ABSTRACT
This chapter evaluates the various methods available that allow an estimation of the fraction of the dose absorbed following extravascular administration for the assessment of in vivo absorption kinetics. The correlation between the fraction of the dose absorbed in vivo and, for instance, the fraction of the dose released in vitro, allows establishment of some meaningful in vitro-in vivo correlation techniques to evaluate the pharmacokinetics of microsphere systems. The availability of sophisticated pharmaceutical microparticulate systems provide a wide choice of drug administration and absorption sites, rates of administration, and temporal profiles of drug absorption. Novel drug delivery systems invariably modify the release rate of the drug from the microparticulate system to allow a better pharmacokinetic profile of the drug. The regulatory assessment of these microparticulate systems requires demonstration of modified release, where possible by both in vitro and in vivo methods.
