Chapter 13 Absorption and bioequivalence

Abstract

Publisher Summary This chapter focuses on the use of stable isotopes to investigate drug absorption and elucidate bioavailability and bioequivalence. Bioavailability investigations are generally concerned with defining either absolute or relative bioavailability. Absolute bioavailability studies use an intravenous dose as the reference against which the test dosage form is compared. Definitive bioavailability/bioequivalency studies require a fairly large number of subjects to achieve the necessary statistical power to confirm equivalence. The validity of cross-over study results is based on the assumption that a drug's clearance remains constant as a function of time. The absolute bioavailability of a given drug formulation can be determined in a study by the simultaneous administration of an intravenous stable isotope labeled drug solution and the unlabeled comparative formulation. The relative bioavailability of the widely prescribed antiarrhythmic drug, verapamil, has been examined using stable isotope techniques. Transdermal delivery systems containing nicotine are readily available as an adjunct to smoking cessation therapy. The relationship between drug release from the delivery system and blood levels is well characterized and the need for maintaining continual blood levels of nicotine is considered necessary for the desired therapeutic effects.