Page 132 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

Drug distribution

It is the process of reversible transfer of drug to and from the site of measurement

(usually blood or plasma). Any drug that leaves the site of measurement and does not

return has undergone elimination.

▪ The rate and extent of drug distribution is determined by:

1. How well the tissues and/or organs are perfused with blood

2. The binding of drug to plasma proteins and tissue components

3. The permeability of tissue membranes to the drug molecule.

▪ After a drug is absorbed in to plasma, the drug molecules are distributed throughout

the body by the systemic circulation. The drug molecules are carried by the blood to

the target site (receptor) for drug action and to other (nonreceptor) tissues as well,

where side effects or adverse reactions may occur.

▪ Drug molecules are distributed to eliminating organs, such as the liver and kidney,

and to non-eliminating tissues, such as the brain, skin, and muscle.

• In pregnancy, drugs cross the placenta and may affect the developing fetus.

• Drugs can also be secreted in milk via the mammillary glands.

• A substantial portion of the drug may be bound to proteins in the plasma and/or

tissues.

• Lipophilic drugs deposit in fat, from which the drug may be slowly released.

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