Allometric scaling calculator

When a species has no published dose, exotic practice sometimes scales one from a species that does, by metabolic rate rather than by body weight. This does that arithmetic — minimum energy cost, K × W^0.75 — and shows its working.

Extrapolation, not a published dose — use only when no species-specific dose exists; check the target species' own dose first.

Look the patient's species up in the dosage calculator or the drug catalog before using anything on this page.

Model species dose

mg/kg

Model dosing interval

hours

Single dose (no repeat interval)

Model body weight

Model group

The weight the published dose was established at. If the source gives none, this method has nothing to scale from.

Patient body weight

Patient group

Method and constants

MEC = K × W^0.75 · SMEC = K × W^−0.25 · patient dose = model dose × patient MEC ÷ model MEC · patient frequency = model frequency × patient SMEC ÷ model SMEC

Group	K
Passerine bird	129
Non-passerine bird	78
Placental mammal	70
Marsupial mammal	49
Reptile	10

Source: Mayer J. Allometric Scaling. In: Mader's Reptile and Amphibian Medicine and Surgery, 3rd ed. (2019), ch. 126 — Table 126.2, p. 1187; method and constants restated p. 1189.

Also printed in: Samour J (ed.). Avian Medicine, 3rd ed. (2016), Table 8-11 “Hainsworth’s Energy Groups”, p. 223 (129 / 78 / 70, credited there to Sedgwick 1993).

The method rests on metabolic rate alone and does not account for species differences in how a drug is absorbed, metabolised or eliminated (Mader 3e, p. 1189).
Many drugs are not suitable for scaling because hepatic drug metabolism differs between species (Samour, Avian Medicine 3e, p. 223).
Reptile metabolic rate depends on body temperature, so a scaled reptile dose assumes the species' optimal temperature; enrofloxacin clearance in green iguanas was not predictable by metabolic scaling (Mader 3e, p. 1186).
No constant is offered for amphibians, fish or invertebrates: neither held source prints one for drug scaling.

Reference only — verify before administering. This tool is for reference purposes only and does not constitute veterinary medical advice. Always consult a licensed veterinarian and verify dosages against current published literature before administering any medication. ExoticRx is not liable for clinical decisions. Full disclaimer