What are the variations in enzymes of drug metabolism?

Genetic polymorphism in enzymes of phase I and II In phase I (most common is CYP3A5 (CCB, cyclosporine), CYP2C8 (retinoic acid), CYP2C9 (NSAIDs, phenytoin, warfarin), CYP2C19 (omeprazol, phenytoin, propranolol) So most important active ones are CYP2C, CYP2D, CYP3A subfamilies