Pharmacodynamics (Mechanisn of drug action)

PharmacodynamicsPharmacodynamicsDepartment of Department of PharmacologyPharmacology

NEIGRIHMS, ShillongNEIGRIHMS, Shillong

ContentsContents PRINCIPLES AND MECHANISM OF PRINCIPLES AND MECHANISM OF

DRUG ACTIONDRUG ACTION

TRANSDUCER MECHANISMSTRANSDUCER MECHANISMS

DOSE-RESPONSE RELATIONSHIPDOSE-RESPONSE RELATIONSHIP

COMBINED DRUG EFFECTSCOMBINED DRUG EFFECTS

What is Pharmacodynamics?What is Pharmacodynamics?

What the drug does to the body when What the drug does to the body when it enters?it enters?

Defn.: It is the study of biochemical Defn.: It is the study of biochemical and physiological effects of drug and physiological effects of drug and their mechanism of action atand their mechanism of action at organorgan level as well as level as well as cellularcellular level.level.

PRINCIPLES OF DRUG ACTIONPRINCIPLES OF DRUG ACTION

- Do NOT impart new functions on any Do NOT impart new functions on any system, organ or cellsystem, organ or cell

- Only alter the PACE of ongoing activityOnly alter the PACE of ongoing activity

STIMULATION STIMULATION DEPRESSIONDEPRESSION IRRITATIONIRRITATION REPLACEMENTREPLACEMENT CYTOTOXIC ACTIONCYTOTOXIC ACTION

PRINCIPLE OF PRINCIPLE OF ACTIONACTION

MODEMODE EXAMPLEEXAMPLE

STIMULATIONSTIMULATION Selective Enhancement Selective Enhancement of level of of level of activity of activity of specialised cells specialised cells - Excessive stimulation is often - Excessive stimulation is often followed by depression of that functionfollowed by depression of that function

Pilocarpine stimulates Pilocarpine stimulates salivary glandssalivary glandsPicrotoxin – CNS stimulant Picrotoxin – CNS stimulant convulsions convulsions coma coma death death

DEPRESSIONDEPRESSION Selective Diminution Selective Diminution of activity of of activity of specialised cells specialised cells Certain drugs – stimulate one cell type Certain drugs – stimulate one cell type and depress othersand depress others

Barbiturates depress CNS Barbiturates depress CNS Quinidine depresses HeartQuinidine depresses HeartAch – stimulates smooth Ach – stimulates smooth muscle but depresses SA muscle but depresses SA nodenode

IRRITATIONIRRITATION Non-selective Non-selective often often noxiousnoxious effect – effect – applied toapplied to less specialised cells less specialised cells (epithelium, connective tissue)(epithelium, connective tissue)-stimulate associated function -stimulate associated function

Bitters – salivary and gastric Bitters – salivary and gastric secretionsecretionCounterirritants increase Counterirritants increase blood flow to a site blood flow to a site

REPLACEMENTREPLACEMENT Use of natural metabolites, hormones Use of natural metabolites, hormones or their congeners in or their congeners in deficiency deficiency statesstates

Levodopa in parkinsonismLevodopa in parkinsonismIron in anaemiaIron in anaemia

CYTOTOXIC CYTOTOXIC ACTION ACTION

Selective Selective cytotoxic cytotoxic action for action for invading invading parasites or cancer cellsparasites or cancer cells – – for attenuating them without affecting for attenuating them without affecting the host cellsthe host cells

Penicillin, chloroquinePenicillin, chloroquine

MECHANISM OF DRUG ACTION

MECHANISM OF DRUG ACTIONMECHANISM OF DRUG ACTION

MAJORITY OF DRUGS INTERACT MAJORITY OF DRUGS INTERACT WITH TARGET BIOMOLECULES:WITH TARGET BIOMOLECULES:

