DRUG
INTERACTIONS

M.PHARM 1ST YEARS(2ND SEM)

DEPT. OF PHARMACEUTICS

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CONTENTS

 INTRODUCTION

 PROTEIN BINDING INTERACTION

 TISSUE BINDING INTERACTION

 CYTOCHROME p-450 BASED DRUG INTERACTION

 DRUG INTERACTION LINKED TO TRANSPORTERS

 REFERENCES

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INTRODUCTION

 Drug interaction are said to occur when the
pharmacological action of a drug altered by the
concomitant use of another drug or by presence of other
substance.

 The drug whose activity is affected by such an interaction is
called as the object drug and the agent which precipitants
such an interaction is referred to as the precipitant.

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PROTEIN BINDING

INTERACTION

 The interacting molecule 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

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Cont…

 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 maybe divided into

Intracellular binding.

Extracellular binding.

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MECHANISM OF PROTEIN –

DRUG BINDING

 Binding of drugs to proteins is generally of reversible &
irreversible.

 Reversible generally involves weak chemical bond such as :

Hydrogen bonds

Hydrophobic bonds

Ionic bonds

Van der Waal’s forces

 Irreversible drug binding, through rare, arises as a result of
covalent binding and is often a reason for the

www.cDualoMricx.cionmogenicity or tissue toxicity of a drug.

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BINDING OF DRUG TO
BLOOD COMPONENTS

A.PLASMA PROTEIN-DRUG BINDING:-

The binding of drugs of plasma proteins is reversible.

The extent or order of binding of drug to plasma protein is

Albumin >α1-Acid Glycoprotein >Lipoproteins >Globulins

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BINDING OF DRUGS TO

HUMAN SERUM ALBUMIN

 It is the most abundant plasma protein (59%) having mol.wt
of 65,000 Daltons with large drug binding capacity.

 Both endogenous compounds such as fatty acids, bilirubin as
well as drug binds to HSA(Human Serum Albumin).

 Four different sites on HSA for drug binding.

Site I : Warfarin & azapropazone binding site.

Site II : Diazepam binding site.

Site III: Digitoxin binding site.

Swwiwt.eDu loIMVix.c:o mTamoxifen binding site

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CONT…

BINDING OF DRUG TO α1 –ACID
GLYCOPROTEIN(Orosomucoid)

➢ It has a m.wt of 44,000 dalton and plasma conc. Range of
0.04 to 0.1g%.

➢ Its binds to basic drugs like
imipramine,lidocaine,propranolol,quinidine.

BINDING OF DRUG TO LIPOPROTEINS:

❖ Binding by : hydrophobic bonds ,Non-competitive.

❖ Mol.wt: 2-34 lacks dalton.

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CONT…

❖ Lipid core composed of:

Inside: Triglyceride & Cholesteryl esters.

Outside: Apoprotein.

Example:

Acidic: Diclofenac

Neutral:Cyclosporin

Basic: Chlorpromazine

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A.BINDING OF DRUG TO

GLOBULINS:

GLOBULIN SYNONYM BINDS TO

α1 Globulin Transcortine,cortico Steroidal drugs ,
steroid binding Thyroxin&
globulin Cyanocobalamine.

α2 Globulin Ceruloplasmine Vitamin A,D,E,K.

β1 Globulin Transferin Ferrous ions

β2 Globulin —– Carotinoids

γ Globulin —– Antigens
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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 and extent of entry into RBC is more for liphophilic
drugs.

 The RBC comprises of 3 components.

1. Haemoglobin: It has m.wt of 64,500 daltons.drugs
like phenytoin,pentobarbital bind to haemoglobin.

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2.Carbonic anhydrase: Carbonic anhydrase inhibitors drugs
are bind to it like acetazolamide & chlorthalidone.

3.Cell membrane: Imipramine & chlorpromazine are reported
to bind with the RBC membrane.

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BINDING OF DRUG TO 14

EXTRAVASCULAR TISSUE
PROTEIN

Importance :

 It increases apparent volume of distribution of drugs.

 Localization of a drug at specific site in body.

Factors affecting:

 Lipopilicity, structural feature of drug, perfusion rate, pH
differences.

 Binding order: liver >kidney >lung >muscles
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TISSUE BINDING OF

1.Liver Irreversible binding of epoxides of Halogenated
Hydrocarbon & Paracetamol.

