Physicochemical Properties Relevant to Diffusion

Mass (mg) First-Order Rate Zero-Order Rate 

The following physicochemical properties are important for chemical diffusion. We have discussed several of these properties in previous sections of this chapter as they relate to the passive diffusion mechanism and its impacts on rate of toxicant transport across membranes. 

Molecular size and shape Solubility at site of absorption Degree of ionization 

Relative lipid solubility of ionized and unionized forms 

Although molecular weight is important, it is less important than the drug s lipid solubility when it comes to assessing the rate of passive diffusion across membranes. 

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