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Clinical pharmacokinetics and pharmacodynamics of intravenous alfaxalone in young Thoroughbred horses premedicated with medetomidine and midazolam
Author(s) -
Wakuno Ai,
Aoki Motoki,
Kushiro Asuka,
Mae Naomi,
Maeda Tatsuya,
Yamazaki Yosuke,
Minamijima Yohei,
Nagata Shunichi,
Ohta Minoru
Publication year - 2019
Publication title -
veterinary record
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.261
H-Index - 99
eISSN - 2042-7670
pISSN - 0042-4900
DOI - 10.1136/vr.105070
Subject(s) - medetomidine , pharmacokinetics , midazolam , medicine , volume of distribution , anesthesia , premedication , pharmacodynamics , horse , pharmacology , heart rate , sedation , blood pressure , paleontology , biology
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.