2.Lungs Basic drugs:
Imipramine,Chlorpromazine,Antihistaminics.

3.Kidney Metallothionin protein binds to Heavy metals
&results in renal accumulation and toxicity.

4.Skin Chloroquine &Phenothiazine binds to melanin.

5.Eye Chloroquine & Phenothiazine also binds to eye
melanin & results in retinopathy.

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TISSUE BINDING OF

6.Hairs Aresenicals,Chloroquine & Phenothiazine.

7.Bones Tetracyclines (yellow discoloration of teeth).

8.Fats Lipophilic drugs (Thiopental),Pesticides(DDT)

9.Nucleic Chloroquine & Quinacrine
Acid

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PLASMA PROTEIN DRUG BINDING TISSUE DRUG BINDING 17
s

1)Binding involves weak bonds and thus Binding generally involves strong bonds
reversible and irreversible.

2)Small apparent volume of distribution Large apparent volume of distribution

3)Half life short Half life long

4)Competitive binding Non-competitive binding

5)Does not result in toxicity Tissue toxicity

6)Displacement possible Displacement does not occur

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FACTORS AFFECTING PROTEIN 18

DRUG BINDING

DRUG RELATED FACTORS

A.Physiochemical characteristic 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:-
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CONT…

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 protein as
compared to that of proteins of skeletal muscles or those in
the plasma like HSA.

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PROTEIN TISSUE

RELATED FACTORS

A.Physicochemical characteristic 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.

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CONT…

B.Concentration of Protein / Binding component:

 Among the plasma protein ,binding predominantly occurs
with albumin, as it is present in high concentration in
comparison to other plasma protein.

 The amount of several proteins and tissue components
available for binding,changes during disease states.

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DRUG INTERACTION

A.Competition Between Drugs for the Binding Sites
(Displacement Interactions):-

D1 + P → D2 + P

D1 – Displacement of Drug D2-Displacer Drug

e.g:- Administration of Phenylbutazone to a patient on Warfarin
therapy results in Haemorrhagic reaction.

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CONT…

B.Competition Between Drugs & Normal Body
Constituents:-

 The free fatty acids are known to interact with a number of
drugs that binds primarily to HSA.

 The free fatty acid level increases in physiological &
pathological condition.

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C.Allosteric changes in protein molecule:-

 The process involves alteration of the protein structure by the
drug or its metabolite thereby modifying its binding capacity.

 (e.g.)Aspirin acetylates lysine fraction of albumin thereby
modifying its capacity to bind NSAIDs like Phenylbutazone
(Increased Affinity) & flufenamic acid (Decreased Affinity).

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PATIENT-RELATED

FACTORS

1.Age:

 Neonates: Low albumin content

 Young infants: High dose of Digoxin due to large renal
clearance.

 Elderly :Low albumin .So More free drug.

2.Intersubject Variability: Due to Genetics & Environmental
factors.

3.Disease States:

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DISEASE INFLUENCE ON INFLUENCE ON 26
DPILSAESAMASE STATPEROSTEIN DRUG

PROTEIN BINDING

Renal Failiure ↓se Albumin ↓se binding of acidic
content drugs; Neutral & basic

drugs are unaffected.

Hepatic Failiure ↓se Albumin ↓se binding of acidic drugs
synthesis & binding of basic drug is

normal or
↓se depending on AAG
Levels.

Inflammatory ↑se AAG Levels ↑se binding of basic drugs;
states i.e,truama neutral and acidic drugs
surgery etc… are unaffected.

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SIGNIFICANCE OF PROTEIN
/TISSUE BINDING OF DRUG

1.Absorption:-

 As we know the conventional dosage form follow first order
kinetics.so when there is more protein binding then it
disturbs the absorption equilibrium.

2.Distriburtion:-

 A protein bound drug in particular dose not cross the BBB,
the Placental Barrier,the Glomerulus.

 Thus protein binding decreases the distribution of drugs.

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CONT…

3.Metabolism:-

 Protein binding decreases the metabolism of drugs &
enhances the biological half life.

 Only unbound fraction get metabolized.

 E.g.Phenylbutazone & Sulfonamide.

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CONT…

4.Elimination:-

 Only the unbound drug is capable of being eliminated.

