Factors influencing drug absorption through GIT. Biopharmaceutics.

Drug absorption is a fundamental process in biopharmaceutics that determines the rate and extent to which a drug enters the systemic circulation after administration. For orally administered drugs, absorption mainly occurs through the gastrointestinal tract (GIT), particularly in the small intestine, because of its large surface area, extensive blood supply, and favorable physiological conditions. The absorption process is influenced by several drug-related, physiological, and formulation-related factors, which ultimately affect the bioavailability and therapeutic response of a medication.

Physicochemical properties of the drug play an important role in absorption. Factors such as aqueous solubility, lipid solubility, particle size, molecular size, degree of ionisation, and pKa influence the ability of a drug to dissolve in gastrointestinal fluids and cross biological membranes. The dosage form and formulation can also affect drug absorption through differences in disintegration, dissolution, drug release, and stability within the GIT. Different pharmaceutical formulations may therefore produce significant differences in the rate and extent of absorption.

Physiological factors are equally important. Gastrointestinal pH, gastric emptying time, intestinal motility, gastrointestinal blood flow, and the presence or absence of food can alter drug dissolution and movement through the GIT. The composition of gastrointestinal fluids and the activity of digestive enzymes may also influence drug stability and absorption. In addition, interactions with other drugs, nutrients, and gastrointestinal contents can modify the absorption of certain medicines.

Biological factors, including membrane permeability, intestinal transporters, and presystemic metabolism by intestinal enzymes and the liver, further determine the amount of drug reaching systemic circulation. Understanding these factors is essential for predicting drug absorption, optimising dosage forms, improving bioavailability, and ensuring consistent therapeutic effects. Therefore, the study of factors influencing drug absorption through the GIT is an important aspect of biopharmaceutics and pharmaceutical formulation.

Dr Alok Bains

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https://drive.google.com/file/d/1wk0UKMfoVhINWvOCDLi4mWSBzawufYA7/view?usp=drive_link