At this point in the course, we have considered many aspects of pharmacokinetics. We have studied “rapid metabolizers” of codeine in unit 2, and you are currently studying renal drugs and the most important determinant of drug dosing in the elderly–creatinine clearance. Recently, new renal markers have been identified that can help monitor kidney function (and ostensibly, drug clearance) even before serum creatinine levels increase. In the cardiac drugs, we have examined the different aspects of warfarin metabolism in patients who have varying responses to that drug. And by now, hopefully, you are also getting an appreciation for a certain handful of drugs that you must always be mindful and careful of–the drugs that are potent inhibitors or inducers of certain P450 enzymes and P-glycoprotein. When you consider that the average 65-year-old American takes 13-16 medications at any given time, the worry of polypharmacy, drug interactions, and adverse reactions is very real!