Table 1.

PGx variants determining drug responses.

Class	Description	Example genes or gene products	Primary effect	Example gene biomarker and drug pair- human	Example gene biomarker and drug pair- veterinary spp.	Potential clinical approach
Pharmacokinetic	Genes relating to ADME	Cytochrome P 450 (CYP) enzymes, drug transporters	Alter concentration of the active drug at the intended or at an unintended site of drug action	CYP2C9 and warfarin (45) CYP2D6 and codeine (46) CYP2B6 and propofol (47)	Equine CYP2D50 and tramadol (48) Canine ABCB-1 and ivermectin (35)	Change drug dose; choose alternate drug with different ADME
Pharmacodynamic	Genes that encode the intended drug target	Cell surface receptors and intracellular enzymes	Alter the levels of the drug target or alter the ability of a drug to bind to drug target	VKORC1 and warfarin (45)	Canine OXTR and oxytocin (49) Canine PDE5A and sildendafil (50)	Change drug dose; choose alternate drug with different target
Pathway	Genes that encode proteins in the downstream pathway of drug	Signaling molecules, cellular pathways, transcription factors	Alter the activity of the pathway targeted by drug therapy	LDLR and statins (51)	–	Change drug dose; choose alternate drug with different drug pathway
Off-target	Genes that encode proteins that are not in the downstream pathway of drug	Immune recognition proteins	Generate an immune or other response to drug or metabolite	HLA-B and abacavir (52)	MHC genes and idiosyncratic responses? Porcine (30), Canine (53) & Equine (54) RYR1 and halothane/sevoflurane	Change drug dose; choose alternate drug with different chemical structure

Adapted from Voora (2).