Alfaxalone for total intravenous anaesthesia in horses

Published:October 27, 2018DOI:



      To determine the suitability of alfaxalone total intravenous (IV) anaesthesia in horses and concurrently evaluate infusion rates, cardiovascular effects, pharmacokinetics and the quality of the anaesthetic recovery period.

      Study design

      Prospective, experimental study.


      Eight Standardbred horses.


      Horses were premedicated with IV acepromazine (0.03 mg kg–1) and xylazine (1 mg kg–1) and anaesthesia was induced with guaifenesin (35 mg kg–1) and alfaxalone (1 mg kg–1). Anaesthesia was maintained for 180 minutes using an IV infusion of alfaxalone at a rate determined by a horse’s response to a supramaximal electrical noxious stimulus. Venous blood samples were regularly collected to determine alfaxalone plasma concentrations and for pharmacokinetic analysis. Cardiopulmonary variables were monitored and the quality of the anaesthetic recovery period scored.


      The median (range) alfaxalone infusion rate was 3.1 (2.4–4.3) mg kg–1 hour–1. The mean ± standard deviation plasma elimination half-life, plasma clearance and volume of distribution for alfaxalone were 41 minutes, 25 ± 6.3 mL minute–1 kg–1 and 1.6 ± 0.5 L kg–1, respectively. During anaesthesia, mean arterial blood pressure was maintained above 70 mmHg in all horses. Cardiac index reached a minimum value (68% of baseline values) immediately after induction of anaesthesia and was maintained between 74% and 90% of baseline values for the remainder of the anaesthetic protocol. Following the cessation of the alfaxalone infusion, six of eight horses exhibited muscle tremors and paddling. All horses stood without incident on the first or second attempt with a median recovery score of 4.5 (good to excellent).

      Conclusions and clinical relevance

      Anaesthesia in horses can be maintained with an infusion of alfaxalone at approximately 3 mg kg–1 hour–1. The alfaxalone infusion rates used resulted in minimal haemodynamic changes and good recovery quality. Mean alfaxalone plasma concentration was stable over the infusion period and clearance rates were similar to previously published single-dose alfaxalone studies in horses.


