Concepts of veterinary practice in wild mammals.

At the beginning of this article, we described the challenge faced by wildlife veterinarians in extrapolating treatment regimens and finding data bases of physiologic variables with which to assess health or depth of anesthesia in wild mammals. For example, we might wish to administer injectable ivermectin to a 75-kg deer and a 75-g squirrel for treatment of intestinal nematodes. An effective dose of ivermectin for the 75-kg deer is 0.2 mg/kg SC, and for the 75 g (0.075 kg) squirrel is 1.3 mg/kg SC. Given the squirrel dose (1.3 mg/kg), the deer could be made very ill or even killed by the treatment; whereas given the deer dose (0.2 mg/kg), the squirrel would not receive enough ivermectin to achieve a therapeutic level. This is the reason for allometric scaling of drug doses. Scaling doses allometrically is an arithmetic procedure that is more precise than trying to extrapolate doses between animals of diverse body sizes (such as the ermine and the wolverine) and between species that have different core body temperature set points (such as marsupial and placental mammals). For many years, in human and veterinary medicine, practitioners have allometrically scaled doses of potentially toxic chemotherapeutic agents using either (1) mg or micrograms drug/M2 body surface area or (2) mg or micrograms of drug/SMEC. Allometric calculations give results that are much more predictable and take into consideration substantial differences in body size and core body temperature.