What drug has a 10 fold difference in Cmax, as a pharmacist I can’t think of anything even close to that.
That is to say, if we were to actually start assessing patients’ ability to metabolize warfarin we’d have to confront the fact that a huge number of bad clinical outcomes in the recent past stemmed from not doing this.
Healthcare systems are so aware of and open about warfarin's risks that they have warfarin clinics set up to repeatedly measure patients' prothrombin times so that they can adjust dosing empirically. Further, they also provide nutritional guidance to patients taking warfarin to help them reduce diet-influenced variance in warfarin metabolism.