A Mechanistic Approach to Understanding the Factors Affecting Drug Absorption: A Review of Fundamentals
AbstractThis article provides an overview of the patient-specific and drug-specific variables that can affect drug absorption followingoral product administration. The oral absorption of any chemical entity reflects a complex spectrum of events. Factors influencingproduct bioavailability include drugsol ubility, permeability, and the rate of in vivo dissolution. In this regard, the Biopharmaceutics Classification System has proven to be an important tool for predictingcompounds likely to be associated with bioavailability problems. It also helps in identifyingthose factors that may alter the rate and extent of drugabsorption. Product bioavailability can also be markedly influenced by patient attributes such as the integrity of the gastrointestinal tract, physiological status, site of drugabsorption, membrane transporters, presystemic drug metabolism (intrinsic variables), and extrinsic variables such as the effect of food or concomitant medication. Through an awareness of a drug's physicochemical properties and the physiological processes affectingdrugabsorption, the skilled pharmaceutical scientist can develop formulations that will maximize product availability. By appreciatingthe potential impact of patient physiological status, phenotype, age, gender, and lifestyle, dosingregimens can be tailored to better meet the needs of the individual patient.