Protein binding Factor affecting protein binding Methods to measure unbound protein

1. PROTEIN BINDING
Physical pharmaceutics

2. PROTEIN BINDING
● The phenomenon of complex formation of drug
with protein is called protein binding.
● A protein bound drug is neither metabolised
nor excreted hence it is pharmacologically
inactive.
● Protein + drug = Protein drug complex

3. Protein binding may be divided into
two groups-
● Reversible binding- The drug binds the
Protein with weak bonds such as-
hydrogen bonds or van der waals forces.
● These type of drugs can unbound and
shows its therapeutic action.

4. ● Irreversible binding- The drug binds
with protein by strong covalent
bonding and often a reason for the
carcinogenicity and toxicity.
● Order of binding of drug with
protein:
Albumin > glycoprotein >lipoprotein>
globulin

6. ● Binding of drugs to albumin
2.Digoxine
1. Warfarin & site
Azapropazone
4.Diazepam
sit
3. Tamoxifen
site

8. ● Significance of protein binding with drug:-
● Absorption- When there is more protein binding
by the drug then it will distrub the absorption
equilibrium.
● The rate of absorption is decreased when
protein is bind with drug.
● Distribution- The protein bound drug doesn’t
cross the BBB, placental barrier and glomerulus.
Thus it decrease the distribution of drug.

9. Metabolism- Protein binding decreases the
metabolism of drug and enhance the biological half
life. Only unbound fraction get metabolised.
Elimination- Only the unbound druf is capable of
being eliminated. Protein binding prevent the entry
of drug to the metabolizing organ (liver) and
glomerulus filtration.
Systemic solubility of drug – Lipoprotein act as
vehicle for hydrophobic drugs like steriods,heparin,
oil soluble vitamins.

10. Drug action- Protein binding inactivates the
drug because sufficient concentration of drug
cannot be build up in the receptor site for
action.
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replaced with radiolabeled l-131cab be used to
visualise melanomas of eyes and disorders of
thyroid gland.

11. Factors affecting protein binding
Drug related factors:
1. Physiochemical factors of drug- Binding affinity depend on physical and
chemical properties of drug.
Increase in lipophilicity Increase the drug binding with the protein.
2. Concentration of drug- Alteration in concentration of drug substance
as well as the protein molecules cause alteration in protein binding.
At low concentration, most drug may bound to protein.
At high concentration, more free drug may present owing to saturation
of binding site on protein.

12. 3. Affinity of drug for binding component-
● This depend on affinity of protein molecule to bind to drug.
● Eg. Digoxine hascmore affinity for protein of cardiac muscle
than those of skeletal muscles.
● Factors related to protein:
1.Physiochemical property- Lipoprotein bind with lipophilic drug.
2. Concentration of protein- Disease state affect the
concentration of protein in blood. It Increase the concentration of
protein and protein binding in the body.

13. 3.No. Of binding sites- Presence of more binding sites in protein
increase protein binding of drug.
Eg Albumin has more no. Of binding site.
● Factors related to age:
1.Age- Neonata have low albumin content thus less drug binding.
2. Disease state- Disease states increase the Albumin thus
increse protein binding.

14. Method of measuring the unbound drug concentration
● Equilibrium dialysis method
● In this method the Albumin is placed in visking cellulose bag and drug in
different concentration is placed in the outside vessel.
● As the dialysis continue, the drug molecules permeate through the
membrane and enter into the bag.
● As a result the dryg protein binding is observed. Albumin being
macromolecules can’t pass through the membrane to outside vessel.
● As time ellapsis more amount of drug permeate and available in the bag.
● If binding occurs the drug concentration in the body containing protein
should be greater than its concentration in the outside vessel.

15. 1. Equilibrium dialysis method

16. 2. Dynamic dialysis method:
● The apparatus consist of a 400ml jacketed (with a temperature control)
beaker into which 200ml of buffer solution is placed.
● Around 70ml of drug (blank) and drug protein solution is placed in a dialysis
bag and suspended in the buffer solution. The solution is is stir
continuously.
● During dialysis the free drug present in the bag permeate through the
membrane and reaches the buffer solution.
● Such a transport shift the equilibrium in favour of full drug molecules in the
bag.
● Every 5 or 10 mins. Sample of solution are withdrawn from the beaker and
an equivalent quantity of buffer solution is return to the beaker
● The amount of drug present in the solution is estimated by a suitable
method (UV rays)

17. 2. Dynamic dialysis method: