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

The research experimented on healthy adult horses to assess the impact of a high dose of the drug gentamicin on neuromuscular function during anesthesia with halothane. Surprisingly, it was found that a single high dose of gentamicin does not cause notable neuromuscular blockade, meaning it did not decrease initial muscular strength or impair muscle strength sustainability.

Methodology

• Six healthy adult horses were anesthetized with halothane and positioned in left lateral recumbency. This method could mimic the conditions where a horse would need to undergo a surgical procedure requiring anesthesia and immobilization.
• The right hind limb of each horse was immobilized using a reusable fiberglass cast attached to a steel frame and the hoof was linked to a force transducer. This was done to measure the muscle tension generated by the horse as a response to electric stimulations.
• A tension of 0.93 +/- 0.16 kg was maintained at rest and 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 using a square-wave stimulator.
• The evoked muscle tension was recorded using the force transducer to determine the first muscle twitch tension (T1%) and the ratio of the force of the fourth twitch to the first twitch (T4/T1). This method was used as an indicator of muscle strength and its sustainability.
• Measurements were recorded at 5, 10, 15, 30, and 60 minutes after the intravenous administration of either a vehicle (control substance) or gentamicin at a dosage of 6 mg/kg of body weight.

Results

• The researchers found a significant treatment-time interaction for the effect of gentamicin on the first muscle twitch tension (T1%). This was decreased from 100% to 92% during the 60-minute study period for the vehicle but no such decrease was associated with gentamicin.
• For the T4/T1 ratio, there was not a significant effect of treatment or time or treatment-time interaction between gentamicin and the vehicle. This suggests gentamicin did not impact the muscle’s ability to maintain strength over time.

Conclusions

• The study concluded that a high dose of gentamicin did not cause a decrease in initial muscle strength or impair the muscle’s ability to sustain strength over time.
• The researchers inferred that a single high dose of gentamicin does not cause a significant neuromuscular blockade when administered alone to healthy horses anesthetized with halothane. This could have implications for veterinary practice, as gentamicin is a commonly used antibiotic in many species, including horses. The reassurance that it does not impact neuromuscular function negatively is an important finding.