Plasma concentrations, analgesic and physiological assessments in horses with chronic laminitis treated with two doses of oral tramadol.

The research study was intended to examine the effects of varying doses of the oral drug tramadol on horses suffering from chronic laminitis, a painful condition. The trial aimed to observe plasma concentrations and measure the physical and analgesic effects of the treatment.

Methodology

• The study was a non-randomised trial using four horses with naturally occurring chronic laminitis.
• Two doses of tramadol were given orally to each horse: 5 mg/kg body weight (bwt), and then 10 mg/kg bwt, each dose repeated every 12 hours for a week.
• There was a one-week washout period between the two treatment regimens, where no medication was given, to ensure that any effects were due to the treatment being studied and not to residual effects of the previous treatment.
• Several physical parameters were evaluated both before and during the treatment, including arterial blood pressure, heart and respiratory rates, intestinal sounds, and frequency of forelimb off-loading.
• Plasma concentrations of tramadol and its metabolites (M1 and M2) were measured at predetermined times and dates following the morning dose.

Results

• The frequency of forelimb off-loading reduced significantly by 40% with the 10 mg/kg bw treatment, while there was only a 9% reduction with the 5 mg/kg bwt treatment.
• No significant changes were observed in the physiological variables measured, such as pulse and respiration rates, blood pressure, and intestinal sounds, with either treatment dose.
• For both the 5 mg/kg bw and 10 mg/kg bw treatments, observed peak plasma concentrations of the drug and its metabolites fell within certain ranges: tramadol – 329 to 728 μg/l and 628 to 1330 μg/l; M1 – 12-24 μg/l and 32-80 μg/l; and M2 – 90-157 μg/l and 239-362 μg/l, respectively.
• Median areas under the concentration vs. time curves for the two treatments were 727 h μg/l and 1426 h μg/l (for tramadol), 33 h μg/l and 88 h μg/l (for M1), and 303 h μg/l and 1003 h μg/l (for M2).

Conclusion

• Administering oral tramadol twice daily at a dose of 10 mg/kg bwt may lead to analgesic plasma levels in horses suffering from chronic laminitis.