effect of protein binding interaction

1. DRUG INTERACTION
Effect of protein binding interaction
PRESENTED BY:
V. SENTHILKUMAR, M.PHARM.,(Ph.D).,
K P College of pharmacy,
Tiruvannamalai.

2. 



 Introduction
 Pharmacokinetics
 Toxicokinetics
Drug Interactions
1) Pharmacokinetic Interactions
2) Pharmacodynamic Interactions
Protein – Drug Binding Interactions
1) Binding of drug to blood components
a) Plasma Proteins
b) Blood cells
2) To Extra vascular Tissues
a) Proteins
b) Fats
c) Bones
Factors Affecting Protein Drug Binding
References
CONTENTS

3. 1. INTRODUCTION
Pharmacokinetics, is the study of the absorption, distribution, metabolism, and excretion of
xenobiotics. Xenobiotics are substances that are foreign to the body and include natural or
synthetic chemicals, drugs, pesticides, environmental agents, and industrial agents. Mathematical
models and equations are used to describe and to predict these phenomena.
 It refers on how the body acts on the drug and involves the study of absorption, distribution,
metabolism (biotransformation) and drug excretion
 Toxicokinetics, which is analogous to pharmacokinetics, is the study of the absorption,
distribution, metabolism, and excretion of a xenobiotic under circumstances that produce toxicity.
 Toxicokinetics describes how the body handles a toxicant, as a function of dose and time, in
terms of ADME

4. 2. DRUG INTERACTIONS
Drug interaction is defined as the pharmacological activity of one drug is altered by the
concominant use of another drug or by the presence of some other substance.
OR
 It is the modification of the effect of one drug (the object drug ) by the prior concomitant
administration of another (precipitant drug).
The Drug whose Activity is effected by such an interaction is called as a “Object drug.”
The agent which precipitates such an interaction is referred to as the “Precipitant”.
 Concomitant use of several drug in presence of another drug is often necessory for achiving a
set of goal or in the case when the patient is suffering from more than one disease.
 In these cases chance of drug interaction could increase.

5. Outcomes Of Drug Interactions
1) Loss of therapeutic effect
2) Toxicity
3) Unexpected increase in pharmacological activity
4) Beneficial effects
e.g. additive & potentiating (intended) or antagonism (unintended).
5) Chemical or physical interaction
e.g. I.V incompatibility in fluid or syringes mixture
Mechanisms Of Drug Interactions
Pharmacokinetic Pharmacodynamic
 Pharmacokinetics involve the effect of a drug on another drug kinetic that includes absorption,
distribution , metabolism and excretion.
 Pharmacodynamics are related to the pharmacological activity of the interacting drugs
E.g., synergism , antagonism, altered cellular transport effect on the receptor site.

6. 1) Altered GIT absorption
•Altered pH
•Altered bacterial flora
• formation of drug chelates or complexes
• drug induced mucosal damage
• altered GIT motility.
a) Altered pH;
The non-ionized form of a drug is more lipid soluble and more readily
absorbed from GIT than the ionized form does.

7. Ex1.,
antacids Decrease the tablet dissolution
of Ketoconazole (acidic)
Therefore, these drugs must be separated by at least 2h in the time of administration of both .
b) Altered intestinal bacterial flora;
EX., 40% or more of the administered digoxin dose is metabolised by the intestinal flora.
Antibiotics kill a large number of the normal flora of the intestine
Increase digoxin concentration
and increase its toxicity

8. c) Complexation or chelation;
EX1., Tetracycline interacts with iron preparations
Ex2. Antacid (aluminum or magnesium hydroxide)
Decrease absorption of
ciprofloxacin by 85%
due to chelation
d) Drug-induced mucosal damage:
Antineoplastic agents
(cyclophosphamide, vincristine, procarbazine)
Inhibit absorption
of several drugs
eg., digoxin

9. e) Altered motility
Metoclopramide (antiemitic)
Increase absorption of cyclosporine
due to the increase of stomach empting
time and Increase the toxicity of
cyclosporine
f) Displaced protein binding
It depends on the affinity of the drug to plasma protein. The most likely bound drugs is capable
to displace others. The free drug is increased by displacement by another drug with higher
affinity.
 Phenytoin is a highly bound to plasma protein (90%), Tolbutamide (96%), and warfarin (99%)
and Drugs that displace these agents are Aspirin, Sulfonamides, phenylbutazone.

