title: Pharmacokinetics and selected pharmacodynamics of romifidine following low-dose intravenous administration in combination with exercise to quarter horses.
abstract: 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.
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.|Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors.forename: H K
authors.initials: HK
authors.lastname: Knych
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.|Department of Veterinary Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Stanley
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors.forename: D S
authors.initials: DS
authors.lastname: McKemie
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Steinmetz
mesh_terms: D061605:Administration, Intravenous / Q000662:veterinary*; D058647:Adrenergic alpha-2 Receptor Agonists / Q000493:pharmacokinetics*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate; D006736:Horses / Q000378:metabolism*; D007093:Imidazoles / Q000493:pharmacokinetics*; D007275:Injections, Intravenous; D010805:Physical Conditioning, Animal / Q000502:physiology*
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D007093:Imidazoles; C076257:romifidine