Usually a ProteinUsually a Protein 1.1. ENZYMESENZYMES2.2. ION CHANNELSION CHANNELS3.3. TRANSPORTERSTRANSPORTERS4.4. RECEPTORSRECEPTORS

1. Enzymes – drug targets1. Enzymes – drug targets All Biological reactions are carried out under All Biological reactions are carried out under

catalytic influence of enzymes – major drug catalytic influence of enzymes – major drug targettarget

Drugs – increases/decreases enzyme mediated Drugs – increases/decreases enzyme mediated reactionsreactions

In physiological system enzyme activities are In physiological system enzyme activities are optimally setoptimally set

Enzyme stimulation is less common by drugs – Enzyme stimulation is less common by drugs – common by endogenous substratescommon by endogenous substrates– Pyridoxine (cofactor in decarboxylase activity)Pyridoxine (cofactor in decarboxylase activity)– Adrenaline stimulates hepatic glycogen phosphorylase Adrenaline stimulates hepatic glycogen phosphorylase

(hyperglycaemia)(hyperglycaemia) Enzyme inhibition – common mode of drug actionEnzyme inhibition – common mode of drug action

Enzymes – contd.Enzymes – contd. Nonspecific inhibition: Nonspecific inhibition: Denaturation of Denaturation of

proteins – strong acids, heavy metals, proteins – strong acids, heavy metals, alkalies, alcohol, phenols etc.alkalies, alcohol, phenols etc.

Specific Inhibition:Specific Inhibition:

Competitive Noncompetitive

• equilibrium• nonequilibrium

What is specific enzyme inhibition?What is specific enzyme inhibition?

A drug may inhibit A drug may inhibit a particular a particular enzyme without enzyme without affecting others affecting others and influence that and influence that particular particular substrate-enzymesubstrate-enzyme reaction ultimately reaction ultimately to influence in the to influence in the product formationproduct formation

Normal

Drug + Enzyme

Competitive InhibitionCompetitive Inhibition

Enzyme Inhibition - ExamplesEnzyme Inhibition - Examples Equilibrium:Equilibrium:

– Physostigmine Vs Acetylcholine (cholinesterase)Physostigmine Vs Acetylcholine (cholinesterase)– Sulfonamides Vs PABA (folate synthetase)Sulfonamides Vs PABA (folate synthetase)– Moclobemide Vs Catecholamines (MAO-A)Moclobemide Vs Catecholamines (MAO-A)– Captopril Vs Angiotensin 1 (ACE)Captopril Vs Angiotensin 1 (ACE)

Nonequilibrium:Nonequilibrium:– Orgnophosphorous compounds/Nerve gases Orgnophosphorous compounds/Nerve gases

(cholinesterase)(cholinesterase)

Non-competitive:Non-competitive:– Acetazolamide (carbonic anhydrase), Omeprazole Acetazolamide (carbonic anhydrase), Omeprazole

(HKATPase) , Aspirin (cyclooxygenase)(HKATPase) , Aspirin (cyclooxygenase)

Effects of enzyme inhibition:

Normal Competitive (equilibrium)

2. Ion Channnel2. Ion Channnel Proteins take part in transmembrane Proteins take part in transmembrane

signaling and regulates ionic signaling and regulates ionic compositioncomposition

Drugs also target these channels:Drugs also target these channels:– Ligand gated channelsLigand gated channels– G-protein operated channelsG-protein operated channels– Direct action on channelsDirect action on channels

ExamplesExamples

+ +

- -

+ +

--

- -

+ + + +

- -

Na+

+ ++ +

- - - -

Resting (Closed**) Open

(brief)inactivated

Very slow repolarization in presence of LA

LA receptor

LA have highest affinity for the inactivated formRefractory period

LA acting on Na+ receptorsLA acting on Na+ receptors

3. Transporters3. Transporters Substrates are translocated across membrane by Substrates are translocated across membrane by

binding to specific transporters (carriers) – Solute binding to specific transporters (carriers) – Solute Carrier Proteins (SLC)Carrier Proteins (SLC)

