ABSTRACT
Pharmacokinetic assessment of new drug entities forms a pivotal part of any pharmaceutical development programme. Although primarily providing data to support toxicological and efficacy studies, carefully designed and executed pharmacokinetic studies in early drug development can greatly enhance decision-making processes involved in formulation development, as well as providing indications of potential problems that may arise later in the clinical assessment of the new drug entity. This chapter focuses on these two areas of investigation: one established practice and one causing increasing concern to the regulatory agencies. The extent of absorption is much more readily quantified than the absorption rate and is usually equated with the fraction of the administered dose that reaches the systemic circulation as unchanged drug. Assessment of the extent of absorption almost invariably relies upon an estimation of the area under the plasma drug concentration–time curve.
