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

5. Protein Binding

‒ Another factor that influences the distribution of drugs is binding to

Tissues Proteins

nucleic acids, albumins,
ligands,
globulins,
calcified tissues,
alpha-1-acid glycoprotein
adenosine triphosphatase

lipoproteins.

 It is the unbound or free portion of a drug that diffuses out of plasma.

► The protein-bound drug is:

– a large complex that cannot easily transverse cell or even capillary

membranes and therefore has a restricted distribution.

• Usually pharmacologically inactive. To exert an effect, the drug must

dissociate from protein.

• The free or unbound drug

– Crosses cell membranes and

– It is therapeutically active.

So, plasma proteins act as a reservoir or temporary storage place.

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