Physicochemical, Pharmaceutical, and Biological Considerations in GIT Absorption of Drugs

Foremost considerations in the formulation of a drug product include the therapeutic goal, the site of application, and systemic drug absorption from that site. In particular, if the drug formulation is meant for systemic action via the oral route, the drug should preferably be entirely and steadily absorbed from the gastrointestinal (GI) site. Moreover, the systemic absorption of a drug is dependent on the physicochemical characteristics of the drug, the nature of the drug product, and the anatomy and physiology of the drug absorption site (GI site). Furthermore, to develop a drug product that elicits the desired therapeutic goal, the formulation scientist must have a complete knowledge of the biopharmaceutical characteristics of the drug and drug product and the physiologic and pathologic factors affecting drug absorption from the application site. This chapter focuses on the anatomical and physiological considerations for the systemic absorption of a drug along with a special mention of the physicochemical, biopharmaceutical, and biological aspects of the drug absorption. We also attempted to provide a reader a brief outlook on the chemical nature of the drug substance.