      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Veterinary Anaesthesia and Analgesia
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Ambros B.
        • Duke-Novakovski T.
        • Pasloske K.S.
        Comparison of the anesthetic efficacy and cardiopulmonary effects of continuous rate infusions of alfaxalone-2-hydroxypropyl-beta-cyclodextrin and propofol in dogs.
        Am J Vet Res. 2008; 69: 1391-1398
        • Aoki M.
        • Wakuno A.
        • Kushiro A.
        • et al.
        Evaluation of total intravenous anesthesia with propofol-guaifenesin-medetomidine and alfaxalone-guaifenesin-medetomidine in Thoroughbred horses undergoing castration.
        J Vet Med Sci. 2017; 79: 2011-2018
        • Deutsch J.
        • Ekiri A.
        • de Vries A.
        Alfaxalone for maintenance of anaesthesia in ponies undergoing field castration: continuous infusion compared with intravenous boluses.
        Vet Anaesth Analg. 2017; 44: 832-840
        • Duke T.
        • Filzek U.
        • Read M.
        • et al.
        Clinical observations surrounding an increased incidence of postanesthetic myopathy in halothane-anesthetized horses.
        Vet Anaesth Analg. 2006; 33: 122-127
        • Gibaldi M.
        • Perrier D.
        Estimation of areas.
        in: Pharmacokinetics. Marcel and Decker, Basel1982: 445-449
        • Goodwin W.
        Studies of alfaxalone in horses.
        (PhD Thesis) University of Queensland, 2013: 123-131
        • Goodwin W.
        • Keates H.
        • Pasloske K.
        • et al.
        Plasma pharmacokinetics and pharmacodynamics of alfaxalone in neonatal foals after an intravenous bolus of alfaxalone following premedication with butorphanol tartrate.
        Vet Anaesth Analg. 2012; 39: 503-510
        • Goodwin W.A.
        • Keates H.L.
        • Pasloske K.
        • et al.
        The pharmacokinetics and pharmacodynamics of the injectable anaesthetic alfaxalone in the horse.
        Vet Anaesth Analg. 2011; 38: 431-438
        • Goodwin W.A.
        • Keates H.L.
        • Pearson M.
        • et al.
        Alfaxalone and medetomidine intravenous infusion to maintain anaesthesia in colts undergoing field castration.
        Equine Vet J. 2013; 45: 315-319
        • Granados M.M.
        • Dominguez J.M.
        • Fernández-Sarmiento A.
        • et al.
        Anaesthetic and cardiorespiratory effects of a constant-rate infusion of alfaxalone in desflurane-anaesthetised sheep.
        Vet Rec. 2012; 171: 125-131
        • Hodgson D.S.
        • Steffey E.P.
        • Grandy J.L.
        • et al.
        Effects of spontaneous, assisted, and controlled ventilatory modes in halothane-anesthetized geldings.
        Am J Vet Res. 1986; 47: 992-996
        • Keates H.
        • Whittem T.
        Effect of intravenous dose escalation with alfaxalone and propofol on occurrence of apnoea in the dog.
        Res Vet Sci. 2012; 93: 904-906
        • Kloppel H.
        • Leece E.A.
        Comparison of ketamine and alfaxalone for induction and maintenance of anaesthesia in ponies undergoing castration.
        Vet Anaesth Analg. 2011; 38: 37-43
        • Lau C.
        The safety, efficacy and neuromotor effects of the neurosteroid anaesthetic alfaxalone in rats.
        (PhD Thesis) The University of Queensland, 2013: 93-123
        • Leece E.A.
        • Girard N.M.
        • Maddern K.
        Alfaxalone in cyclodextrin for induction and maintenance of anaesthesia in ponies undergoing field castration.
        Vet Anaesth Analg. 2009; 36: 480-484
        • Muir W.W.
        • Lerche P.
        • Wiese A.
        • et al.
        Cardiorespiratory and anaesthetic effects of clinical and supraclinical doses of alfaxalone in dogs.
        Vet Anaesth Analg. 2008; 35: 451-462
        • Muir W.W.
        • Lerche P.
        • Wiese A.
        • et al.
        The cardiorespiratory and anaesthetic effects of clinical and supraclinical doses of alfaxalone in cats.
        Vet Anaesth Analg. 2009; 36: 42-54
        • Ndawana P.S.
        • Dzikiti B.T.
        • Zeiler G.
        • et al.
        Determination of the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to a standardised noxious stimulus in goats.
        Vet Anaesth Analg. 2015; 42: 65-71
        • Nyman G.
        • Funkquist B.
        • Kvart C.
        Atelectasis causes gas exchange impairment in the anaesthetized horse.
        Equine Vet J. 1990; 22: 317-324
        • Nyman G.
        • Hedenstierna G.
        Ventilation-perfusion relationships in the anaesthetized horse.
        Equine Vet J. 1989; 21: 274-281
        • Ohmura H.
        • Okano A.
        • Mukai K.
        • et al.
        Cardiorespiratory and anesthetic effects of combined alfaxalone, butorphanol, and medetomidine in Thoroughbred horses.
        J Equine Sci. 2016; 27: 7-11
        • Prys-Roberts C.
        Practical and pharmacological implications of continuous intravenous anaesthesia.
        Acta Anaesthesiol Belg. 1980; 31: 225-230
        • Pypendop B.H.
        • Ranasinghe M.G.
        • Pasloske K.
        Pharmacokinetics of alfaxalone infusions, context-sensitive half-time and recovery times in male neutered cats.
        Vet Anaesth Analg. 2018; 45: 630-639
        • Scharzwald C.
        • Bonagura J.D.
        • Muir III, W.W.
        The cardiovascular system.
        in: Muir III, W.W. Hubbell J.A. Equine Anesthesia: Monitoring and Emergency Therapy. 2nd edn. Elsevier, USA2009: 49
        • Schwarz A.
        • Kalchofner K.
        • Palm J.
        • et al.
        Minimum infusion rate of alfaxalone for total intravenous anaesthesia after sedation with acepromazine or medetomidine in cats undergoing ovariohysterectomy.
        Vet Anaesth Analg. 2014; 41: 480-490
        • Wagner A.E.
        • Bednarski R.M.
        • Muir III, W.W.
        Hemodynamic effects of carbon dioxide during intermittent positive-pressure ventilation in horses.
        Am J Vet Res. 1990; 51: 1922-1929
        • Yamashita K.
        • Tsubakishita S.
        • Futaoka S.
        • et al.
        Cardiovascular effects of medetomidine, detomidine, and xylazine in horses.
        J Vet Med Sci. 2000; 62: 1025-1032