Drug absorption entails the movement of unchanged drugs to systemic circulation and their effectiveness is judged by the concentration at the site of action. Drug distribution involves the transfer of drugs between compartments, including blood and tissues, with specific mechanisms like endocytosis playing a key role in nutrient and vitamin uptake. The plasma membrane's fluid mosaic model describes the arrangement of proteins and phospholipids that facilitate these processes.

1. Drug Absorption and Distribution

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Drug Absorption
The process of movement of unchanged drug from
the site of administration to systemic circulation
The effectiveness of a drug can only be assessed by its
concentration at the site of action.

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Drug Distribution
Reversible transfer of drugs between one compartment
and another ( between blood & extravascular fluids &
tissues)

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Drug Distribution
 Permeation of free or unbound drug into interstitial /
extracellular fluid
 Permeation of drug present in extracellular fluid into
intracellular fluid { rate limiting step}

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Plasma Membrane
Fluid mosaic model:
Working model of the membrane
Protein molecules bobbing in phospholipid sea
Proteins determine membrane’s specific functions
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MECHANISMS OF DRUG ABSORPTION

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• It is a form of endocytosis in
which small particles are
brought to the cell, forming an
invagination.
• These small particles are
suspended in small vesicles.
• It requires energy in the form
of ATP.
• This process is important in
the absorption of oil soluble
vitamins & in the uptake of
nutrients
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