Abstract
The aims of this study were to assess the plasma concentrations of romifidine in horses after intravenous injection, to evaluate the red blood cell (RBC) partitioning of the anaesthetic drug, and to improve knowledge regarding its sedative effect in horses describing the pharmacokinetic model. Eight adult Standardbred horses received a single bolus of romifidine at a dosage of 100 μg/kg. Blood samples (5 mL) were collected immediately before romifidine administration (t 0), and at 2, 5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 90, 105, 120, 150 and 180 min after injection. A sedation score was recorded at the same time. The romifidine concentrations in plasma and red blood cells were determined by high performance liquid chromatography (HPLC). The plasma and red blood cell concentrations were correlated with the sedation at each time point. Romifidine produced a satisfactory level of sedation in all animals. The sedation was detectable in all horses for up to 105 min. All the animals returned to normal without any behavioural changes at 180 min. The romifidine concentrations in the red blood cells were significantly higher (P < 0.01) at all time points than those in the plasma. The T1/2β was 148.67 ± 61.59 min and body clearance was 22.55 ± 6.67 mL/kg per min. The results showed that after a single bolus administration of romifidine, a partitioning in the RBCs was detected.
Highlights
The use of alpha-2 adrenoceptor agonist drugs has gained wide acceptance in equine veterinary practice (Marzok et al 2014)
The results showed that the release of romifidine from red blood cell (RBC) to plasma was consistent and continuous during the entire sedation period (Fig. 1)
After IV administration, the RBC concentrations of romifidine were approximately two time higher than those detected in plasma
Summary
The use of alpha-2 adrenoceptor agonist drugs has gained wide acceptance in equine veterinary practice (Marzok et al 2014). Detomidine and romifidine have currently been approved for use in Europe 1950/2006) and are used for purposes of sedation, analgesia and premedication (England & Clarke 1996; Gozalo-Marcilla et al 2015). Romifidine [N-(2-bromo-6-fluoro-phenyl)-4,5dihydro-1H-imidazol-2-amine mono-hydrochloride, C9H9BrFN3], is commonly administered intravenously to produce sedation and provide analgesia in horses. Similar to other alpha-2 agonists, the side effects related to the administration of romifidine are bradycardia, arrhythmias, decreased cardiac output and increased systemic vascular resistance, respiratory depression, transient decreases in arterial partial pressure of oxygen and ataxia (Wojtasiak-Wypart et al 2012; Gozalo-Marcilla et al 2015). When compared with IV xylazine (1 mg/kg) or detomidine (20 lg/kg), romifidine at 40 and 80 lg/kg produced less ataxia and the horses’ heads were held higher; the duration of these effects was longer than the others. The lack of ataxia with romifidine has made it very popular for sedating horses in standing
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