Helle Hydeskov, Cathrine Dyhr Sauer, Mads Bertelsen

Objective To characterise the anaesthetic effects of alfaxalone administered at 10, 20, and 30 mg kg^-1 intramuscularly (IM).

Study design Prospective, randomized cross-over study.

Animals 10 juvenile green iguanas (Iguana iguana). Mean body weight (±SD) was 480 ± 134 g.

Methods Alfaxalone was administered intramuscularly in the triceps region of both front legs. Duration of anaesthetic induction, plateau phase and recovery were recorded. Skeletal muscle tone of jaw, neck, forelimbs, hindlimbs, and tail, the presence of palpebral, corneal, and righting reflexes, as well as the response to painful stimuli were assessed, and heart rate and respiratory rate were recorded. Comparisons across dosages and over time were made using ANOVA.

Results Mean induction time was 7.7±2.2, 5.4±1.7 and 3.9±1.2 minutes for 10, 20 and 30 mg kg^-1, respectively. Duration of the plateau phase was 11.3±3.8, 22.1±6.5 and 39.1±11.5 minutes respectively. Recovery time was 10±2.4, 17.5±8.6 and 25±7.1 minutes respectively, and total anaesthetic duration was 29±5.7, 45±8.2 and 68±9.8 minutes respectively. Endotracheal intubation was possible in 40% of the subjects with 10mg kg^-1 and 100% with 20 and 30mg kg^-1. Loss of peripheral pain sensation was seen in 0/10, 8/10 and 9/10 trials at 10, 20, and 30mg kg^-1 respectively.

There was an initial dose-dependent depression of respiration followed by a significant increase in frequency over time. In contrast, heart rates decreased by 20% over the duration of the anaesthetic events.

Conclusions and clinical relevance –Intramuscular administration of alfaxalone is a simple, rapid and reliable means of achieving relatively brief sedation/anaesthesia in healthy green iguanas. 10mg kg^-1 provides light sedation, appropriate for examination, venipuncture etc., 20mg kg^-1 provides a level suitable for minor procedures or for endotracheal intubation and supplementation with inhalational anaesthesia. At 30mg kg^-1 alfaxalone provides an anaesthetic plane suitable for surgical procedures of limited duration (up to 40 minutes).