Estimating Drug Absorption Trends from Physiochemical Characteristics

Estimating Drug Absorption Trends from Physiochemical Characteristics 

It was postulated that the aqueous pores are available to all molecular species, both ionic and non-ionic, while the lipoidal pathway is accessible only to un-ionised species. In addition, Ho and co-workers introduced the concept of the aqueous boundary layer (ABL) [9, 10], The ABL is considered a stagnant water layer adjacent to the apical membrane surface that is created by incomplete mixing of luminal contents near the intestinal cell surface. The influence of drug structure on permeability in these domains will be different for example ABL permeability (Paq) is inversely related to solute size, whereas membrane permeability (Pm) is dependent on both size and charge. Using this model, the apparent permeability coefficient (Papp) through the biomembrane may therefore be expressed as a function of the resistance of the ABL and 

Dressman et al. [13] developed a dimensionless absorption potential (AP) model based on the concept that the fraction of dose absorbed, assuming negligible luminal instability and first-pass metabolism, is a function of drug lipophilicity (log P0/w), solubility (Sw), and dose (D), as defined in Eq. 2.7. 

More recently the H-bonding potential (an estimate of hydrophilicity) and surface charge characteristics of a molecule have been used as predictors of passive Pm and intestinal absorption [17, 18], Theoretical models based on the determination of polar surface area (PSA) have been utilised to reasonable 

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