Letter: Collapse following intravenous administration of oxytetracycline in two horses.

This research letter describes two cases of adverse reactions in horses following the intravenous administration of the antibiotic oxytetracycline hydrochloride, though other horses treated with the same medication did not exhibit the same response, indicating a possible individual hypersensitivity.

Case Study Observations

• The report discusses two particular cases; a three-year-old thoroughbred gelding with an infected leg injury and a 21-year-old pony suffering from chronic bronchopneumonia. Both horses underwent similar negative reactions upon receiving the drug oxytetracycline hydrochloride intravenously.
• Reactions included immediate physical discomfort, evidenced by shivering, staggering, falling and fast paddling movements of the legs, laborious respiration, a rapid heart rate, deep red mucous membranes, profuse sweating, and an increased rectal temperature. With the thoroughbred, recovery took six days; with the pony, recovery was more rapid and occurred within minutes.
• Emergency treatment was administered to both horses, involving the intramuscular injection of tripelennamine, adrenaline tartrate, and prednisolone trimethyl acetate.

Oxytetracycline Hydrochloride Administration

• The same multidosc container of oxytetracycline hydrochloride was used for both horses, raising questions about the consistency of the drug.
• However, the authors note that several other horses were treated with oxytetracycline hydrochloride from the same container in between these two cases, and they did not experience the same adverse effects.
• This information suggests the reactions may not be due to a defect in the drug, but rather to individual physiological responses in the affected horses.
• The rate of administration of the drug was rapid but not faster than what the author usually employs, reducing the likelihood that the rate of injection caused the reaction.

Implications and Interpretations

• Although it’s clear that the two horses had adverse reactions to oxytetracycline hydrochloride, the other horses’ normal responses to the same batch of the drug suggest that the problem might not be with the drug itself.
• The apparent individualised hypersensitivity to this drug in the two horses suggests that veterinarians should be cautious and monitor their patients carefully when administering oxytetracycline hydrochloride for the first time.
• Further studies are needed to understand why some animals may have adverse reactions to this drug.