PROTEIN BINDING, FACTOR AFFECTING PROTEIN BINDING, KINETICS OF PROTEIN BINDING, AND SIGNIFICANCE OF PROTEIN BINDING

1. MANISH KUMAR SHARMA
MAIP, JAIPUR

2.  INTRODUCTION
 CONSIDERATIONS OF THE STUDY for DRUG PROTEIN
BINDING
 BINDING OF DRUGS TO BLOOD COMPONETNTS
 EFFECT OF PROTEIN BINDING ON APPARENT VOLUME
OF DISTRIBUTION
 FACTORS AFFECTING OF PROTEIN BINDING
 KINETICS OF PROTEIN-DRUG BINDING
 SIGNIFICANCE OF PROTEIN BINDING

3. Bound Drug is Pharmaodynamicaly inert.
Binding: Half life of drug.
Bonding : Hydrogen bond, Hydrophilic bond,
ionic bond, Vander Walls bond.
Irreversible bonding : Covalent bonding :
responsible for the Carcinogenicity or Tissue
toxicity.
3

4. To Blood
components
1. Plasma
Proteins
2. Blood
cells
To Extra
vascular
Tissues
1.
Proteins
2. Fats
3. Bones ,
etc.

6. •Albumin m.wt 65,000 – 69,000
•It is synthesized in the liver .
•It is major component of plasma proteins.
•Responsible for reversible drug binding .
•Albumin is distributed in the plasma and in the
extracellular fluids of skin , muscle ,and various
tissues.
•Intestinal fluid albumin concentration is about 60% of
that in the plasma .

7. Elimination half life of albumin: 17-18
days .
Albumin concentration: 3.5-5.5% (w/v)
or 4.5 mg/dl.
Albumin is responsible for
• maintaining osmotic pressure of the blood and
• for the transport of endogenous and
exogenous substances.

8.  As a transport protein for
endogenous ,albumin
complexes with
Free fatty acids ,
Billirubin and various hormones
(such as cortisone , aldosterone ,and thyroxine)
Tryptophan .
 Many weak acidic drugs bind to
albumin by electrostatic and
hydrophobic bonds.

9. Weak acidic drugs such as
• Salicylates, phenylbutazone and penicillin
are highly bound to albumin.
WARFARIN AND
AZAPROPAZINE BINDING SITE
DIAZEPAM DIGITOXIN TAMOXIFEN

10. I
Normal Range of Concentrations
Protein Molecular
Weight (Da)
(g/L) (mol/L)
Albumin 65,000 35–50 5–7.5 x 10–4
1-Acid
glycoprotein
44,000 0.4–1.0 0.9–2.2 x 10– 5
Lipoproteins 200,000–
3,400,000
Variable

11.  also called as orosomucoid
 m.wt 44,000.
 Binding by Hydrophobic bonds
E.g. : Basic Drugs:
Imipramine
Amytriptyline
Lidocaine
nortriptyline
Propranolol
Quinidine and disopyramide

12. GLOBULIN SYNONYM BINDS TO
1. α1 Globulin Transcortine
/Corticosteroid
Binding globulin
Steroidal drugs,
Thyroxin &
Cyanocobalamine.
2. α2 Globulin Ceruloplasmine Vitamin A,D,E,K.
3. β1Globulin Transferine Ferrous ions
4. β2Globulin --- Carotinoids
5. γ Globulin --- Antigens

13. Binding by hydrophobic bond , non
competitive
M.wt ; 2-3 lakhs to 34 lakhs
Bound drug dissolve in lipid core
Lipid core composed of
• Inside ;triglycerides,cholesterol esters
• Outside;apoprotein
CHYL
eg.;
OMIC
VLDL
RONS
• acidic ;diclophenac
• Neutral;cyclosporin-a
• Basic;chlorpromazine
LDL HDL

14. 40 % of Blood comprises of blood cells
Majority is RBCs: 500 times more
diameter as Albumin.
RBC Components that binds to drug:

15. HB
• 7-8 times conc. of albumin
• Binds to pheytoin, peobarbitol,
phenothiazine
CARBONIC
ANHYDRASE
• Binds to ;acetazolamide,chlorthalidine
CELL
MEMBRANE
• Binds to ;imipramine,chloropromazine

16.  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.
 The plasma protein bound drug does not
diffuse easily therefore less extensively
distributed to tissues.
 Drugswith low plasma protein binding have
larger (unbound or free drug
fraction)generally diffuse more easily into
tissues have greater volume of distributions
.

17. 1) THE DRUG
• Physicochemical properties of the drug
lipophilicity protein binding.
cloxicillin is higher lipophilicity which is
95% bound
amoxicillin which is less lipophilic ,
just 20% bound to proteins
• DRUG PROTEIN –TISSUE AFFINITY
Lidocaine has greater affinity for
AAG then HSA
Digitoxin has more affinity for cardiac
muscle than those of skeletal muscle.
Iophenoxic acid ,radiopaque medium has
greater affinity to plasma proteins

18. 2) DRUG INTERACTIONS
 Competion for the drug by other
substances at a protein-binding site
 When 2 drugs or more can bind to same
site , competition between them for
interaction with the binding site results.
 Drug A binds to plasma protein,then
adminster another drug (drug B) having
affinity for the same site results in
displacement of drug A from its site.

