Key Factors Affecting the Absorption of Oral Drugs and Their Mechanisms

Abstract

Oral administration, as the most common route of drug delivery, is influenced by various complex factors during the drug absorption process. This article systematically elaborates on recent research progress regarding factors affecting oral drug absorption, including multiple dimensions such as physicochemical properties of drugs, physiological factors in organisms, and formulation characteristics. The absorption of orally administered drugs is a dynamic process involving multiple steps and factors that often interact in complex ways. Among these, solubility and permeability are considered core physicochemical parameters influencing both the speed and extent of oral drug absorption; most other physicochemical properties (such as lipophilicity, pKa value, molecular weight) ultimately regulate drug absorption indirectly through their effects on these two key parameters.

The Biopharmaceutics Classification System (BCS), an important predictive tool in drug development, classifies drugs into four categories (high solubility-high permeability, low solubility-high permeability, high solubility-low permeability, low solubility-low permeability), providing a scientific framework for drug development. Additionally, physiological factors such as gastrointestinal pH values, gastric emptying rates, small intestine transit times, bile secretion levels, and mechanisms of absorption significantly affect the bioavailability of orally administered drugs. By deeply understanding these influencing factors and their interaction mechanisms, drug developers can more accurately predict drug absorption characteristics and design optimized formulations to maximize bioavailability.

Introduction

Oral administration has become the most commonly used method due to its convenience and high patient compliance; however, the release from formulations and subsequent absorption processes are extremely complex. This process can be simplified into four key steps: first is the dissolution release from dosage forms; second is how well drugs dissolve in gastrointestinal environments depending on their physicochemical properties; third involves effective permeation across intestinal mucosa; finally, drugs may undergo metabolic processes before entering systemic circulation (i.e., first-pass effect). Each step could potentially become a bottleneck limiting drug absorption while there exists dynamic interdependence among all steps.

Factors affecting this above-mentioned absorbance process can be categorized into three main types: The first category includes intrinsic physicochemical properties of drugs like solubility, entero-permeability,pKa value,lipophilicitychemical stability,specific surface area,and particle size distribution.These inherent traits determine how medications behave within physiological environments.The second category encompasses physiological aspects related to organisms,such as pH gradients across different segments within gastrointestinal tracts,gastrointestinal motilities,time spent traversing through intestines,bile salt secretion levels,and various transport mechanisms involved with absorptions.All these elements create an environment conducive for optimal medication uptake.The third category pertains specifically towards formulation-related considerations which include choices made about dosage forms(solutions,capsules tablets,suspensions etc.)and applications concerning functional excipients.Formulation designs enable modulation over release profiles whilst improving overall conditions necessary for better uptake outcomes. This paper aims at comprehensively exploring diverse influences impacting oral medication uptake focusing primarily upon interactions between physiologically relevant variables alongside chemical attributes governing pharmaceutical performance.Additionally,it introduces insights surrounding BCS classifications’ significance throughout modern-day medicinal advancements.By systematically outlining said determinants,this work seeks offering theoretical foundations along practical guidance aiding both clinical practices & pharmaceutical innovations.