Warfarin is one of the most well known scientifically, but as a practitioner you may not know this because hospitals and insurers are scared to acknowledge the ongoing rate of preventable bad outcomes caused by not accounting for variances in metabolism.

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.

> hospitals and insurers are scared to acknowledge the ongoing rate of preventable bad outcomes caused by not accounting for variances in metabolism.

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.

Many tricyclic antidepressants metabolized by CYP2D6 would be here, if you put the nonmetabolizers up against the rapid metabolizer, https://en.wikipedia.org/wiki/Doxepin for example.

Cyclosporine and tacrolimus, if you look at the range in any of their pk trials you'll easily see 10 fold variability.

What about codeine with ultra-rapid metabolizers (e.g. the significant population in Saudi Arabia), it might not be a 10x difference but normal dosages can result in overdose or death in people that are ultra-rapid metabolizers or even in their babies if they are nursing mothers.

you're a bit behind on your CE time. There are lots with that high of variability.