Pharmacokinetics and pharmacodynamics of meperidine after intramuscular and subcutaneous administration in horses

Pharmacokinetics of dexmedetomidine in anaesthetized horses following repeated subcutaneous administration and intravenous constant rate infusion

BACKGROUND

The inclusion of dexmedetomidine (DEX) within a balanced general anaesthesia protocol is effective in improving the clinical outcome and recovery quality of anaesthesia in horses. This study aimed to determine the pharmacokinetic profile of DEX following repeated subcutaneous (SC) administration at 2 µg/kg every 60 min till the end of the procedure in comparison to intravenous constant rate infusion (CRI) at 1 µg/kg/h in anaesthetized horses undergoing diagnostic procedures up to the end of the diagnostic procedure.

RESULTS

In the CRI and SC groups DEX maximum concentrations (Cmax) were 0.83 ± 0.27 ng/mL and 1.14 ± 0.71 ng/mL, respectively, reached at a time (Tmax) of 57.0 ± 13.4 min and 105.5 ± 29.9 min. Mean residence time to the last measurable concentration (MRTlast) was 11.7 ± 6.2 and 55.8 ± 19.7 min for the CRI group and SC groups, respectively. The apparent elimination half-life was 18.0 ± 10.0 min in the CRI group and 94.8 ± 69.8 min for the SC group, whereas the area under the curve (AUC0-last) resulted 67.7 ± 29.3 and 83.2 ± 60.5 min*ng/mL for CRI and SC group, respectively. Clearance was 16.26 ± 8.07 mL/min/kg for the CRI group. No signs of adverse effects were recorded in both groups.

CONCLUSIONS

The pharmacokinetic profile of DEX following repeated SC administration in anaesthetized horses was comparable to intravenous CRI administration during the intranaesthetic period and beneficial during the recovery phase from general anaesthesia. The SC route could be considered as an alternative to CRI for improving the recovery quality of equine patients undergoing general anaesthesia.

Accelerometric Evaluation of the Locomotor Pattern After Administration of Morphine in Conscious Healthy Horses

The objective of the present study was to compare, using accelerometry, the gait changes produced after administration of a dose of 0.2 mg/kg of morphine at the walk in healthy horses. Six mature horses were used, and all animals received two different treatments with, at least, two weeks interval in between. Treatments administered consisted of a single dose of 10 ml of saline solution or a total of 0.2 mg/kg of morphine diluted in 10 ml of saline solution. A three-dimensional accelerometric device was used to collect data continuously while horses were walking. The walking test was performed 10 min prior to injection, and then at 5, 10, 15 and 20 min after injection and then every 10 min for 3 h. Eight variables were calculated including stride kinematic, coordination and energetic parameters. Additionally, the force of acceleration and three components of the power were calculated. Significant interaction was only observed for stride length, propulsion power and the propulsive part of the total power with a reduction in values after morphine administration. Compared to baseline values, stride length values were significantly reduced for 80 min and again 110 min after injection of the opioid and at 5, 15, 20, 30 and 40 min in the case of propulsion power values. For the propulsion component of power, these differences were observed for 20 min when compared to baseline values. The administration of 0.2 mg/kg of morphine to conscious healthy horses produces limited effects on the gait pattern of horses and the effects on locomotor activity are minimal at this dose, not being an important concern for the administration of analgesia in a clinical setting.