Pump the metabolites/ions I the direction of Pump the metabolites/ions I the direction of concentration gradient or against itconcentration gradient or against it

Drugs interact with these transport systemDrugs interact with these transport system Examples: Probenecid (penicillin and uric acid), Examples: Probenecid (penicillin and uric acid),

Furosmide (Na+K+2Cl- cotransport), Furosmide (Na+K+2Cl- cotransport), Hemicholinium (choline uptake) and Vesamicol Hemicholinium (choline uptake) and Vesamicol (active transport of Ach to vesicles)(active transport of Ach to vesicles)

4. Receptors4. Receptors

Drugs usually do not bind directly with enzymes, Drugs usually do not bind directly with enzymes, channels, transporters or structural proteins, but channels, transporters or structural proteins, but act through specific macromolecules – act through specific macromolecules – RECEPTORSRECEPTORS

Definition: Definition: It is defined as a macromolecule or It is defined as a macromolecule or binding site located on cell surface or inside the binding site located on cell surface or inside the effector cell that serves to recognize the signal effector cell that serves to recognize the signal molecule/drug and initiate the response to it, but molecule/drug and initiate the response to it, but itself has no other function,itself has no other function, e.g. G-protein e.g. G-protein coupled receptorcoupled receptor

Some DefinitionsSome Definitions Agonist: Agonist: An agent which activates a receptor to produce an An agent which activates a receptor to produce an

effect similar to a that of the physiological signal molecule, effect similar to a that of the physiological signal molecule, e.g. Muscarine and Nicotine)e.g. Muscarine and Nicotine)

Antagonist:Antagonist: an agent which prevents the action of an agonist an agent which prevents the action of an agonist on a receptor or the subsequent response, but does not have on a receptor or the subsequent response, but does not have an effect of its own, e.g. atropine and muscarinean effect of its own, e.g. atropine and muscarine

Inverse agonist: Inverse agonist: an agent which activates receptors to an agent which activates receptors to produce an effect in the opposite direction to that of the produce an effect in the opposite direction to that of the agonist, e.g. DMCMagonist, e.g. DMCM

Partial agonist: Partial agonist: An agent which activates a receptor to An agent which activates a receptor to produce submaximal effect but antagonizes the action of a produce submaximal effect but antagonizes the action of a full agonist, e.g. pentazocinefull agonist, e.g. pentazocine

Ligand:Ligand: any molecule which attaches selectively to particular any molecule which attaches selectively to particular receptors or sites (only binding or affinity)receptors or sites (only binding or affinity)

Some Definitions – contd.Some Definitions – contd. Affinity:Affinity: Ability of a substrate to bind with Ability of a substrate to bind with

receptorreceptor Intrinsic activity (IA):Intrinsic activity (IA): Capacity to induce Capacity to induce

functional change in the receptorfunctional change in the receptorIf explained in terms of affinity and IA:If explained in terms of affinity and IA: Agonist: Affinity + IA (1)Agonist: Affinity + IA (1) Antagonist: Affinity + IA (0)Antagonist: Affinity + IA (0) Partial agonist: Affinity + IA (0-1)Partial agonist: Affinity + IA (0-1) Inverse agonist: Affinity + IA (0 to -1)Inverse agonist: Affinity + IA (0 to -1)

