Читать книгу Clinical Pharmacology and Therapeutics - Группа авторов - Страница 22

Once a drug has gained access to the bloodstream, it begins to distribute to the tissues. The extent of this distribution depends on a number of factors including plasma protein binding, lipid solubility and regional blood flow. The volume of distribution, V_D, is the apparent volume of fluid into which a drug distributes based on the amount of drug in the body and the measured concentration in the plasma or serum. If a drug was wholly confined to the plasma, V_D would equal the plasma volume – approximately 3 L in an adult. If, on the other hand, the drug was distributed throughout the body water, V_D would be approximately 42 L. In reality, drugs are rarely distributed into physiologically relevant volumes. If most of the drug is bound to tissues, the plasma concentration will be low and the apparent V_D will be high, while high plasma protein binding will tend to maintain high concentrations in the blood and a low V_D will result. For the majority of drugs, V_D depends on the balance between plasma binding and sequestration or binding by various body tissues, for example, muscle and fat. Volume of distribution can therefore vary considerably.