The physiology of marsupials is well described by
Tyndale-Biscoe (2005). Marsupials have a lower metabolic
rate than eutherians. However, they require higher
dosages of injectable anesthetics than eutherians of
similar size. For example, three times as much xylazine/
ketamine is required to immobilize a possum than a cat
of similar size. The reasons are unknown.