Distribution

Distribution

Drug distribution is the process by which the drug is delivered from the systemic circulation to body tissues and fluids. Distribution of an absorbed drug within the body depends on several factors:

• blood flow
• solubility
• protein binding.

Quick to the heart

After a drug has reached the bloodstream, its distribution in the body depends on blood flow. The drug is quickly distributed to organs with a large supply of blood. These organs include the:

• heart
• liver
• kidneys.

Distribution to other internal organs, skin, fat, and muscle is slower.

Lucky lipids

The ability of a drug to cross a cell membrane depends on whether the drug is water or lipid (fat) soluble. Lipid-soluble drugs easily cross through cell membranes; water-soluble drugs can’t.

Lipid-soluble drugs can also cross the blood-brain barrier and enter the brain.

Free to work

As a drug travels through the body, it comes in contact with proteins such as the plasma protein albumin. The drug can remain free or bind to the protein. The portion of a drug that’s bound to a protein is inactive and can’t exert a therapeutic effect. Only the free, or unbound, portion remains active.

A drug is said to be highly protein-bound if more than 80% of the drug is bound to protein.