Pharmacokinetics and pharmacodynamics of tramadol in horses following oral administration.

The research investigates the effects of differing doses of tramadol, a synthetic opioid, on horses. The study aims to deepen understanding of the drug’s pharmacokinetics, which is how a drug moves through the body, and its pharmacodynamics, or how it affects the body.

Research Methodology

The research involved nine healthy adult horses which received one of three doses (3, 6, and 9 mg/kg) of tramadol, orally via a nasogastric tube. The study focused on two substances: tramadol itself and its active metabolite known as M1.

• Blood samples from the horses were collected at several time points, starting from time zero (when the drug was administered), and up to 96 hours post-administration.
• Urine samples were also collected up to 120 hours after administration.
• The samples’ plasma and urine were examined using liquid chromatography-mass spectrometry, a technique commonly used to analyze organic compounds.
• The gathered data from these tests was processed using noncompartmental analysis, a mathematical approach aimed at deriving useful information from drug concentration time data.

Research Findings

Key parameters of pharmacokinetics were reported for the 3, 6, and 9 mg/kg dosage groups which included maximum concentration (Cmax), time to reach maximum concentration (Tmax), and half-life (t1/2λ).

• For the mentioned dosages, the Cmax values were 43.1, 90.7, and 218 ng/mL, respectively. Tmax was noted to be 0.750, 2.0, and 1.5 hours, and t1/2λ was around 2.14, 2.25, and 2.39 hours.
• The study revealed that tramadol and its active metabolite M1 were present in plasma concentrations within the analgesic range for humans in the 3 and 6 mg/kg dose groups. However, the concentrations were at the lower end of this range and were maintained only for a short time.

Conclusion and Recommendations

The research makes it clear there’s a need for establishing effective analgesic plasma concentration in horses as the levels reached in this study were at the lower end and short-lived. Therefore, the study advises that prescriptions of tramadol for pain control in horses should be made cautiously. Despite variations in dose levels, no significant negative behavioral or physiological effects were observed in any of the horses.