Canine Cytochrome P-450 Pharmacogenetics

The cytochrome P450 (CYP) drug metabolizing enzymes are essential for the efficient elimination of many clinically used drugs. These enzymes typically display high interindividual variability in expression and function resulting from enzyme induction, inhibition, and genetic polymorphism thereby predisposing patients to adverse drug reactions or therapeutic failure. There are also substantial species differences in CYP substrate specificity and expression that complicate direct extrapolation of information from humans to veterinary species. This article reviews the available published data regarding the presence and impact of genetic polymorphisms on CYP-dependent drug metabolism in dogs in the context of known human-dog CYP differences. Canine CYP1A2, which metabolizes phenacetin, caffeine, and theophylline, is the most widely studied polymorphic canine CYP. A single nucleotide polymorphism resulting in a CYP1A2 premature stop codon (c.1117C>T; R383X) with a complete lack of enzyme is highly prevalent in certain dog breeds including Beagle and Irish wolfhound. This polymorphism was shown to substantially affect the pharmacokinetics of several experimental compounds in Beagles during preclinical drug development. However, the impact on the pharmacokinetics of phenacetin (a substrate specific for human CYP1A2) was quite modest probably because other canine CYPs are capable of metabolizing phenacetin. Other canine CYPs with known genetic polymorphisms include CYP2C41 (gene deletion), as well as CYP2D15, CYP2E1, and CYP3A12 (coding SNPs). However the impact of these variants on drug metabolism in vitro or on drug pharmacokinetics is unknown. Future systematic investigations are needed to comprehensively identify CYP genetic polymorphisms that are predictive of drug effects in canine patients