Intravenous tramadol: effects, nociceptive properties, and pharmacokinetics in horses.

The study set out to investigate the effectiveness and impacts of tramadol, given intravenously in a range of doses, on horses. Although some side effects were noticed at higher doses, the overall analgesic properties of the medication were not significant under the conditions of this study.

Study Design

• The study was a two-phase, blinded, randomised, prospective crossover study. This means that the experiment was conducted in two distinct parts, those observing and assessing the horses were unaware of the specific treatment given to each horse, and the horses were randomly assigned different doses of tramadol or saline across different periods of the study.
• The research involved seven horses, aged roughly 22.5 years and weighing an average of 565 kg.

Procedures and Measurement

• Different doses of tramadol hydrochloride were administered intravenously every 20 minutes (ranging from 0.1 to 1.6 mg per kg of body weight).
• The investigators made note of a number of physical and behavioural signs thought to indicate the horses’ pain levels both before and up to six hours after treatment.
• Reactions to heat-induced pain were also monitored at specified times following treatment with a standardised 2.0 mg/kg dose of tramadol, or saline.
• Blood samples were taken in order to examine the pharmacokinetics, or how the drug moved through the horses’ system over time.

Results

• Compared with the saline control, tramadol had little effect on some indicators of discomfort or distress, such as heart rate, step frequency, and sweating score.
• Higher doses of tramadol did cause a temporary increase in respiratory rate, head height, and head nodding and trembling, as well as a decrease in intestinal sounds, suggesting some minor side-effects.
• The half-life of tramadol in horses was determined at approximately 2 hours regardless of whether it was given in staggered small doses totalling 3.1 mg/kg, or in one bolus dose of 2.0 mg/kg.
• The thresholds for hoof withdrawal and skin twitching in response to a heat source were not significantly altered by the administration of tramadol, suggesting that it was not an effective painkiller in this context.

Conclusion

• The research concluded that, while doses of tramadol up to 3.1mg/kg brought about some temporary side effects in horses, a bolus dose of 2.0mg/kg did not provide significant pain relief in response to a thermal stimulus.