Preabsorptioon

Preabsorptioon is a term used in pharmacology and nutrition to describe the set of events and barriers that occur before a substance enters the systemic circulation. It encompasses physicochemical properties, formulation factors, and physiological conditions that determine how much of a compound can be absorbed after oral administration.

Key preabsorptive processes include disintegration of the dosage form and dissolution of the drug in the gastrointestinal fluids, which are governed by solubility, particle size, and polymorphism. The rate and extent of dissolution are influenced by pH-dependent ionization, as the stomach is highly acidic while the small intestine has a more neutral to slightly basic environment. Food intake, gastric emptying, and intestinal transit time further modulate exposure and absorption.

Interactions in the gut lumen and at the intestinal mucosa also matter. Some drugs undergo enzymatic metabolism or are transported back into the lumen by intestinal enzymes or transporters, reducing the amount that reaches the bloodstream. Lipophilic drugs may require bile salts and micelle formation for effective solubilization, while poorly soluble compounds may be dissolution-limited in the preabsorptive phase.

Implications of preabsorptioon include its influence on oral bioavailability and interindividual variability. It guides formulation strategies such as salt forms, solid dispersions, nanoparticles, and lipid-based delivery systems designed to enhance dissolution and absorption. In research and development, preabsorptive factors are evaluated using in vitro solubility tests, permeability models (e.g., Caco-2), and pharmacokinetic modeling to predict systemic exposure and optimize dosage forms.