Predicting Pharmacokinetics/Pharmacodynamics in the Individual Patient: Separating Reality From Hype

Individualization of patient drug dosing to maximize efficacy and minimize toxicity is the goal of clinical pharmacology. Here we review the history of drug dosing individualization from early predictions for renally eliminated drugs based on kidney function through the introduction of clearance concepts for metabolic processes, the differentiation of volume of distribution between pharmacokinetics and chemistry, the role of transporters, the unique pharmacokinetic aspects of oral dosing, and the relevance of protein binding to the emergence of pharmacogenomics. The Food and Drug Administration listing of pharmacogenomic markers in approved drug labeling is analyzed with respect to the promise of genomics in terms of picking the right drug for the patient based on genetic information vs selecting or adjusting the dosage regimen based on genetic information: the former resulting in a great advance, whereas the latter has shown less convincing evidence of clinical relevance. Finally, new information on individualized predictive methodologies based on marker drugs for enzymes and transporters is reviewed. We conclude that although individualization of drug dosing will work for most drugs primarily excreted unchanged in the urine, individualization of dosing regimens is not critical for wide-therapeutic-index drugs, whereas for narrow-therapeutic-index drugs predictions are most often more hype than reality, with therapeutic drug monitoring required. However, continuing advances in discovering and validating biomarkers will lead to predictions of pharmacokinetics/pharmacodynamics in the individualized patient that should result in shifting the hype to reality with time.