Field immobilization using alfaxalone and alfaxalone-medetomidine in free-ranging koalas (Phascolarctos cinereus): a...

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

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 (f_R), 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 f_R 10-15; p < 0.0001).

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.