Pharmacokinetics of amikacin in plasma and selected body fluids of healthy horses after a single intravenous dose.
Authors: Pinto N, Schumacher J, Taintor J, Degraves F, Duran S, Boothe D
Journal: Equine veterinary journal
Summary
# Editorial Summary: Amikacin Pharmacokinetics in Horses Whether a modest single intravenous dose of amikacin achieves adequate therapeutic concentrations across multiple tissue compartments in horses remained unclear until this 2011 investigation. Six mature horses received 10 mg/kg amikacin intravenously, with plasma and body fluid samples (synovial, peritoneal, and interstitial) analysed across time to determine drug distribution and elimination kinetics. Peak plasma concentration reached 144 µg/ml with rapid clearance (half-life 1.34 hours), whilst synovial and peritoneal fluids achieved therapeutic peaks of approximately 20 µg/ml within 1–2 hours; interstitial fluid penetration was more modest at 12.7 µg/ml, though concentrations persisted at 3.31 µg/ml after 24 hours. Against typical Gram-negative pathogens (MIC 4 µg/ml), the plasma concentration-to-MIC ratio of 16.9 substantially exceeded targets for efficacy, though synovial, peritoneal, and particularly interstitial fluid ratios were more marginal at 3–5. For practitioners, these findings support once-daily low-dose amikacin dosing (10 mg/kg) in mature horses for systemic and joint infections caused by susceptible Gram-negative organisms, with the caveat that tissue penetration into interstitial compartments—relevant for soft-tissue and wound infections—is relatively limited, potentially necessitating careful case selection and organism susceptibility confirmation.
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Practical Takeaways
- •Amikacin 10 mg/kg IV once daily is effective for treating Gram-negative bacterial infections in horses based on achieving adequate systemic and tissue concentrations
- •Good penetration into synovial and peritoneal fluids suggests utility for treating joint and abdominal cavity infections, though synovial concentrations are lower than plasma
- •Once-daily dosing is appropriate for mature horses; plasma half-life of ~1.3 hours means drug concentrations decline significantly within 24 hours, reducing nephrotoxicity risk compared to higher-dose regimens
Key Findings
- •A single IV dose of amikacin 10 mg/kg achieved plasma concentration of 144±21.8 µg/ml with elimination half-life of 1.34±0.408 hours in mature horses
- •Amikacin penetrated synovial fluid (Cmax 19.7±7.14 µg/ml at 65±12.2 min) and peritoneal fluid (Cmax 21.4±4.39 µg/ml at 115±12.2 min) with therapeutic potential
- •Mean Cmax:MIC ratio of 16.9±1.80 in plasma exceeded the 4 µg/ml MIC threshold, supporting once-daily dosing efficacy against susceptible Gram-negative bacteria
- •Plasma concentrations fell below detectable levels by 24 hours post-injection, indicating once-daily dosing interval is appropriate