Pharmacokinetics and pharmacodynamics comparison between subcutaneous and intravenous butorphanol administration in horses.

This research investigates the differences in drug absorption and effects between injecting butorphanol subcutaneously (under the skin) and intravenously (into the vein) in horses. The results showed that subcutaneous administration allows the drug to maintain effective blood concentration for longer, with less impact on behavior and physiology compared to intravenous injection, presenting it as a viable alternative method of drug delivery in horses.

Study Design and Procedure

• The goal of the study was to examine how butorphanol, a pain-relieving medication, is absorbed and processed by the body when it’s administered via two different routes – intravenously and subcutaneously – in horses.
• Using a randomized crossover design, ten adult horses received 0.1 mg/kg of butorphanol either via an intravenous injection directly into the vein or a subcutaneous injection beneath the skin.
• The levels of butorphanol in the blood were measured at predetermined times using a precise scientific method called liquid chromatography-tandem mass spectrometry (LC-MS/MS).
• The demeanor, or behavior, of the horses and physiological parameters were also recorded during the study.
• Data were statistically analyzed using a multivariate mixed-effect model on ranks.

Key Findings

• The findings reveal that the absorption half-life and peak plasma concentration of butorphanol after a subcutaneous injection were relatively short and stable.
• Subcutaneously administered butorphanol had a bioavailability of 87%, showing that a significant proportion of the drug was effectively absorbed into the body.
• After intravenous injection, the butorphanol steady-state volume of distribution and clearance, which represent the drug’s dispersion and elimination from the body respectively, were noted.
• The terminal half-life for butorphanol, which represents how long the drug takes to reduce to half its initial concentration, was longer for subcutaneous administration than for intravenous administration.
• The plasma levels of butorphanol remained above therapeutical concentration for a longer time with subcutaneous administration compared to intravenous administration, showing its capability for extended relief.
• The physiological and behavioral effects of the drug were also less pronounced with subcutaneous injection.

Conclusions

• Based on these findings, it was concluded that subcutaneous administration of butorphanol was a suitable alternative to intravenous administration in adult horses.
• The less marked physiological and behavioral effects combined with superior sustained therapeutic plasma levels highlight the potential advantages of subcutaneous administration.