Biopharmaceutics

Biopharmaceutics, in connection with pharmacokinetics, is the field that investigates and describes everything that happens with a medicinal product and the active substance between the moment of administration, the moment it exerts its action and the moment it is eliminated from the body. Biopharmaceutics connects the physico-chemical properties of an active substance and its dosage form, especially through the drug release characteristics, with its fate and action in the living organism. Actually biopharmaceutics describes how medicine formulation technologies can affect pharmacokinetics and pharmacodynamics. The route of administration, the way the active substance is released from the dosage form, and the way the body handles (absorbs, distributes, metabolises and excretes) the active substance, together determine its (duration of) action, its efficacy and the occurrence of adverse effects. This chapter explains general principles of biopharmaceutics and its relation to pharmacokinetics in the light of their implications on the design of medicines. It describes the general biopharmaceutical principles that are relevant to the major routes of administration: parenteral, oromucosal, oral, rectal, dermal, nasal, pulmonary and ocular. Topics discussed include solubility and dissolution, bioavailability, partition coefficient and pH partition theory, the biopharmaceutical classification system (BCS), excipient-, food-, drug- and herb-drug interactions, first-pass effects and drug metabolism, bioequivalence and new developments in the field of advanced drug delivery systems.