Protein Binding Definition:
- Protein Binding: Drugs bind to plasma proteins (e.g., albumin, globulins) in the bloodstream, affecting their distribution and activity.
Importance in Drug Action:
- Free vs. Bound Drug: Only free drug is active; bound drug serves as a reservoir.
- Drug-Drug Interactions: Competition for binding sites can increase free drug concentration and toxicity.
- Duration of Action: High protein binding leads to longer half-life (e.g., warfarin).
- Tissue Distribution: Bound drugs stay in circulation, while unbound drugs move into tissues.
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Binding Dynamics:
- Reversible Interactions: Drugs typically bind non-covalently (through hydrogen bonds, van der Waals forces, and ionic interactions) to proteins. The bound drug is usually pharmacologically inactive, serving as a reservoir that releases the drug slowly.
- Equilibrium: The balance between bound and free drug is crucial; only the free form is able to cross cell membranes, bind to targets, or be metabolized.
Examples of Protein Binding:
- Warfarin (99
- Phenytoin: Displacement by another drug (e.g., valproate) increases toxicity.
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Factors Influencing:
- Drug’s physicochemical properties (charge, lipophilicity)
- Affinity for specific binding sites on proteins
- Concentration of both the drug and the protein
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