Pharmacokinetics and pharmacodynamics of intravenous romifidine and propranolol administered alone or in combination for equine sedation

Comparison of sedation quality and safety of detomidine and romifidine as a continuous rate infusion for standing elective laparoscopic ovariectomy in mares

OBJECTIVE

To compare efficacy and safety of a continuous rate infusion of detomidine hydrochloride and romifidine hydrochloride for standing elective bilateral laparoscopic ovariectomy in mares.

STUDY DESIGN

Blinded, randomized prospective clinical study.

ANIMALS

Eighteen healthy mares presenting for elective bilateral ovariectomy METHODS: Mares were randomly assigned to one of two sedation protocols. Prior to surgery, baseline head height, heart rate, respiratory rate, and postural sway were recorded. An IV loading dose of α2-agonist (46 μg/kg romifidine or 13.9 μg/kg detomidine) was administered. Standing sedation was maintained with a continuous rate infusion of the respective α2-agonist (126 μg/kg/h romifidine or 37.8 μg/kg/h detomidine). Intraoperative measurements included respiratory rate, heart rate, head height, postural sway, and response to surgical stimulus. Postoperatively, fecal output was recorded, and pain scoring was performed using composite pain score and visual analog scales.

RESULTS

Three of 18 horses required additional α-2 agonists: one detomidine and two romifidine and butorphanol. Head height during surgery was lower (p < .001) in mares receiving detomidine. Postural sway around the vertical axis was greater in mares sedated with detomidine rather than romifidine (p = .013). No differences were detected in intraoperative heart rate, postoperative pain scores or postoperative fecal output between sedation techniques.

CONCLUSION

Comparable scores for surgical stimulation and sedation were measured in both sedation groups. No differences in postoperative analgesia or manure production were identified.

CLINICAL SIGNIFICANCE

Romifidine appears suitable as an alternative to detomidine and may limit ataxia and head drop in sedated horses.

Pharmacokinetic-pharmacodynamic modelling of the antinociceptive effect of a romifidine infusion in standing horses

OBJECTIVE

To evaluate the effect of a romifidine infusion on antinociception and sedation, and to investigate its relationship with plasma concentration.

STUDY DESIGN

Prospective, experimental, nonrandomized trial.

ANIMALS

A total of 10 healthy adult warmblood horses.

METHODS

Romifidine (loading dose: 0.08 mg kg^-1, infusion: 0.03 mg kg^-1 hour^-1) was administered intravenously over 120 minutes. Romifidine plasma concentrations were determined by capillary electrophoresis. Sedation quality and nociceptive thresholds were evaluated at regular time points before, during and after romifidine administration. The nociceptive withdrawal reflex was elicited by electrical stimulation at the thoracic limb using a dedicated threshold tracking algorithm and recorded by electromyography at the deltoid muscle. A pharmacokinetic-pharmacodynamic model was established and correlation between romifidine plasma concentration and main output variables tested.

RESULTS

A two compartmental model best described the romifidine pharmacokinetic profile. The nociceptive thresholds increased compared with baseline in all horses from 10 to 146 minutes after romifidine administration (p < 0.001). Peak effect reached 5.7 ± 2.3 times the baseline threshold (mean ± standard deviation). The effect/concentration relationship followed a counter-clockwise hysteresis loop. The mean plasma concentration was weakly correlated to nociceptive thresholds (p < 0.0071, r = 0.392). The sedative effects were significant until 160 minutes but variable, not correlated to plasma concentration (p = 0.067), and weakly correlated to nociceptive thresholds (p < 0.0001, r = 0.33).

CONCLUSIONS AND CLINICAL RELEVANCE

Romifidine elicited a marked antinociceptive effect. Romifidine-induced antinociception appeared with a delayed onset and lasted longer than sedation after discontinuing its administration.

How to score sedation and adjust the administration rate of sedatives in horses: a literature review and introduction of the Ghent Sedation Algorithm

OBJECTIVE

To summarize the different methods used to assess sedation and/or adjust the dose or administration rate of alpha-2 agonists in horses and to propose an algorithm to adjust the administration rate of a constant rate infusion of an alpha-2 agonist in horses.

DATABASES USED

PubMed and Web of Science; search terms: horse, sedation and score.

CONCLUSIONS

Most authors distinguish between sedation depth, sedation quality and degree of ataxia. These three features are evaluated using scoring systems similar to those classically used to assess pain, i.e. simple descriptive scales, numerical rating scales (NRS), visual analogue scales and/or multifactorial sedation scales. In addition, head height above the ground is often used as a measure of the depth of sedation. Very few authors have described how to adjust the administration rate or dose of alpha-2 agonists. Based on the available literature, the Ghent Sedation Algorithm was developed, which assigns scores (NRS) for degree of ataxia, sedation depth and surgical conditions, and uses these to prescribe changes in the administration rate of constant rate infusions of alpha-2 agonists. Studies are needed to validate this algorithm.

Pharmacokinetics and selected pharmacodynamics of romifidine following low-dose intravenous administration in combination with exercise to quarter horses

Romifidine is an alpha-2 adrenergic agonist used for sedation and analgesia in horses. As it is a prohibited substance, its purported use at low doses in performance horses necessitates further study. The primary goal of the study reported here was to describe the serum concentrations and pharmacokinetics of romifidine following low-dose administration immediately prior to exercise, utilizing a highly sensitive liquid chromatography-tandem mass spectrometry assay that is currently employed in many drug testing laboratories. An additional objective was to describe changes in heart rate and rhythm following intravenous administration of romifidine followed by exercise. Eight adult Quarter Horses received a single intravenous dose of 5 mg (0.01 mg/kg) romifidine followed by 1 h of exercise. Blood samples were collected and drug concentrations measured at time 0 and at various times up to 72 h. Mean ± SD systemic clearance, steady-state volume of distribution and terminal elimination half-life were 34.1 ± 6.06 mL/min/kg and 4.89 ± 1.31 L/kg and 3.09 ± 1.18 h, respectively. Romifidine serum concentrations fell below the LOQ (0.01 ng/mL) and the LOD (0.005 ng/mL) by 24 h postadministration. Heart rate and rhythm appeared unaffected when a low dose of romifidine was administered immediately prior to exercise.