 Protein binding prevent the entry of drug to the metabolizing organ
(Liver) .

 Large molecular size of complex also prevents it from getting
filtered through glomerulus.

 e.g. Tetracycline is eliminated mainly by glomerular filteration.

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5.Systemic solubility of drug:-

 Lipoprotein act as vehicle for hydrobpobic drugs like
Steroids,Heparin,Oil soluble Vitamin.

6.Drug action:-

 Drug binding inactivates the drugs because sufficient
concentration of drug can not be build up in the receptor site
for action.

 e.g: Naphthoquinone

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7.Sustain Release:-

 The complex of drug protein in the blood act as a reservoir &
continously supply the free drug.

 E.g: Suramin sodium-protein binding of antitrypanosomal
action.

8.Diagnosis:-

 The chlorine atom of Chloroquine replaced with
Radiolabelled I-131 can be used to visualize-melanomas of
eye & disorders of thyroid gland.

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CYTOCHROME p-450

 Cytochrome p-450 is a superfamily of MonoOxygenases.

 Heme-containing enzymes or hemoproteins.

 Officially abbreviated as CYP

 Is a large and diverse group of enzymes that catalyze the
oxidation of organic substances

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CYTOCHROME p-450 BASED

INTERACTION

 Several factors directly or indirectly influence the CYP activity.

 Many drug interaction as a result of induction or inhibition of CYP
enzymes.

 Enzyme Inhibition:

 A drug may inhibit the CYP isoenzyme whether or not it is a
substrate for that isoenzyme.

 If the the two drug are the substrate for the same CYP isoenzyme
then metabolism of one or the both the drugs maybe delayed.

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CONT…

Examples:

 Erythromycin and Midazolam both are substrates for 3A4
isoenzyme so, there is competition for enzyme sites and
metabolism of midazolam is inhibited.

 Fluoroquinolones ,Antimicrobial and azole Antifungal
although not metabolised by CYP3A4 isoenzyme,cause
rapid reversible inhibition of CYP3A4 isoenzyme.

 Cimetidine,Amidarone and Stiripentol are nonspecific
inhibitors of CYP450 enzyme system.

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ENZYME INDUCTION

 Exposure to environmental pollutants as well as large number
of lipophilic drugs can result in induction of CYP enzymes.

 The most common mechanism is transcriptional activation
leading to increased synthesis of more CYP enzymes proteins.

 If drug induces own metabolism ,it is called Autoinduction.

 Example : Carbamazepine

 If induction is by other compounds is called foreign induction.

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 Metabolism of the affected drug is increased leading to
decreased intensity and duration of drug effects.

Isoenzymes:-

 Isoenzyme responsible for the total body clearance of a drug.

 Induction or inhibition of these isoenzymes leads to clinically
significant drug interaction.

For example:3A,2D6,IA2,2C9,2C19,2E1Isoenzymes

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DRUG INTERACTION INVOLVING

CYP3A4 ISOENZYMES
INHIBITORS EXAMPLES DRUGS AFFECTED

(substrates)

Azole antifungal Fluconazole Terfenadine
Ketoconazole Triazolam

Macrolide antimicrobials Erythromycin Carbamazepine
Clarithromycin Cyclosporin

SSRI Fluoxitine Diazepam
Paroxitine Alprazolam

CCB Verapamil Carbamazepine
Ditiazem Cyclosporin

Inducers Rifampicin Diazepam
Rifabutin Protease inhibitors

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DRUG INTERACTION INVOLVING

CYP2D6 ISOENZYMES

INHIBITORS EXAMPLE DRUG AFFECTED
(substrates)

CYP206- Fluoxetine Imipramine
SSRI Cimetidine Propranolol

CYP1A2 Ciprofloxacin Caffeine
Cimetidine Theophylline

CYP2C9 Fluconazole Phenytoin
Cimetidine

CYP2C19 Omeprazole Diazepam
Ketoconazole Omeprazole

CYP2E1 Disulfiram chloroxazone
isoniazid

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OTHER FACTORS

AGE:-

➢ Activity of CYP enzymes decreases with advancing age in both
the sexes.

➢ In-vivo activities of CYP1A2,3A4,2C9 & 2D6 have been
reported to be low at birth , but maximally increased at the young
adult stage and decreased at old age.