Drug-receptor binding and Drug-receptor binding and agonismagonism

Drug- Receptor:Drug- Receptor: DRi DRa

DRi DRa

DRi DRa

D

DRi DRa

Full agonist

Partial agonist

Neutral

Inverse agonist

Two State Receptor ModelTwo State Receptor Model

D + RD + R DR ComplexDR Complex

AffinityAffinity – measure of propensity of a – measure of propensity of a drug to bind receptor; the drug to bind receptor; the attractiveness of drug and receptorattractiveness of drug and receptor– Covalent bonds are stable and Covalent bonds are stable and

essentially irreversibleessentially irreversible– Electrostatic bonds may be strong or Electrostatic bonds may be strong or

weak, but are usually reversibleweak, but are usually reversible

Drug - Receptor BindingDrug - Receptor Binding

Affinity

Drug Receptor InteractionDrug Receptor Interaction

Efficacy (or Intrinsic Activity)Efficacy (or Intrinsic Activity) – ability – ability of a bound drug to change the of a bound drug to change the receptor in a way that produces an receptor in a way that produces an effect; some drugs possess affinity effect; some drugs possess affinity but NOT efficacybut NOT efficacy

DR Complex Effect (E)

Receptors – contd.Receptors – contd. Two essential functions:Two essential functions:

– RecognitionRecognition of specific ligand molecule of specific ligand molecule– TransductionTransduction of signal into response of signal into response

Two Domains:Two Domains:– Ligand binding domainLigand binding domain– Effectors Domain – undergoes functional Effectors Domain – undergoes functional

conformational changeconformational change

Receptors – contd.Receptors – contd.

Cell surface receptors remain floated in cell membrane Cell surface receptors remain floated in cell membrane lipidslipids

Functions are determined by the interaction of lipophillic or Functions are determined by the interaction of lipophillic or hydrophillic domains of the peptide chain with the drug hydrophillic domains of the peptide chain with the drug moleculemolecule

Non-polar hydrophobic portion of the amino acid remain Non-polar hydrophobic portion of the amino acid remain buried in membrane while polar hydrophilic remain on cell buried in membrane while polar hydrophilic remain on cell surfacesurface

Hydrophilic drugs cannot cross the membrane and has to Hydrophilic drugs cannot cross the membrane and has to bind with the polar hydrophilic portion of the peptide chainbind with the polar hydrophilic portion of the peptide chain

Binding of polar drugs in ligand binding domain induces Binding of polar drugs in ligand binding domain induces conformational changes (alter distribution of charges and conformational changes (alter distribution of charges and transmitted to coupling domain to be transmitted to transmitted to coupling domain to be transmitted to effector domain effector domain

Receptors – contd.Receptors – contd. Drugs act on Physiological receptors Drugs act on Physiological receptors

and mediate responses of and mediate responses of transmitters, hormones, autacoids transmitters, hormones, autacoids and others – cholinergic, adrenergic and others – cholinergic, adrenergic or histaminergic etc.or histaminergic etc.

Drugs may act on true drug Drugs may act on true drug receptors - Benzodiazepine receptorsreceptors - Benzodiazepine receptors

The Transducer mechanismThe Transducer mechanism Most transmembrane signaling is accomplished

by a small number of different molecular mechanisms (transducer mechanisms)

Large number of receptors share these handful of transducer mechanisms to generate an integrated response

Mainly 4 (four) major categories:1. GPCR2. Receptors with intrinsic ion channel3. Enzyme linked receptors4. Transcription factors (receptors for gene

expression)

G-protein Coupled ReceptorsG-protein Coupled Receptors Large family of cell membrane receptors Large family of cell membrane receptors

linked to the effector linked to the effector enzyme/channel/carrier proteins through enzyme/channel/carrier proteins through one or more GTP activated proteins (G-one or more GTP activated proteins (G-proteins)proteins)

All receptors has common pattern of All receptors has common pattern of structural organizationstructural organization

The molecule has 7 The molecule has 7 αα-helical membrane -helical membrane spanning hydrophobic amino acid spanning hydrophobic amino acid segments – 3 extra and 3 intracellular segments – 3 extra and 3 intracellular loopsloops

GPCRGPCR

GPCR – contd.GPCR – contd.

