Protein Binding

                                      Drug Protein Binding 

Protein binding is the complex formation of endogenous/exogenous substances with proteins (free proteins or tissue complexes).

Protein binding is of two type one is irreversible and other is reversible.

Irreversible Protein Binding : is a chemical reaction. In which permanent bond formation occur i.e cove-lent bond (which is the case of Organo-phosphates poisoning permanent bonding with Acetylcholine  Esterase) and some carcinogenic elements which form permanent bonds with proteins attached to genetic material.

Reversible Protein Binding :is due to weak forces and complex can separate any time. Bonding involve may hydrogen and other weak forces.For pharmacokinetic point of view reversible binding is important.

On the other hand irreversible complex usually damage the tissue and may cause problem like carcinogenics.

In case of the reversible drugs binding drugs  having high binding capacity are bound to these proteins and there elimination is less leading to increase in Half-Life of the drugs. Filtration will also be limited and same is with distribution.

Types of Protein :

1)    Albumins: which are in the largest quantity. Plasma concentration is 3.5 to 5.5 %. Albumins are basic in nature so bind acidic drugs. They are transporter proteins carry drugs and endogenous substances from one location to the other in the blood.  Albumin build osmotic pressure in the vessels which in terms of proteins build pressure called oncotic pressure. Just like in case of burns when these protein goes out from vessels the blood volume reduces and result hypovolemic shock. Or in case of liver damage just like ascites. Example of Drugs binding to Salicylates, Phenylbutazone, Penicillines, Aldosterone, thyroxin.  

2)    Alpha acid Glycoprotein: Bind basic drugs because it is acidic. 0.4 to 1 % in the Blood. Its Concentration  is very low or no role in the osmotic phenomenon. Drugs binding to Alpha acid glycoproteins are imipramine, lidocaine and corticosteroids etc.

3)    Lipoproteins : they are involve in lipid transportation. They are important when albumins become saturated. Three classes VLDL, LDL and HDL.  They have negligible role in drug protein binding at normal physiological condition and have a prominent when Albumin saturation occur.

4)    Blood cells (RBCS): They too have binding Capacity. Make 45 % of the blood. Vary less amount of drug bind to these because of less affinity as compare to other proteins. And almost has no significance.

According to pharmacokinetic aspect albumin and alpha acid glycoprotein is important because relatively high amount of drug binds to these thus playing an active role in distribution phenomenon understanding.