Ocular penetration of intravenously administered enrofloxacin in the horse.
Authors: Divers T J, Irby N L, Mohammed H O, Schwark W S
Journal: Equine veterinary journal
Summary
# Ocular penetration of intravenously administered enrofloxacin in the horse Leptospira species are commonly identified in equine eyes affected by recurrent uveitis, yet little was known about whether systemically administered antibiotics achieve therapeutic concentrations in the aqueous humour to combat such infections. Divers and colleagues investigated ocular penetration of enrofloxacin by administering 7.5 mg/kg intravenously to six healthy horses and sampling aqueous humour via paracentesis at 1 hour and 23 hours post-injection, with deliberate disruption of the blood-aqueous humour barrier on days 3 and 4 to simulate inflammatory conditions. In undisrupted eyes, mean aqueous humour concentrations reached only 0.32 ± 0.10 mg/l at 1 hour post-administration—below the minimum inhibitory concentration for *Leptospira pomona*—though concentrations increased by day 4 alongside elevated protein levels. Critically, mechanical disruption of the blood-aqueous humour barrier substantially increased enrofloxacin concentrations above the therapeutic threshold, suggesting that intravenous enrofloxacin achieves inadequate ocular penetration in healthy eyes but becomes effective once inflammation compromises the barrier. For practitioners managing horses with leptospiral uveitis, this finding supports enrofloxacin as a systemic adjunct in active inflammatory disease, though the drug's limited penetration in early-stage or non-inflammatory ocular conditions may warrant alternative or additional local therapy.
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Practical Takeaways
- •Enrofloxacin given intravenously at 7.5 mg/kg daily can achieve therapeutic concentrations in the eye for treating Leptospira-associated recurrent uveitis in horses
- •Aqueous humour concentrations increase over time with repeated dosing, suggesting accumulation or improved penetration by Day 4 of therapy
- •In horses with inflammatory uveitis where the blood-ocular barrier is already compromised, enrofloxacin penetration to the eye is enhanced, supporting its use in active ocular infections
Key Findings
- •Intravenous enrofloxacin at 7.5 mg/kg every 24 hours achieves aqueous humour concentrations exceeding the MIC for Leptospira pomona
- •Mean aqueous humour enrofloxacin concentration 1 hour post-administration on Day 3 was 0.32 ± 0.10 mg/L (range 0.18–0.47 mg/L)
- •Aqueous humour concentrations and aqueous humour:plasma ratios were significantly higher on Day 4 compared to Day 3
- •Mechanical disruption of the blood-aqueous humour barrier via paracentesis increases both enrofloxacin and protein concentrations in aqueous humour, achieving concentrations above the Leptospira pomona MIC