Intravenous and sublingual buprenorphine in horses: pharmacokinetics and influence of sampling site.

This study investigates the pharmacokinetics, possible side effects, and the effect of sampling site on plasma concentrations of buprenorphine administered intravenously and sublingually to horses.

Methodology

• The research involved a randomized crossover experiment with a prospective study. Eleven healthy adult horses between 6 and 20 years of age and weighing 487-592 kg were used for the study.
• In the first phase, buprenorphine was administered once either intravenously or sublingually at a dosage rate of 0.006 mg kg(-1) and pharmacokinetic parameters were then determined for each administration route using noncompartmental modeling.
• Later, in the second phase, the jugular and lateral thoracic veins were simultaneously catheterized for simultaneous venous blood sample collection following a sublingual buprenorphine dose of 0.006 mg kg(-1).
• Plasma buprenorphine concentrations for both phases were measured utilizing ultra-performance liquid chromatography coupled with mass spectrometry. The horses were also monitored for signs of behavioral excitement and changes in gastrointestinal motility at each sample collection period.

Results

• The study reported an average half-life of 5.79 ± 1.09 hours for intravenous buprenorphine administration in horses. The systemic clearance rate after intravenous administration was found to be 6.13 ± 0.86 mL kg(-1) minute(-1), and the volume distribution at steady-state was reported as 3.16 ± 0.65 L kg(-1).
• Evidence of behavioral excitement was observed in horses following intravenous administration of buprenorphine. Both routes of administration led to a decrease in gastrointestinal sounds; however, no signs of colic were reported in any of the horses.
• A noteworthy discrepancy was reported in plasma buprenorphine concentrations when measured in the jugular vein compared to the lateral thoracic vein after the second phase of the study. Unfortunately, due to this discrepancy, pharmacokinetic parameters following sublingual buprenorphine are not reported.

Conclusions

• Buprenorphine, per the findings of this study, demonstrated a long plasma half-life and generated plasma concentrations that appeared consistent with producing an analgesic effect in other species for a duration of up to 4 hours following intravenous administration of this dosage in horses
• It was established that buprenorphine is absorbed into the circulation following sublingual administration. Still, the study warns against using jugular venous sampling for measuring the quantity absorbed, as it was shown to provide a misleading measurement of the sublingual administration uptake.