Intraosseous gentamicin perfusion of the distal metacarpus in standing horses

Objective-To report tissue gentamicin concentrations after intraosseous (IO) perfusion in standing horses. Study Design-In vivo study. Animals or Sample Population-Twelve horses. Methods-Sedated horses had a cannulated cortical bone screw inserted into the dorsolateral aspect of the treated metacarpus and a tourniquet applied proximally. Gentamicin (2.2 mg/kg) diluted in sterile saline solution (0.1 mL/kg) was infused through the screw. Two horses were euthanatized at each time interval: 0, 2, 6, 12, 24, and 36 hours. Synovial fluid and bone samples were collected distal to the screw from both forelimbs. Gentamicin concentrations were measured using fluorescence polarization immunoassay. Results-The highest synovial fluid gentamicin concentrations were 385 +/- 273 mug/mL (mean +/- SD) in the metacarpophalangeal joint, 225 +/- 205 mug/mL in the proximal interphalangeal joint, 215 +/- 205 mug/mL in the distal interphalangeal joint, 382 +/- 195 mug/mL in the digital flexor tendon sheath, and 206 +/- 161 mug/mL in the navicular bursa. The highest bone concentrations of gentamicin were 55 +/- 30 mug/g in the distal metacarpus, 34 +/- 27 mug/g in the proximal, 16 +/- 15 mug/g in the middle, and 16 +/- 2.2 mug/g in the distal phalanges, and 27 +/- 17 mug/g in the proximal and 24 +/- 11 mug/g in the distal sesamoid bones. Conclusion-Standing 10 perfusion of gentamicin resulted in local antibiotic concentrations in the synovial structures and bones of the distal aspect of the limb that exceed the reported minimum inhibitory concentration of pathogens commonly implicated in equine orthopedic infections. Clinical Relevance-Standing IO perfusion of gentamicin in the distal aspect of the limb should be considered for treatment of orthopedic infections of this region in horses. (C) Copyright 2004 by The American College of Veterinary Surgeons.