G-proteins and EffectorsG-proteins and Effectors Large number can be distinguished Large number can be distinguished

by their by their αα-subunits-subunitsG proteinG protein Effector pathway Effector pathway SubstratesSubstrates

GsGs Adenylyl cyclase Beta-receptors, Beta-receptors, H2, D1H2, D1

GiGi Adenylyl cyclase Muscarinic M2Muscarinic M2D2, alpha-2D2, alpha-2

GqGq Phospholipase CPhospholipase C Alph-1, H1, M1, M3Alph-1, H1, M1, M3

GoGo Ca++ channelCa++ channel K+ channel in K+ channel in heart, smheart, sm

GPCR - 3 Major PathwaysGPCR - 3 Major Pathways

1.1. Adenylyl cyclase:cAMP pathwayAdenylyl cyclase:cAMP pathway2.2. Phospholipase C: IP3-DAG Phospholipase C: IP3-DAG

pathwaypathway3.3. Channel regulationChannel regulation

1. Adenylyl cyclase: cAMP pathway1. Adenylyl cyclase: cAMP pathway

PKa Phospholambin

Increased Interaction with Faster relaxationCa++

Troponin

Cardiac contractility

OtherFunctionalproteins

2. Phospholipase C:IP3-DAG 2. Phospholipase C:IP3-DAG pathwaypathway

PKc

3. Channel regulation3. Channel regulation Activated G-proteins can open or close ion Activated G-proteins can open or close ion

channels – Ca++, Na+ or K+ etc.channels – Ca++, Na+ or K+ etc. These effects may be without intervention These effects may be without intervention

of any of above mentioned 2of any of above mentioned 2ndnd messengers messengers – cAMP or IP/DAG– cAMP or IP/DAG

Bring about depolarization, Bring about depolarization, hyperpolrization or Ca ++ changes etc.hyperpolrization or Ca ++ changes etc.

Gs – Ca++ channels in myocardium and Gs – Ca++ channels in myocardium and skeletal musclesskeletal muscles

Go and Gi – open K+ channel in heart and Go and Gi – open K+ channel in heart and muscle and close Ca+ in neuronesmuscle and close Ca+ in neurones

Intrinsic Ion Channel ReceptorsIntrinsic Ion Channel Receptors

Intrinsic Ion Channel ReceptorsIntrinsic Ion Channel Receptors Most useful drugs in clinical medicine act Most useful drugs in clinical medicine act

by mimicking or blocking the actions of by mimicking or blocking the actions of endogenous ligands that regulate the flow endogenous ligands that regulate the flow of ions through plasma membrane of ions through plasma membrane channelschannels

The natural ligands include acetylcholine, The natural ligands include acetylcholine, serotonin, aminobutyric acid (GABA), and serotonin, aminobutyric acid (GABA), and the excitatory amino acids (eg, glycine, the excitatory amino acids (eg, glycine, aspartate, and glutamate)aspartate, and glutamate)

Enzyme Linked ReceptorsEnzyme Linked Receptors 2 (two) types of receptors:2 (two) types of receptors:

1.1. Intrinsic enzyme linked receptorsIntrinsic enzyme linked receptors Protein kinase or guanyl cyclase domainProtein kinase or guanyl cyclase domain

2.2. JAK-STAT-kinase binding receptorJAK-STAT-kinase binding receptor

Enzyme linked receptorsEnzyme linked receptors

Extracellular hormone-binding domain and Extracellular hormone-binding domain and a cytoplasmic enzyme domain (mainly a cytoplasmic enzyme domain (mainly protein tyrosine kinase or serine kinase)protein tyrosine kinase or serine kinase)

Upon binding the receptor converts from Upon binding the receptor converts from its inactive monomeric state to an active its inactive monomeric state to an active dimeric statedimeric state

Cytoplasmic domains become Cytoplasmic domains become phosphorylated on specific tyrosine phosphorylated on specific tyrosine residues residues

Enzymatic activities are activated, Enzymatic activities are activated, catalyzing phosphorylation of substrate catalyzing phosphorylation of substrate proteins proteins

Enzyme linked receptors – contd.Enzyme linked receptors – contd.