GENDER:-

➢ Women exhibit higher baseline 3A4 activity than men and
therefore a great extent of interaction on average.

➢ Diazepam & prednisolone clearance is more in women.
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Propranolol clearance is more in men.

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Cont…

HORMONES:-

 Testosterone deficiency decreases CYP activity.

 Estrogen has been found to decrease the oxidation of some drugs

 E.x:-Imipramine.

 Growth hormone deficiency may lead to down regulation of CYP
enzymes.

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CONT…

GENETIC POLYMORPHISM:-

 Genetic polymorphism with clinical implication has been
described for 2D6,2C19,2C9 & 1A2.These isoenzymes
exhibit polymorphism with number of allelic variants,the
frequency of which often varies between different
populations.

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Cont…

HEPATIC DISEASE:-

 In Cirrhotic patients expression of 1A2,2E1, AND 3A
isoenzymes was decreased.

INFLAMATION:-

 Tumour necrosis factor and interleukin 1 , two major
inflammatory cytokines probably play a role.these factor have
been reported to inhibit CYP enzymes in rates and mice.

 Acute phase response inflammatory mediators have been
reported to supress CYP activity in humans.
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Cont…

 NUTRITION:-

 Obesity has been reported to increase metabolism of enflurane
and sevoflurane in humans.

 ENVIROMENTAL FACTORS:-

 Cigarette smoking is known to induce CYP enzymes.

 PREGNANCY:-

 Increased metabolism of metoprolol was found in pregnant
women due to induction of 2D6 isoenzyme.

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DRUG INTERACTION

LINKED TO TRANSPORTERS

 Transporters should be an integral part of any ADMET
modelling program.

 Transporter mediated drug-drug interaction may cause
unexpected toxicities.

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EXAMPLES OF TRANSPORTER-

MEDIATED DRUG INTERACTIONS
INTERACTING AFFECTED CONSEQUENCE FOLD CHANGES
DRUG DRUG IN SUBSTRATE

PLASMA AUC

Quinidine Digoxin Digoxin exposure 1.7-fold P- gp ,MDR1
↑se Inhibition.

Rifampin Digoxin Digoxin exposure P- gp Induction.
30%↓se

Probenecid Cephradine Cephradine exposure 3.6- OAT Inhibition.
fold ↑se

Cimetidine Metformin Metformin exposure 1.4-fold OCT Inhibition.
↑se

Cyclosporine Rosuvastatin Rosuvastatin exposure 7-fold OATP Inhibition &
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PREDICTING DRUG-DRUG

INTERACTIONS

 By understanding which enzymes or transporters maybe be
involved in the ADME process and the potential for a drug to
be a substrate , inhibitors or inducer of that process ,we can
predict the potential for drug interactions.

 For e.x. Rosuvastatin – Cyclosporine Interaction

 Cyclosporine ↑se 7 fold exposure of Rosuvastatin.

 Possible mechanism of inhibition by Cyclosporine

 OATP1B1/1B3 (Uptake transporter)

 BCRP (Efflux transporter)

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OATP,BCRP-BASED

INTERACTION

 Cyclosporine inhibits other OATP or BCRP substrates

E.g:Pitavastatin is a substrate of OATP1B1/1B3 and BCRP

 Cyclosporine ↑se Pitvastatin exposure 4.6-fold.

 Rosuvastatin is inhibited by other OATP or BCRP
inhibitors

 Lopinavir /Ritonavir ↑se Rosuvastatin exposure 2-fold

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REFERENCES

 Brahmankar D.M. and Jaiswal S.B.(2009) Biopharmaceutics
and Pharmacokinetics: A treatise,2nd edition.,vallabah
prakashan,Pg.no:116-136.

 Shargel L. and Andrew B.C.(2005) Applied Biopharmaceutics
and Pharmacokinetics,5th edition,Mc Graw Hill
company,Pg.no:267-298.

 Cytochrome p450 and Drug Interactions by D.K Badyal ,
A.P.Dadhich ( Indian Journal of Pharmacology 2001;
33:Pg.no:248-259)

 Slideshare-Transporter Mediated Drug-Drug Interaction by
Lei Zhang,Ph.D.(USFDA)

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THANK YOU

FOR YOURS
KIND ATTENTION
AND PATIENCE ☺

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