10. g) Altered metabolism
 The effect of one drug on the metabolism of the other is well documented. The liver is the
major site of drug metabolism but other organs can also do e.g., WBC, skin, lung, and GIT.
 CYP450 family is the major metabolizing enzyme in phase I (oxidation process). Therefore,
the effect of drugs on the rate of metabolism of others can involve the following examples.
Ex. Enzyme induction
 A drug may induce the enzyme that is responsible for the metabolism of another drug or even
itself
Ex. 1) Carbamazepine (antiepileptic drug ) increases its own Metabolism.
2) Phenytoin increases hepatic metabolism of theophylline leading to decrease its level Reduces
its action and Vice versa
Ex. Enzyme inhibition;
 It is the decrease of the rate of metabolism of a drug by another one.
 This will lead to the increase of the concentration of the target drug and leading to the increase
of its toxicity .
Inhibition of the enzyme may be due to the competition on its binding sites , so the onset of
action is short may be within 24h.
 When an enzyme inducer ( e.g. carbamazepine) is administered with an inhibitor (verapamil).
The effect of the inhibitor will be predominant

11. h) Renal excretion:
i. Active tubular secretion
It occurs in the proximal tubules. The drug combines with a specific protein to pass through
the proximal tubules.
When a drug has a competitive reactivity to the protein that is responsible for active transport
of another drug .This will reduce such a drug excretion increasing its concentration and hence its
toxicity increases.
EX. Probenecid decreases tubular secretion of methotrexate.
ii. Passive tubular reabsorption;
Excretion and reabsorption of drugs occur in the tubules By passive diffusion which is
regulated by concentration and lipid solubility.
Ionized drugs are reabsorbed lower than non-ionized ones.
Ex1. Sodium bicarbonate
Ex2. Antacids
Increases lithium clearance
and decreases its action
Increases Salicylates clearance and
decreases its action

12. Synergistic or additive effect
change in its serum concentration by
ii) Pharmacodynamic Interaction
It means alteration of the dug action without
pharmacokinetic factors.
EX., Propranolol + verapamil
Additive effect : 1 + 1 =2
Synergistic effect : 1 +1 > 2
Potentiation effect : 1 + 0 =2
Antagonism : 1-1 = 0
 Receptor interaction
•Competitive
•Non-competitive
 Sensitivity of receptor
•Number of receptor
•Affinity of receptor
 Alter neurotransmitter release /drug transportation
 Alter water/electrolyte balance

13. 3. Protein – Drug Binding Interactions
 The interacting molecules are generally the macromolecules such as protein, DNA or adipose.
The protein are particularly responsible for such an interaction.
The phenomenon of complex formation of drug with protein is called as protein binding of
drug.
 As a protein bound drug is neither metabolized nor excreted hence it is pharmacologically
inactive due to its pharmacokinetic and Pharmacodynamic inertness.
Protein + drug ⇌ Protein-drug complex
 Protein binding may be divided into:
1. Intracellular binding.
2. Extracellular binding

14. Mechanisms Of Protein Drug Binding:
 Binding of drugs to proteins is generally of reversible &irreversible.
 Reversible generally involves weak chemical bond such as:
1. Hydrogen bonds
2. Hydrophobic bonds
3. Ionic bonds
4. Van der waal’s forces.
•Irreversible drug binding, though rare, arises as a result of covalent binding and is often a reason
for the carcinogenicity or tissue toxicity of the drug.

16. 1. BINDING OF DRUG TO BLOOD COMPONENTS
A. Plasma protein-drug binding:-
 The binding of drugs to plasma proteins is reversible.
 The extent or order of binding of drug to plasma proteins is:
Albumin > α1-Acid glycoproteins > Lipoproteins > Globulins.
1. Binding of drug to human serum Albumin.
 It is the most abundant plasma protein (59%), having M.W. of 65,000 with large drug binding
capacity.
 Both endogenous compounds such as fatty acid, bilirubin as well as drug binds to HSA.
 Four different sites on HSA for drug binding.
Site I: Warfarin & Azapropazone binding site. Ex. Non-Steroidal Anti-Inflammatory Drugs,
Sulphonamides
Site II: Diazepam binding site. Ex. benzodiazepines, medium chain fatty acids, ibuprofen etc.
Site III: Digitoxin binding site.
Site IV: Tamoxifen binding site.

17. 2. Binding of drug to α1-Acid glycoprotein: (Orosomucoid)
It has a M.W. 44,000 and plasma conc. range of 0.04 to 0.1 g%. It binds to no. of basic drugs like
imipramine, lidocaine, propranolol, quinidine.
3. Binding of drug to Lipoproteins:
Binding by: Hydrophobic Bonds, Non-competitive.
Mol wt: 2-34 Lacks Dalton.
Lipid core composed of:
Inside: triglyceride & cholesterol esters.
Outside: Apoprotein.
Ex.
Acidic: Diclofenac.
Neutral: CyclosporineA.
Basic: Chlorpromazine.
Chylomicrons VLDL
HDLLDL
Types

18. 4. Binding Of Drug ToGlobulins
Globulin Synonym Binds to
α1 Globulin Transcortine
/Corticosteroid Binding
globulin
Steroidal drugs, Thyroxin
& Cyanocobalamine.
α2 Globulin Ceruloplasmine Vitamin A,D,E,K.
β1 Globulin Transferin Ferrous ions
β1 Globulin ------ Carotenoids
γ Globulin ------ Antigens

