• Agrionemys horsfieldii ;
  • alfaxalone;
  • anaesthesia;
  • chelonian;
  • medetomidine;
  • tortoise



To characterise four different intramuscular (IM) anaesthetic protocols, two with alfaxalone and two with alfaxalone in combination with medetomidine in terrestrial tortoises.

Study design

Blinded, randomized, cross-over experimental study.


Nine healthy adult male Horsfield's tortoises (Agrionemys horsfieldii).


Each tortoise was randomly assigned to one of four different protocols: 1) 10 mg kg−1 alfaxalone; 2) 10 mg kg−1 alfaxalone + 0.10 mg kg−1 medetomidine; 3) 20 mg kg−1 alfaxalone; and 4) 20 mg kg−1 alfaxalone + 0.05 mg kg−1 medetomidine. During the experiment, the following variables were recorded: heart rate; respiratory rate; peripheral nociceptive responses; muscle strength; ability to intubate; palpebral, corneal and tap reflexes; and cloacal temperature.


Protocols 1 and 2 resulted in moderate sedation with no analgesia, and moderate to deep sedation with minimal analgesia, respectively. Protocols 3 and 4 resulted in deep sedation or anaesthesia with variable analgesic effect; these two protocols had the longest total anaesthetic time and allowed intubation in 6/9 and 8/9 tortoises respectively. The total anaesthesia/sedation time produced by alfaxalone was significantly increased (< 0.05) by the addition of medetomidine. There were no significant differences regarding time to plateau phase and duration of plateau phase. Baseline heart rate of 53 ± 6 beats minute−1 decreased significantly (< 0.05) with all protocols, and was lower (< 0.05) in protocols 3 and 4. Heart rate increased after atipamezole administration, but the increase was transient. In two tortoises, extreme bradycardia with no cardiac activity for 10 minutes was observed with protocols 3 and 4.

Conclusion and clinical relevance

Alfaxalone 10 and 20 mg kg−1 IM can be used for sedation for non-painful procedures. Alfaxalone in combination with medetomidine can be used for deeper sedation or anaesthesia, but the observed respiratory and cardiovascular depression may limit its use.