Practical Matters: Carefully consider drug dosages in puppies and kittens

Little research has been done demonstrating the pharmacokinetics of drugs commonly administered to puppies and kittens or defining the safe and effective doses of these drugs. When considering giving a particular drug, you must think about pediatric physiology and the absorption, metabolism, and excretion of the chosen drug.

Margaret V. Root Kustritz, DVM, PhD, DACT

Hepatic gluconeogenesis, glycogenolysis, protein synthesis, and bile acid metabolism are decreased in pediatric animals, with adult values achieved after 8 weeks of age.1 These decreases may alter the rate at which drugs are metabolized and will alter the distribution of drugs that are protein-bound in the circulation.

The glomerular filtration rate is reduced in puppies and kittens, varying from 20% of adult values at birth to 100% of adult values by several weeks of age.1 Decreased glomerular filtration is associated with longer drug circulation because of decreased excretion rate.

For example, consider a 2-week-old puppy. In dogs, 13% of amoxicillin is bound to protein in circulation. It is metabolized in the kidney and liver and excreted in the urine. Because most of the active drug is not protein-bound, the puppy's decreased protein synthesis may be disregarded. However, decreased hepatic and renal function will increase the amount of time active amoxicillin is in the circulation. Thus, you may consider administering the adult dose but at less frequent intervals.

Margaret V. Root Kustritz, DVM, PhD, DACT

Department of Veterinary Clinical Sciences

College of Veterinary Medicine

University of Minnesota

St. Paul, MN 55108

REFERENCE

1. Root Kustritz MV. Neonatology. In: The practical veterinarian: small animal theriogenology. St. Louis, Mo: Butterworth-Heinemann, 2003;283-329.