Influence of induced hypermagnesemia and hypocalcemia on neuromuscular blocking property of oxytetracycline in the horse.

This research article investigates the neuromuscular blocking effects of the antibiotic oxytetracycline in horses under varying levels of magnesium and calcium in the body, concluding that the antibiotic’s potential for neuromuscular blocking is not a significant factor in adverse reactions in horses.

Research methodology

• The researchers used anesthetized horses for their study, particularly focusing on the neurally evoked contractile response of the muscles in the upper lip.
• The antibiotic oxytetracycline was administered intravenously, at a total dose rate of 21 to 28 mg/kg. This dosage did not alter the contractile response of the muscles in the upper lip.
• Additionally, the arterial blood pressure of the horses was not affected by these dose rates.

Neuromuscular blocking property of oxytetracycline

• The neuromuscular blocking effect of oxytetracycline surfaced when the antibiotic was introduced during a partial neuromuscular blockade which was induced by infusion of magnesium sulfate (0.12 or 0.16 g/kg).
• However, moderate hypocalcemia, induced by infusion of sodium oxalate, did not enhance the neuromuscular blocking ability of the antibiotic.

Role of calcium concentration and conclusions

• Considering that the dose rates of the oxytetracycline preparation had a marginal effect on the calcium concentration of equine serum (less than 0.3 mg/dl), the researchers inferred that calcium binding may not play a significant role in the neuromuscular blocking effect of oxytetracycline.
• On concluding their study, the researchers stated that the weak neuromuscular blocking effect of oxytetracycline does not comprise a significant cause in the acute type of adverse reaction to this antibiotic that is occasionally encountered in horses.