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Drug Protein Binding
- 1. Drug-Protein Binding Course Title : Bio-pharmaceutics & Pharmacokinetics I Course Code : BPH 3019
- 2. Contents Competition for binding between drugs Binding of Class I and Class II drugs to albumin Clinical importance of drug displacement Effect of protein-binding on apparent volume of distribution Volume of distribution Effect of protein binding on elimination of drugs Drug protein binding: Relevance to treatment Conclusion
- 3. Competition for binding between drugs When two drugs are given, each with high affinity for albumin, they compete for the available binding sites. The drugs with high affinity for albumin can be divided into two classes, depending on whether the dose of drug is greater than, or less than, the binding capacity of albumin
- 4. Binding of Class I and Class II drugs to albumin Class I drugs: • If the dose of drug is less than the binding capacity of albumin, then the dose ratio is low. • The bound-drug fraction is high. Class II drugs: • Greatly exceed the number of albumin binding sites. • The dose/capacity ratio is high.
- 5. Clinical importance of drug displacement Drug classification assumes importance when a patient taking a Class I drug, such as warfarin, is given a Class II drug, such as a sulfonamide antibiotic. Warfarin is highly bound to albumin, and only a small fraction is free.
- 6. Effect of protein-binding on apparent volume of distribution The extent of drug protein binding in the plasma or tissue affects Vd. Drugs highly bound to plasma proteins have low concentration of free drug in the plasma water.
- 7. Effect of protein binding on elimination of drugs Protein binding decreases the renal excretion of drugs and enhances the biological half-life. The binding of drugs in extravascular organs decreases their concentration in blood. The binding of drugs to plasma proteins may either hasten or retard the elimination of drugs.
- 8. Drug protein binding: Relevance to treatment For a majority of drugs serum albumin is quantitatively the most important plasma protein. Globulin, lipoproteins and erythrocytes form other sites of binding. Equilibrium dialysis, gel-filtration and the ultrafiltration are the commonly used methods in drug protein binding.
- 9. Conclusion The phenomenon of complex formation of drug with protein called as Drug-Protein binding. The importance of such binding derives from the fact that the bound drug is both pharmacokinetically as well as pharmacodynamically inert. Of all types of binding, the drug-protein binding is most significant and most widely studied.