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    1. Pharmacology
        1.1. Basic principles of pharmacology
            1.1.1. Pharmacokinetics of injected drugs Protein-binding


[Ref: SH4:p12]


Most acidic drugs binds to albumin

Basic drugs bind to alpha1-acid glycoprotein

Importance of protein-binding

Only free (i.e. unbound) fraction is able to cross cell membrane



Changes in protein binding

Especially important for drugs which are normally highly protein-bound

Because small changes in binding
--> Large changes in free fraction

e.g. propanolol, phenytoin, diazepam


Determinants of protein binding


Plasma albumin binding is non-selective
--> Many drugs can compete with each other

For example,

Sulfonamides can displace unconjugated bilirubin from albumin
--> Higher risk of bilirubin encephalopathy in neonates


Protein binding and renal failure

In renal failure,
--> Protein-bound fraction of a drug decreases


Determinants of alpha1-acid glycoprotein level

Alpha1-acid glycoprotein may increase in response to:


Alpha1-acid glycoprotein are decreased in neonates
--> Decreased protein binding of diazepam, propanolol, sufentanil, lidocaine

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