Plasma Protein Binding of Drugs

Plasma Protein Binding of Drugs affects free drug levels, distribution, efficacy, and elimination in pharmacokinetics.

Mechanism of Plasma Protein Binding:

1. Reversible Binding: Drugs form non-covalent interactions (e.g., hydrophobic, hydrogen bonding, electrostatic) with plasma proteins, maintaining a dynamic equilibrium between bound and free drug.
2. Competition for Binding Sites: Multiple drugs can bind to the same site, leading to displacement and increased free drug concentration, potentially enhancing drug effects or toxicity.
3. Influence on Pharmacokinetics: High protein binding reduces volume of distribution (Vd) and slows drug clearance, prolonging half-life.

Types of Plasma Proteins Involved in Drug Binding:

1. Albumin: Binds primarily to acidic and neutral drugs; the most abundant plasma protein.
2. Alpha-1-Acid Glycoprotein (AAG): Binds mainly to basic drugs; concentration varies with disease or stress.
3. Lipoproteins: Transport lipophilic drugs, affecting their distribution and elimination.
4. Globulins: Some globulins, like sex hormone-binding globulin (SHBG) and corticosteroid-binding globulin (CBG), transport specific hormones and drugs with similar structures.
5. Fibrinogen: Involved in blood clotting, with a minor role in drug binding.

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