Page 134 - Interactive Theoritical Notes of Bioharmaceutics and pharamcokinetics.docx compressed

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

1. Body Tissue Characteristics

❑ Blood flow to different organs of the body is not equal.

➢ Certain organs, such as the heart, lungs, and kidneys, are highly perfused with

blood.

➢ Fat tissue and bone (not the marrow) are much less perfused.

➢ Skeletal muscle is intermediate in blood perfusion.

❑ The importance of these differences in perfusion is that for most drugs: the rate

of delivery from the circulation to a particular tissue depends greatly on the blood

flow to that tissue.

 This is called perfusion-limited distribution.
❑ Perfusion rate limitations occur when the membranes present no barrier to

distribution.
❑ The rate-limiting step is how quickly the drug gets to the tissue.

❑ If the blood flow rate increases, the distribution of the drug to the tissue increases.

Therefore, drugs apparently distribute more rapidly to areas with higher blood

flow.

❑ Highly perfused organs rapidly attain drug concentrations approaching those in

the plasma.

❑ Less well-perfused tissues take more time to attain such concentrations.

❑ If blood flow was the only factor affecting distribution, it would be

reasonable to expect that high concentrations of administered medications would

always appear in the brain and liver.

❑ In reality, few drugs exhibit good penetration of the central nervous system.

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