Factors Influencing Absorption and Distribution
Drug Disposition
Most drugs act via receptors and the effect of the drug is directly related to its concentration in the fluid surrounding the receptor. Since most drugs are conveyed to the tissues via the blood, the tissue concentration will be related to the plasma concentration. This relationship is extremely indirect and involves the passage of drugs across membranes.
In order to reach its site of action, a drug often has to cross several membranes. The ability of a drug to cross membranes will affect all aspects of its disposition in the body.
The mechanisms of transfer include: