Pharmacokinetics and pharmacodynamics of dermorphin in the horse.

The research focuses on studying the effects of dermorphin, a mu-opioid receptor binding peptide, in horses. The results suggest that the peptide administered intravenously or intramuscularly, creates both central and peripheral effects on the subjects. The half-life, bioavailability, and excretion of the drug were examined alongside its influence on the horse’s heart rate.

Study Design and Process

• The study included a sample of ten horses which were administered dermorphin either intravenously or intramuscularly.
• The analysis of plasma concentration versus time data was done using compartmental and noncompartmental methods to assess the effectiveness of both modes of dermorphin administration.
• Following administration, urine samples were analyzed to determine the percentage of dermorphin excreted.

Key Findings

• The researchers found that intravenous applications fitted a two-compartment model best, providing distribution and elimination half-lives of approximately 0.09 and 0.76 hours respectively. This indicates that the drug was able to spread quickly within the system and was also eliminated at a relatively fast pace.
• In the case of intramuscular applications, a noncompartmental analysis provided a terminal elimination half-life of around 0.68 hours, which indicates that the elimination of the drug was slower via the muscular route.
• However, bioavailability after intramuscular administration was variable, ranging between 47 and 100 percent. This suggests that not all the administered drug was accessible for use in the body, indicating that intramuscular administration may lead to more inconsistent results.
• The findings show an average of 5.0% of dermorphin was excreted in urine.

Impact of Dermorphin

• Beyond its pharmacokinetic properties, the study also found physiological effects of dermorphin in the horses. Specifically, it led to excitation and an increased heart rate post-intravenous application, which subsided after around 5 minutes.
• A correlation was observed between the plasma concentration of dermorphin and the change in heart rate, fitting a hyperbolic equation, with an EC(50) calculated to be 21.1 ± 8.8 ng/mL. This suggests a dose-response relationship, wherein the effect of the drug increases with its concentration, up to a maximum point.

Detection Period

• Dermorphin was found to be detectable in plasma for 12 hours post-intravenous administration, indicating the time window within which the presence of the drug can be affirmed through a plasma test.
• Similarly, dermorphin was detectable in urine for 48 or 72 hours (depending on the method of administration), showing how long the drug could be traced in urine samples following administration.