Effects of high-dose gentamicin sulfate on neuromuscular blockade in halothane-anesthetized horses.

OBJECTIVE To evaluate effects of a single high dose of gentamicin on neuromuscular function in horses anesthetized with halothane. ANIMALS 6 healthy adult horses. PROCEDURE Halothane-anesthetized horses were positioned in left lateral recumbency, and the right hind limb was immobilized in a reusable fiberglass cast fixed to a steel frame. The hoof was attached to a force transducer, and resting tension of 0.93 +/- 0.16 kg was maintained. A supramaximal train-of-four stimulus of 2 Hz for a duration of 0.25 millisecond was applied to the superficial peroneal nerve every 20 seconds by a square-wave stimulator. The force of the evoked digital extensor tension was recorded to determine first muscle twitch tension, compared with the baseline value (T1%) and the ratio of the force of the fourth twitch to the first twitch (T4/T1). Data were recorded at 5, 10, 15, 30, and 60 minutes after i.v. administration of vehicle or gentamicin (6 mg/kg of body weight). RESULTS There was a significant (P = 0.04) treatment-time interaction for the effect of gentamicin on T1%; T1% associated with vehicle decreased from 100% to 92% during the 60- minute study period, but no decrease was associated with gentamicin. For T4/T1, there was no significant effect of treatment or time or treatment-time interaction between gentamicin and vehicle. CONCLUSIONS Gentamicin did not cause a decrease in initial muscular strength, nor did it impair the muscles' ability to sustain strength. CLINICAL RELEVANCE A single high dose of gentamicin does not cause significant neuromuscular blockade when administered alone to healthy horses anesthetized with halothane.