Drugs are Absorbed in Finite Time: A New Era in Biopharmaceutics and Pharmacokinetics

From the early days of Pharmacokinetics (1) drug absorption was modeled as a first-order process implying an infinite time for drug absorption. According to the current scientific knowledge and common wisdom, drugs are absorbed passively in finite time. The concept of “finite time” of absorption has been used in various Physiologically Based Pharmacokinetic (PBPK) models. However, the formal development of Physiologically Based Finite Time Pharmacokinetic (PBFTPK) models was published recently (2-5). The PBFTPK models were built on two principles: i) drugs are absorbed passively for a finite period of time, τ and ii) time absorption constrains linked with the gastrointestinal transit times of drug in the stomach, the small intestines and the colon were applied (2-5). Zeroor first-order input is used for the (PBFTPK)0 and (PBFTPK)1 models, respectively.