19. B. Binding Of Drug To Blood Cells
 In blood 40% of blood cells of which major component is RBC (95%). The RBC is 500 times
in diameter as the albumin. The rate & extent of entry into RBC is more for lipophilic drugs.
 The RBC comprises of 3 components.
a)Haemoglobin: It has a M.W. of 64,500 Dal. Drugs like Phenytoin, pentobarbital bind to
haemoglobin.
b) Carbonic anhydrase: Carbonic anhydrase inhibitors drugs are bind to it like acetazolamide &
chlorthalidone.
c) Cell membrane: Imipramine & chlorpromazine are reported to bind with the RBC membrane.
2. BINDING OF DRUG TO EXTRAVASCULAR TISSUE PROTEIN
Importance: 1. It increases apparent volume of distribution of drug.
2. localization of a drug at a specific site in body.
 Factor affecting: lipophilicity, structural feature of drug, perfusion rate, pH differences.
Binding order: Liver › Kidney › Lung › Muscles

20. Tissue Binding of
Liver Irreversible binding of Epoxides of
Halogenated Hydrocarbon & Paracetamol.
Lungs Basic drugs: Imipramine, Chlorpromazine,
& Antihistamines.
Kidney Metallothionin protein binds to Heavy metals
& results in Renal accumulation and toxicity.
Skin Chloroquine & Phenothiazine bindsto
Melanin.
Eye Chloroquine & Phenothiazine also bindsto
Eye Melanin & results in Retinopathy.
Hair Arsenicals, Chloroquine, & Phenothiazine.
Bones Tetracycline(yellow discoloration of teeth),
Lead(replaces Ca & cause brittleness)
Fat Lipophilic drugs (thiopental), Pesticides
(DDT)
Nucleic acid Chloroquine & Quinacrine.

21. 4. Factors Affecting Protein Drug Binding
1. Drug-related factors
a. Physicochemical characteristics of the drug:-
 Protein binding is directly related to the lipophilicity of drug. An increase in lipophilicity
increases the extent of binding.
b. Concentration of drug in the body:-
 Alteration in the concentration of drug substance as well as the protein molecules or surfaces
subsequently brings alteration in the protein binding process.
c. Affinity of a drug for a particular binding component:-
 This factor entirely depends upon the degree of attraction or affinity the protein molecule or
tissues have towards drug moieties.
 For Digoxin has more affinity for cardiac muscles proteins as compared to that of proteins of
skeletal muscles or those in the plasma like HSA.

22. 2. Protein/ tissue related factors:
a. Physicochemical characteristics of protein or binding agent:
 Lipoproteins & adipose tissue tend to bind lipophilic drug by dissolving them in their lipid
core.
The physiological pH determines the presence of active anionic & cationic groups on the
albumin to bind a variety of drug.
b. Concentration of protein or binding component:
 Among the plasma protein , binding predominantly occurs with albumin, as it is present in high
concentration in comparision to other plasma protein.
The amount of several proteins and tissue components available for binding, changes during
disease state.

23. 3. Drug interactions
a. Competition between drugs for the binding sites[ Displacement interactions]:-
D2
D1+P
D1: Displaced drug.
D2+P
D2: Displacer drug.
Ex. Administration of phenylbutazone to a patient on Warfarin therapy results in Hemorrhagic
reaction.
b. Competition between drug & normal body constituents:-
The free fatty acids are known to interact with a no. of drugs that binds primarily to HSA. the free
fatty acid level increase in physiological, pathological condition.
c. Allosteric changes in protein molecule:-
The process involves alteration of the protein structure by the drug or it’s metabolite thereby
modifying its binding capacity.
Ex. aspirin acetylates lysine fraction of albumin thereby modifying its capacity to bind NSAIDs
like phenylbutazone.

24. 4. Patient-related factors
a. Age:
1. Neonates: Low albumin content: More free drug.
2. Young infants: High dose of Digoxin due to large renal clearance.
3. Elderly: Low albumin: So more free drug.
b. Intersubject variability: Due to genetics & environmental factors.
c. Disease states:-
Disease Influence on plasma
protein
Influence on protein drug
binding
Renal failure ↓ Albumin content ↓ binding of acidic drugs;
neutral and basic drugs are un
affected
Hepatic failure ↓ Albumin synthesis ↓ binding of acidic drugs;and
binding of basic drugs is
normal or
↓ depending on AAG levels
Inflammatory states i.e.,
trauma surgery etc…
↑AAG levels ↑ binding of basic drugs;
neutral and acidic drugs are un
affected

25. 5. REFERENCES
1. Brahmankar D.M. and Jaiswal S.B.(2009) Biopharamaceutics and pharmacokinetics: A
Treatise ,2nd ed. ,Vallabh Prakashan ,p. 116-136.
2.Shargel L.& Andrew B.C.(2005) Applied Biopharamaceutics and pharmacokinetics ,5th ed.,
Mc Graw Hill company ,p. 267-298.
3. Tripati K.D. Essential of Medical pharmacology ,6th ed. , Jaypee brothers Medical publisher
Ltd. ,p. 20-23.
4. Barar F.S.K. Essential of pharmacotherapeutices ,5th ed. S.Chand and Company Ltd. ,p. 43-
48.