Drug absorption factors affecting

Fig. 11 The influence of food on factors that affect the sequential steps leading to GIT drug absorption, systemic availability, and elimination. (Copyright 2000 Saguaro Technical Press, Inc., used with permission.)...

Drugs in Class II have low aqueous solubility (but high membrane permeability), and any factor affecting dissolution rate would be expected to have an impact on the absorption of such compounds. Factors that are noted in Fig. 11, such as fluid pH, volume and viscosity, and bile secretion (especially in response to fatty foods), might be expected to play a role in dissolution rate and thereby affect absorption. Compounds that fall into this class include carbamazepine, cyclosporin, digoxin, griseofulvin, and spironolactone. Food would be expected to exert a potentially significant affect on... 

Fig. 8 Factors affecting the rate of absorption of drug from the gastrointestinal tract. (From Ref. 15.). 

A biologically important factor affecting drug absorption is drug metabolism or reaction coincident with diffusion across a membrane. The reaction often produces inactive or less potent products than the parent drug. It is conceivable that the reaction will also reduce the drug flux into the systemic circulation. We are interested in the effect of reaction on membrane diffusion. 

Solubility, dissolution rate, and intestinal permeability, are the major bio-pharmaceutic factors that affect the rate and extent of absorption of an oral drug product. Particularly for water insoluble drugs that have generally high membrane permeability (BCS Class II), dissolution, and dose are the most critical factors affecting the rate and the extent of oral absorption. 

The interaction between drugs in the lumen and intestinal components is generally a poorly studied area, and it is difficult based on in vivo data to discriminate such effects from other factors affecting absorption. In addition, evidence for the in vivo relevance of available in vitro methods is sparse. 

FACTORS SUCH AS CHARGE THAT AFFECT DRUG ABSORPTION, DISTRIBUTION, AND EXCRETION... 

Table 5.1 Some factors that affect nasal drug absorption in vivo [2],...

Table 6.1 Factors That May Affect Pulmonary Drug Absorption and Disposition (Modified from Tronde [139]). ...

In relation to systemic absorption of drugs, absorption in the lung can be described as the passage of a series of barriers by the drug in order to enter the systemic circulation. It is important to realize that physiological conditions in the lung differ widely from site to site. Major physiological factors that affect pulmonary absorption are [10] ... 

Patients can exhibit alterations in the rate and extent of drug absorption because of various factors. All of the following factors might affect the rate and/or extent of drug absorption EXCEPT ... 

The biological factors which affect the drug absorption are ... 

The physicochemical factors affecting the absorption are lipid solubility, dissolution rate, salt from complexation, viscosity and drug stability in the GIT. 

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