Pharmacokinetic variability

Most doctors do not fully appreciate just how much variability there exists in the population with respect to how their patients respond to a standard dose of the drug they use. Even without considering the variability in terms of the pharmacodynamics of the response, there is already a lot of variability. Here is a simple simulation of what a 'typical' plasma concentration profile might look like after a 8 hourly dosing regimen.

Looks fairly 'normal' doesn't it? But here (below), I have simulated a set of random profiles of a theoretical drug from a fictitious set of 20 patients with a very reasonable range of pharmacokinetic properties (body weight, clearance, volumes of distribution, bioavailability). These are values that one can reasonably expect from any patient. Just look at the wide range of plasma concentration profiles that can be found in a set of 20 'patients'. Whether these are eventually clinically important or not will of course, depend on the specific nature and the toxicity profile of the drug in question, but recognizing that such variability exists, is the first step to being able to personalize therapy.