Challenges in exploring the cytochrome P450 system as a source of variation in canine drug pharmacokinetics.

The cytochrome P450 (CYP) superfamily constitutes a collection of enzymes responsible for the metabolism of a wide array of endo- and xenobiotic compounds. Much of the knowledge on substrate specificity and genetic identification of the various CYP isoforms is derived from research in rodents and humans and only limited information has been captured in the dog. Currently, there exist many gaps in our knowledge of canine CYP diversity as a result of the paucity of studies focusing on canine CYPs, canine CYP polymorphisms, and the therapeutic consequences of these genetic variants. Challenges engendered by this lack of information is further amplified by inter- and intraspecies differences in the specificity and affinity of substrates and inhibitors, prohibiting a simple extrapolation of probe substances used in human CYP research. This creates a need to develop and validate canine-specific CYP probes. Failure to understand this potential metabolic and pharmacogenomic diversity can also influence the interpretation of data generated in dogs to support human drug development. It is with these objectives in mind that we provide an overview of what is currently known about canine CYPs with the hope that it will encourage further exploration into this important area of research