeks old risk subtherapeutic systemic exposure, particularly against organisms with intermediate susceptibility, suggesting either dose escalation of the IV component or careful monitoring in this critical age group. For foals aged 14 days and beyond, the combined approach appears efficacious, offering joint penetration without sacrificing adequate systemic concentrations.
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Practical Takeaways
- •If using combined IV and IA amikacin dosing in neonatal foals under 2 weeks old, monitor plasma concentrations closely or consider full IV dosing, as combined protocols may not achieve therapeutic levels against intermediate-susceptibility organisms
- •Age-dependent pharmacokinetics mean dosing protocols should account for foal maturity; younger foals require higher mg/kg doses or different regimens to achieve equivalent plasma concentrations
- •Standard IV-only amikacin dosing (25 mg/kg q24h) reliably achieves therapeutic concentrations across the neonatal period and may be safer than split IV/IA protocols for systemic infections in very young foals
Key Findings
- •IV-only amikacin (25 mg/kg q24h) achieved therapeutic plasma concentrations (≥53 µg/mL at 30 min) across all age groups tested (7-23 days old)
- •Combined IV and IA administration (16.7 mg/kg IV + 8.3 mg/kg IA q24h) failed to reach therapeutic concentrations in 7-9 day old foals (46.5 µg/mL) but succeeded in older foals (14-23 days old, 62.6-62.9 µg/mL)
- •Foal age significantly influenced amikacin pharmacokinetics, with older foals (21-23 days) showing higher 30-minute plasma concentrations than younger foals across protocols
- •IA-only administration route was tested but plasma contribution data suggests minimal systemic absorption from intra-articular injection alone in neonatal foals