Interaction of gentamycin and atracurium in anaesthetised horses.

The study investigates the effects of combining the drugs gentamycin and atracurium on the muscle responses of anaesthetised horses. The researchers found that while the combination of these drugs did yield some alterations in muscular responses, overall, the impact was minimal.

Research method

• The research focused on the hind limb digital extensor tension (also referred to as “hoof twitch”) in seven anaesthetised horses. This reflex activity in the horses was maintained at 40% of its baseline for an hour using an infusion of atracurium, an anaesthetic drug commonly used to relax muscles during surgery.
• After the initial hour, the atracurium treatment was stopped, and the hoof twitch was allowed to recover to 75% of its original strength. The process was then repeated, with the second hour of 40% twitch being maintained by another round of atracurium administration.
• During the third hour, gentamycin, an antibiotic, was administered to the horses in addition to the atracurium. The researchers monitored the effect of this drug combination on the hoof twitch reflex.

Findings

• The gentamycin administration led to a reduction in the hoof twitch strength, averaging a decrease from 40% to 29% within approximately seven minutes. The twitch strength eventually re-established itself to its pre-gentamycin strength over the subsequent hour.
• The use of gentamycin alongside atracurium prolonged the recovery time of the hoof twitch from 50% to 75% strength. It took 7.7 minutes for the recovery when atracurium was used alone, and 11.5 minutes when used in combination with gentamycin.
• However, there was no significant difference in the time taken for a ‘fade recovery’ (return of muscle activity after the drug’s effects have worn off) from 50% to 75% twitch – 13.8 minutes with atracurium alone and 13.7 minutes with the drug combination.
• At the 75% recovery of the fade, the hoof twitch strength was 87% with atracurium alone and 82% with the addition of gentamycin.
• The reversal of the muscle block through the use of another drug, edrophonium, and the subsequent recovery of the horses from anaesthesia, were both successful and uneventful.

Conclusion

• Based on these findings, the research concludes that although gentamycin did amplify the neuromuscular blocking effects of atracurium, its overall effect was minor. Thus, the study suggests that the co-administration of these drugs in anaesthetised horses is likely safe, but this practice may need to account for the slightly increased muscle response recovery time when both drugs are used.