Pharmacokinetics of gentamicin C1, C1a and C2 in horses after single intravenous dose.
Authors: Steinman A, Isoherranen N, Ashoach O, Soback S
Journal: Equine veterinary journal
Summary
# Editorial Summary Gentamicin comprises three active components (C1, C1a, and C2) that exhibit markedly different pharmacokinetic behaviour in horses, yet this distinction had not been characterised until Steinman and colleagues administered a single 6.6 mg/kg intravenous dose to six healthy horses and tracked the clearance patterns of each component individually. The C1a component cleared rapidly from the body—predominantly via glomerular filtration—with a half-life of 2.4 hours and clearance rate of 1.62 ml/min/kg, whilst C1 and C2 components exhibited significantly slower elimination (half-lives of 3.1 and 3.3 hours respectively) and lower clearance rates around 1.05 ml/min/kg. These pharmacokinetic differences have important implications for dosing intervals and the potential for accumulation of certain gentamicin fractions with repeated dosing, as well as variable nephrotoxicity risks depending on which components preferentially accumulate in renal tissue. Practitioners should be aware that gentamicin preparations used in equine practice may behave unpredictably regarding efficacy and safety, since commercial products contain these components in different ratios, and that standard dosing protocols developed in other species may not account for the equine-specific kinetics now documented here.
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Practical Takeaways
- •Different gentamicin components are eliminated at different rates in horses; C1a clears faster suggesting different tissue accumulation profiles that may affect toxicity risk
- •When using gentamicin in horses, the specific component composition of the formulation may influence dosing intervals and duration of therapy needed for efficacy
- •Practitioners should be aware that gentamicin pharmacokinetics differ between components, which could impact nephrotoxicity monitoring and dosing protocols in individual horses
Key Findings
- •Gentamicin C1a clearance (1.62 ml/min·kg) was significantly faster and similar to glomerular filtration rate, compared to C1 (1.03 ml/min·kg) and C2 (1.10 ml/min·kg)
- •Mean residence time and half-life of gentamicin C1a (2.7 h and 2.4 h) were significantly shorter than C1 (3.6 h and 3.1 h) and C2 (3.5 h and 3.3 h)
- •Volume of distribution was similar across all three gentamicin components (0.22-0.26 l/kg), indicating comparable tissue penetration
- •Differential pharmacokinetics between gentamicin components have potential implications for efficacy and toxicity in equine therapy