Plasma concentrations, behavioural and physiological effects following intravenous and intramuscular detomidine in horses.

This research focuses on the relationship between plasma concentrations of the drug detomidine hydrochloride in horses and its physiological and behavioural effects when administered either intravenously (i.v.) or intramuscularly (i.m.). The study found that effects were positively influenced by the plasma drug concentration, which varied based on the administration route, therefore impacting the drug’s desired and undesirable effects.

Methods and Objectives

• The study aimed to expand existing research on detomidine, a drug used to sedate horses, by assessing its effects when administered through i.v. and i.m. routes. In so doing, the researchers aimed to build a correlation between plasma drug concentrations and their systemic effects.
• The researchers studied the behavioural (like head position) and physiological (like heart rate) responses of 8 horses after the administration of detomidine. The study followed a balanced crossover design; thus, each horse experienced both i.v. and i.m. administration at different times.
• Blood samples at predetermined intervals (from 0.5 min to 48 h post-administration) were collected for subsequent detomidine concentration measurements using liquid chromatography-mass spectrometry.

Results

• The plasma concentration of detomidine peaked earlier and was significantly higher with i.v. administration compared to i.m. administration.
• The physiological and behavioural changes were more significant and observed at earlier time points for the i.v. group compared to the i.m. group. For instance, the average head position across both groups dropped to about 35 cm from the ground 10 min after i.v. administration, while it decreased to about 64 cm after 60 min of i.m. administration.
• The heart rate showed a similar pattern, with a lower value of 17 beats/min 10 min following i.v. administration, and 29 beats/min 30 min after i.m. administration.

Conclusions

• The results showed a positive correlation between the detomidine plasma concentration and the effects measured, which varied based on the route of administration. This finding is critical because the plasma concentration affects the desirable and undesirable effects of the drug, thereby impacting case management.