Membrane filtration method drugs

The answers are 31-b, 32-a, 33-d (Katzung, pp 4—7.) The absorption, distribution, and elimination of drugs require that they cross various cellular membranes The descriptions that are given in the question define the various transport mechanisms. The most common method by which ionic compounds of low molecular weight (100 to 200) enter cells is via membrane channels. The degree to which such filtration occurs varies from cell type to cell type because their pore sizes differ. 

Simple diffusion is another mechanism by which substances cross membranes without the active participation of components in the membranes. Generally, lipid-soluble substances employ this method to enter cells. Both simple diffusion and filtration are dominant factors in most drug absorption, distribution, and elimination. 

Cells do have other transport options. Very small molecules can filter through the various channel proteins in the membrane. Drugs tend to be too large to pass by this method. The filtration of water is specifically called osmosis. Endocytosis is another method by which molecules may enter a cell. Endocytosis comes in many forms, all of which involve the indentation of a section of cell membrane that pinches off to form a new internal vesicle in the cell (Scheme 3.2). Once the cell breaks down the vesicle, the contents are released... 

Pacifici and Viani, commenting on comparisons among results from different methods applied to protein binding, warn that methods for drug binding need to be standardized. Currently, results depend greatly on technique and interpretation of results thus, experimental details such as anticoagulant used, type of dialysis or filtration membrane, buffer characteristics, duration of experiment, and temperature should be taken into account. 

Our first result using the mass spectrometrie technique is the proof that pyrazofurin does exist in the free form in blood for a considerable period of time after dosing. Attention is called to the fact that in the method described proteins are removed by molecular filtration. With this technique only the free drug is detected since protein-bound molecules stay intact and cannot pass the membrane. 

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