Figure 1 provides a diagram that summarizes the processes of distribution after the drug reaches the general circulation and demonstrates that drug distribution is critical in designing appropriate drug dosage regimens. This has led to the determination of "apparent" volumes of distribution (as discussed in chap. 3), which can be used to relate the amount of drug in the body (or in a hypothetical compartment of the body) to a measured plasma or blood concentration. The volume of distribution is a function of four major factors: (i) the size of the organs into which the drug distributes; (ii) the partition coefficient of the drug between the organ and the circulating blood; (iii) the blood flow to the distributing organs; and (iv) the extent of protein binding of the drug both in the plasma and in various tissues.
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