Preprescription genotyping: not yet ready for prime time, but getting there.

There are few, if any, situations in medicine in which a clinician can predict with certainty an individual’s response to drug therapy. A host of factors can modulate this response: concomitant disease or drug therapy, sex, age, ethnicity, or dysfunction of excretory organs, to name but a few. Even when we correct for changes anticipated by such conditions, however, drug responses remain highly variable. It is an appealing concept, and one to which we subscribe, that some portion of this variability—and perhaps a great portion in many cases—is attributable to genetic factors. An increasingly sophisticated view of the genetic determinants of drug action in the context of complex diseases now raises the realistic expectation that this possibility can be addressed.