Field immobilization using alfaxalone and alfaxalone–medetomidine in free-ranging koalas (Phascolarctos cinereus): a randomized comparative study

Published:February 27, 2020DOI:



      To characterize and compare two intramuscular drug protocols using alfaxalone and alfaxalone–medetomidine combination for the field immobilization of free-ranging koalas.

      Study design

      Blinded, randomized, comparative field study.


      A total of 66 free-ranging koalas from the Mount Lofty Ranges, South Australia.


      Koalas were randomly allocated into two groups. Group A animals were given alfaxalone alone at 3.5 mg kg–1. Group AM animals were given alfaxalone 2 mg kg–1 and medetomidine 40 μg kg–1, reversed with atipamezole at 0.16 mg kg–1. Blinded operators recorded heart rate (HR), respiratory rate (fR), cloacal temperature, depth of sedation and times to: first effect, sedation suitable for clinical interventions, first arousal and full recovery. Data were analysed using independent t test, Mann–Whitney U test, chi-square analysis and log-rank test at 5% level of significance.


      Suitable immobilization for clinical examination and sample collection was achieved in all animals. In groups A and AM, median time to working depth was 6.5 minutes (range: 3.4–15) and 8.1 minutes (range: 4.3–24) and time to complete recovery was 66 minutes (range: 12–138) and 34 minutes (range: 4–84), respectively, following reversal. Time to first effect was significantly shorter in group A (p = 0.013), whereas time to full arousal was significantly shorter in group AM (p = 0.007) probably due to the administration of atipamezole. Maximum HR was 117 ± 28 beats minute–1 in group A, which was a significant increase from baseline values (p < 0.0001), whereas group AM showed a significant tachypnoea of 67 ± 25 (normal fR 10–15; p < 0.0001).

      Conclusions and clinical relevance

      Both the protocols produced immobilization, enabling clinical examination and sample collection; however, protocol AM was more suitable for field work due to shorter recovery times.


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