19. Such a drug -drug interaction for
combined site is called as displacement
interaction.
Warfarin and phenylbutazone have same
affintiy for HSA
Administered phenylbutazone to a patient
to warfarin therapy results in displacement
of latter from its binding site .
The free warfarin causes adverse
hemorrhagic reactions which may be fatal.

20. Alb. Has more.
Tamoxifen & Dicumarol binds to 10 &
20 sites of alb.
Indomethacine binds to 30 site

21. FFA competes with HSA.
Free FFA level increased during
conditions :
 Physiological C. (Fasting)
 Pathological C. (Diabetes, M.I)
 Pharmacological (Heparin & Caffeine
adm.).
Acidic Drug displaces : Bilurubine from
Alb. & results in Kernictarus.

22. AGE
Neonates: Low Alb. content: more free drug.
Young Infants: High dose of Digoxine due to
large renal clearance.
Elderly: Low Alb. : so more free drug.

24. P =protein, d=drug,
then applying law of mass action to reversible protein
drug binding

p+d <=> pd
(pd)
ka = (p)(d)
pd =ka(p)(d)
 P=concentration of protein
 Pd=concentration protein drug complex
 Ka=association constant
 Kd=dissociation constant

25. Ka>>kd indicates forward reaction i.e protein drug binding
is favoured .
Pt =total conc.of protein ,bound and unbound
Pt =(pd) + (p)
then r = total number of moles drug that bound to protein
r = (pd)/(pt)
= (pd)/(pd)+(p)
Substuting the value of (pd)from the 2- equation
r = ka(p)(d)/ka(p)(d)+(p)
= ka(d)/ka(d)+1
 The above equation holds when there is only one binding
site on the on the protein and protein –drug complex ratio
1:1
 If more then one or N number of binding sites are avalible
per mole of the protein then
r = n ka(d)/ka (d)+1

27. ABSORPTON
SYSTEMIC SOLUBILITY OF DRUGS
DISTRIBUTION
ELIMINATION
KERNICTERUS
THERAPY AND DRUG TARGETING

28. The absorption equilibrium is attained by
transfer of free drug from the site of
administration into the systemic circulation
and when the concentration in these two
compartments become equal.
However ,binding of the absorbed drug to
plasma proteins decreases free drug
concentration and disturbs such an
equilibrium.

29. Thus , sink conditions and the
concentration gradient are reestablished
which now act as the driving force for
further absorption.
This is particularly useful incase of ionized
drugs which are transported with difficulty.

30. Water insoluble drugs ,neutral endogenous
macromolecules such as Heparin
Oil soluble vitamins are circulated and
distributed to tissues by binding
especially to lipoproteins which act as a
vehicle for such hydrophobic compounds.

31.  Plasma protein binding restricts the entry of drugs
that have specific affinity for certain tissues .
 This prevents accumulation of large fraction of
drugs in such tissues and thus,subsqent toxic
reactions.
 plasma protein binding thus favors uniform
distribution of drugs throughout the body by its
buffer function
 A protein bound drug in particular does not cross
the BBB ,the placental barrier and the glomerulus.

32.  Only the unbound drug is capable of being
eliminated.
 This is because the drug protein complex cannot
penetrate into the liver .
 The large molecular size of the complex also
prevents it from getting filtered through the
glomerulus .
 Thus, drugs which are more than 95% bound are
eliminated slowely i.e they have long eliminaton half
lives ;for eg tertacycline ,which is only 65% bound
,has an elimination half life of 8.5 hours in
comparision to 15.1 hours of doxycycline which is
93% bound to plasma proteins .

33. However penicillin have short halves–lives
despite being extensively bound to plasma
proteins .
This is because rapid equilibration occurs
between the free and the bound drug and
the free drug is equally rapidly excreted by
active secretion in renal tubules.

34.  The binding of drugs to lipoproteins can be used for
site specific delivery of hydrophilic moieties.
 This is particularly useful in certain cancer therapys
because certain tumor cells have greater affinity to
for LDL then normal cells.
 Thus binding a suitable antineoplastic to it can be
used as therapetic tool.
 Estradiol binds selectively and strongly to prostrate
and thus prostate cancer can be treated by
attaching nitrogen mustered to estradiol for
targeting of prostate glands.

35. All pharmacokinetic parameters can be
influenced by protein binding.
Bound drug cannot penetrate through
blood capillaries, so that the bound drug
pharmacologically inert.
Plasma–protein bound drug have longer
elimination half lives compare to the
free drug.

36. Protein bound drug doesn’t cross BBB and
placental barrier .
Estradiol binds selectively and strongly to
prostate and thus prostate cancer treated
by attaching nitrogen mustard to estradiol
for targeting of prostate glands.

37. Leon shargel
Gibaldi
Science direct
Wisegeek
Answers .com
Pub med

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