Comparison of alfaxalone, ketamine and thiopental for anaesthetic induction and recovery in Thoroughbred horses premedicated with medetomidine and midazolam.
Authors: Wakuno A, Aoki M, Kushiro A, Mae N, Kodaira K, Maeda T, Yamazaki Y, Ohta M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Anaesthetic Induction Agents in Thoroughbreds Alfaxalone represents a relatively novel injectable anaesthetic option for equine practice, yet comparative evidence in Thoroughbreds remains sparse. Wakuno et al. (2017) evaluated how alfaxalone, ketamine and thiopental performed as induction agents in six Thoroughbreds premedicated with medetomidine and midazolam, using a randomised crossover design and scoring induction and recovery quality alongside continuous cardiopulmonary monitoring. All three agents produced comparable induction quality and cardiovascular stability, though induction speed differed: ketamine took significantly longer (67 seconds) compared with alfaxalone (49 seconds) and thiopental (48 seconds). The critical practical distinction emerged in recovery—ketamine facilitated rapid standing (25 minutes) whereas alfaxalone and thiopental prolonged this phase to approximately 40–44 minutes, a meaningful consideration for equine anaesthetic protocols where extended recovery carries increased injury risk. These findings suggest alfaxalone is a viable alternative to thiopental with similar haemodynamic safety, though practitioners should counsel clients that alfaxalone cases will require extended recovery periods comparable to barbiturate anaesthesia rather than the speedier ketamine-based recoveries.
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Practical Takeaways
- •When rapid induction is required in Thoroughbreds premedicated with medetomidine and midazolam, alfaxalone and thiopental are preferable to ketamine as they induce anaesthesia 18-20 seconds faster
- •If minimising recovery time is a priority, ketamine produces significantly faster standing times (25 min) compared to alfaxalone and thiopental (39-44 min), a clinically relevant 14-19 minute difference
- •All three agents appear clinically suitable alternatives for equine anaesthetic induction in this premedication protocol based on similar quality of induction/recovery and stable cardiopulmonary profiles
Key Findings
- •Alfaxalone and thiopental had significantly faster induction times (49s and 48s respectively) compared to ketamine (67s, P=0.01)
- •Recovery time to standing was significantly longer for alfaxalone (44 min) and thiopental (39 min) versus ketamine (25 min, P=0.01)
- •Anaesthetic induction and recovery quality scores were similar across all three drugs (P>0.05), with median scores ranging 3.5-5.0
- •All three agents maintained cardiovascular values within clinically acceptable ranges and preserved spontaneous breathing with PaCO2 approximately 50 mmHg