Clinical pharmacokinetics and pharmacodynamics of intravenous alfaxalone in young Thoroughbred horses premedicated with medetomidine and midazolam. (30th March 2019)

• Record Type: Journal Article
• Authors: Wakuno, Ai; Aoki, Motoki; Kushiro, Asuka; Mae, Naomi; Maeda, Tatsuya; Yamazaki, Yosuke; Minamijima, Yohei; Nagata, Shun‐ichi; Ohta, Minoru
• Is Part Of: Veterinary record. Volume 184:Number 13(2019)
• Page Start: 411
• Page End: 411
• Publication Date: 2019-03-30
• Subjects: alfaxalone -- pharmacokinetics -- pharmacodynamics -- Thoroughbred -- horse; Veterinary medicine -- Periodicals; Médecine vétérinaire -- Périodiques; Veterinary medicine; Veterinary Medicine; Periodicals; Periodical; Electronic journals; 636.089
• DOI: 10.1136/vr.105070
• Languages: English
• ISSNs: 0042-4900

Abstract

Abstract : To investigate the clinical pharmacokinetics and pharmacodynamics of intravenous alfaxalone in young Thoroughbred horses, seven Thoroughbred horses were randomly anaesthetised twice with either 1 or 2 mg/kg of intravenous alfaxalone after premedication with medetomidine (6 µg/kg intravenous) and midazolam (20 µg/kg intravenous). Blood samples were collected at predetermined time points up to two hours after administration. Plasma alfaxalone concentrations were quantified by a liquid chromatography tandem‐mass spectrometry method and analysed by non‐compartmental pharmacokinetic analysis. Induction and recovery qualities were good to excellent for both doses. Recovery time for the 2 mg/kg (median 90 minutes) was significantly longer than that for the 1 mg/kg (median 50 minutes). Respiratory rate for the 2 mg/kg was significantly lower than that for the 1 mg/kg, resulting in hypoxaemia. The median (range) elimination half‐life, total clearance and volume of distribution were 58.2 (42.3–70.7) minutes, 11.6 (10.3–14.5) ml/minute/kg and 0.8 (0.7–0.9) l/kg for the 1 mg/kg and 59.8 (47.5–68.0) minutes, 14.7 (12.1–16.0) ml/minute/kg and 0.9 (0.9–1.2) l/kg for the 2 mg/kg, respectively. Alfaxalone is rapidly eliminated from the plasma in young Thoroughbred horses. Respiratory depression should be especially noted when alfaxalone is used in clinical practice.