Preliminary pharmacokinetics of morphine and its major metabolites following intravenous administration of four doses to horses.

The article presents an investigation into how horses react to different doses of morphine delivered intravenously, concentrating on observing pharmacokinetics, behavior, and gastrointestinal interaction.

Study Design and Procedure

• The research was structured around administering a one-off dose of morphine to horses. The doses affected were 0.05, 0.1, 0.2, and 0.5 mg/kg. The morphine was delivered intravenously, with two horses in each dose group, culminating in a total of eight participant horses.
• In order to determine the reactions and aftereffects of the morphine, the investigators conducted various tests for up to 72 hours post-drug administration. These tests included taking blood samples, analyzing them with Liquid Chromatography-Mass Spectrometry/Mass Spectrometry (LC-MS/MS), and determining pharmacokinetic parameters.

Results and Findings

• The half-life of morphine was found to swing between 0.675 to 2.09 hours and 6.70 to 18.1 hours for the beta and gamma phase, correspondingly, after the administration of the varying intravenous doses.
• The volume of distribution at a steady pace and the systemic clearance rate ranged between 6.95 to 15.8 L/kg and 28.3 to 35.7 mL · min/kg respectively.
• Effects on behavior and gastrointestinal activity were also recorded—the only metabolites identified in the blood samples were morphine-3-glucuronide and morphine-6-glucuronide, the principal metabolites found in other species. Muscle contractions were seen at dosages of 0.2 and 0.5 mg/kg, with unsteady movements cited at 0.5 mg/kg.
• In all dose groups, gastrointestinal activity dropped (for up to 8 hours in 7 out of 8 horses, and 24 hours in one horse).
• Plasma concentrations of morphine-3-glucuronide, a metabolite known for its neuro-excitatory activity in mice, overshot that of morphine-6-glucuronide remarkably.

Conclusions and Future Research

• This study builds on previous research and is the maiden report describing the metabolites of morphine in horses. The investigators suggest that the high doses of morphine-3-glucuronide may contribute to the dose-dependent excitation observed at higher morphine doses. Further probing into this area is recommended to borrow understanding and insight from such study which may end up having broader implications.