Plasma Protein: Non-Selective

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Plasma protein binding of drugs is non-selective, thus toxicants and drugs with similar physiochemical characteristics can compete with each other and endogenous substances for binding sites. Albumin is a major component responsible for the binding of most drugs in plasma. Acidic drugs bind primarily to albumin which is a drug-binding protein in plasma. The binding of drugs to plasma proteins and tissue binding sites is largely non-selective, which means many drugs with similar chemical properties can compete with each other for access to binding sites. However, it is suggested that the concern over the potential for adverse drug affects based on competitive displacement from plasma protein binding sites has been overstated. Indomethacin has been shown to decrease warfarin binding to human serum albumin, in vitro. This drug reaction has not been confirmed by in vivo studies. Because albumin and other plasma proteins have a limited number of binding sites, which are rather nonselective, two drugs with the same affinity for the same site will compete with one another. Multiple drugs that are highly bound to plasma proteins may compete with binding sites and a drug that binds with a higher affinity can displace another one. The result of this would be an increase in the intensity of pharmacologic action of the displaced drug or even an increase of the risk of adverse effects. Heredity, age, disease, sex, and other physiological conditions may also affect the extent of a drug binding to proteins. Displacement of a drug from its original plasma protein binding site can cause an elevation of free drug concentrations at the tissue receptor sites. The result is clinical toxicity even though the total plasma drug concentrations remain the same. The unbound portion of the drug increases as plasma protein-binding sites become saturated in overdose. This results in an

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