The body temperature of eutherian mammals (placental mammals) is around 37 ◦ Celsius or 98.6 ◦ Farenheit. But as early as 1902, Martin1 reported that  marsupials (mammals with a pouch) have lower body temperatures (34.0 to 36.5 ◦ Celsius;  or 93.2 to 97.7 ◦ Farenheit).  In 1969 Dawson and Hulbert measured the oxygen consumption of different species of marsupials to determine the actual level of their energy metabolism.2  Dawson and Hulbert confirmed that the level of metabolism is approximately 30% lower than that found for eutherians.  Consequently this observation resulted in a long standing suggestion that has not yet been refuted, that medicine dosages for marsupials should be lower than those administered to eutherian species.3.

However there is no evidence that marsupials actually require a third less of the medicine dosage for it to be effective.  

Studies of antibacterial medicines such as amoxicillin, oxytetracycline and penicillin G in tammar wallabies (Macropus eugenii) 4, 5 and other studies in the koala and common brushtail possum have demonstrated marsupials have some very active metabolism pathways that break down some medicines rapidly in the body.6-8 Therefore there is no evidence that their lower ‘metabolic rate’ of marsupials should result in lower medicine dosages.

References

  1. Martin C. Temperature and metabolism in monotremes and marsupials. Phil Trans B 1902;195:1-37.
  2. Dawson T, Hulbert A. Standard energy metabolism of marsupials. Nature 1969;221:383.
  3. Sedgwick CJ. Allometric scaling and emergency care: the importance of body size. In: Fowler ME, editor. Zoo and Wild Animal Medicine: Current Therapy 3 W.B. Saunders Co., Philadelphia, Pennsylvania, 1993:34-37.
  4. McLelland DJ, Barker IK, Crawshaw G et al. Single-dose pharmacokinetics of oxytetracycline and penicillin G in tammar wallabies (Macropus eugenii). Journal of Veterinary Pharmacology and Therapeutics 2011;34:160-167.
  5. McLelland DJ, Rich BG, Holz PH. The pharmacokinetics of single dose intramuscular amoxicillin trihydrate in tammar wallabies (Macropus eugenii). Journal of Zoo and Wildlife Medicine 2009;40:113-116.
  6. El-Merhibi A, Ngo SNT, Jones BR et al. Molecular insights into xenobiotic disposition in Australian marsupials. Australasian Journal of Ecotoxicology 2007;13:53-64.
  7. Kimble B, Li KM, Valtchev P et al. In vitro metabolism of meloxicam in koalas (Phascolarctos cinereus), brushtail possums (Trichosurus vulpecula), ringtail possums (Pseudocheirus peregrinus), rats and dogs. Comparative Biochemistry and Physiology Part C, Pharmacology, Toxicology and Endocrinology 2014;161:7-17.
  8. Liapis P, Pass GJ, McKinnon RA, Stupans I. Characterisation of tolbutamide hydroxylase activity in the common brushtail possum (Trichosurus vulpecula) and koala (Pharscolarctos cinereus): inhibition by the Eucalyptus terpene 1,8-cineole. Comparative Biochemistry and Physiology Part C, Pharmacology, Toxicology and Endocrinology 2000;127:351-357.