that it is impossible to derive a single equation correlating body mass to metabolic
rate for all 6,000 species of reptiles (Funk 2000 ). Without knowledge of the extent
and route of elimination of a drug, extrapolation of dosage regimens from one
species to others is fraught with difficulty, if not impossible. Clearly, much more
research is needed on the drug metabolism and excretion mechanisms and path-
ways in nondomestic species. Such research generated data will increase the
ability of clinicians to determine more effective and safe dosage regimens for
their patients (Table 5 ). An additional consideration when using allometry is the
nonlinearity of pharmacokinetics of some drugs in some species (Manire et al.
2003 ; Rush et al. 2005 ). As stated by Fowler ( 1995 ), “no presently available
chemical restraint agent is equally effective and safe for use with all 45,000+
vertebrate species.” This statement can be extended from chemical restraint to
therapeutic use of drugs within veterinary medicine.
Table 4Examples of pharmaceuticals that are either good or
poor candidates for allometric scaling
Poor Good
Acetaminophen Ampicillin
Amikacin Apramycin
Amoxicillin Carbenicillin
Amphetamine Cephapirin
Antipyrine Chlortetracycline
Cefamandole Diazepam
Cefazolin Erythromycin
Cephalothin Gentamicin
Cloramphenicol Oxytetracycline
Digoxin Prednisolone
Fentanyl Tetracycline
Flunixin Thiamphenicol
Kanamycin
Ketamine
Ketoprofen
Levamisole
Lidocaine
Meperidine
Morphine
Oxyphenbutazone
Penicillin
Phenylbutazone
Phenytoin
Quinidine
Sulfadimethoxine
Sulfamethazine
Sulfathiazole
Theophylline
Ticarcillin
Tinidazole
Trimethoprim
Tylosin
Xylazine152 R.P. Hunter