Enzyme linked receptors – contd.Enzyme linked receptors – contd. Activated receptors catalyze

phosphorylation of tyrosine residues on different target signaling proteins, thereby allowing a single type of activated receptor to modulate a number of biochemical processes

Examples:Examples:– Insulin - Insulin - uptake of glucose and amino acids and

regulate metabolism of glycogen and triglycerides

– Trastuzumab, antagonist of a such type receptor – used in breast cancer

JAK-STAT-kinase binding receptorJAK-STAT-kinase binding receptor

Mechanism closely resembles that of Mechanism closely resembles that of receptor tyrosine kinasesreceptor tyrosine kinases

Only difference - protein tyrosine kinase Only difference - protein tyrosine kinase activity is not intrinsic to the receptor activity is not intrinsic to the receptor moleculemolecule

Uses Janus-kinase (JAK) familyUses Janus-kinase (JAK) family Also uses STAT (signal transducers and Also uses STAT (signal transducers and

activators of transcription)activators of transcription) Examples – cytokines, growth hormones, Examples – cytokines, growth hormones,

interferones etc.interferones etc.

JAK-STAT-kinase ReceptorsJAK-STAT-kinase Receptors

Receptors regulating gene Receptors regulating gene expressionexpression

Lipid soluble biological signals cross the Lipid soluble biological signals cross the plasma membrane and act on intracellular plasma membrane and act on intracellular receptors – NO acts by stimulating cGMPreceptors – NO acts by stimulating cGMP

Receptors for corticosteroids, Receptors for corticosteroids, mineralocorticoids, thyroid hormones, sex mineralocorticoids, thyroid hormones, sex hormones and Vit. D etc. stimulate the hormones and Vit. D etc. stimulate the transcription of genes in the nucleus by transcription of genes in the nucleus by binding with specific DNA sequence – binding with specific DNA sequence – called - “Responsive elements”called - “Responsive elements”

Receptors regulating gene Receptors regulating gene expression – Clinical implicationexpression – Clinical implication

Hormones produce their effects after Hormones produce their effects after a characteristic lag period of 30 a characteristic lag period of 30 minutes to several hours—the time minutes to several hours—the time required for the synthesis of new required for the synthesis of new proteins – gene active hormonal proteins – gene active hormonal drugs take time to be active drugs take time to be active (Bronchial asthma)(Bronchial asthma)

Beneficial or toxic effects persists Beneficial or toxic effects persists even after withdrawaleven after withdrawal

Receptors regulating gene Receptors regulating gene expressionexpression

Summary of TransducersSummary of Transducers

Receptor RegulationReceptor Regulation Up regulation of receptors:Up regulation of receptors:

– In tonically active systems, prolonged In tonically active systems, prolonged deprivation of agonist (by denervation deprivation of agonist (by denervation or antagonist) results in supersensitivity or antagonist) results in supersensitivity of the receptor as well as to effector of the receptor as well as to effector system to the agonist. Sudden system to the agonist. Sudden discontinuation of Propranolol, Clonidine discontinuation of Propranolol, Clonidine etc.etc.

– Unmasking of receptors or proliferation Unmasking of receptors or proliferation or accentuation of signal amplificationor accentuation of signal amplification

Receptor RegulationReceptor Regulation Continued exposure to an agonist or Continued exposure to an agonist or

intense receptor stimulation causes intense receptor stimulation causes desensitization or refractoriness: receptor desensitization or refractoriness: receptor become less sensitive to the agonistbecome less sensitive to the agonist

Examples – beta adrenergic agonist and Examples – beta adrenergic agonist and levodopalevodopa

Causes:Causes:1.1. Masking or internalization of the receptorsMasking or internalization of the receptors2.2. Decreased synthesis or increased destruction Decreased synthesis or increased destruction

of the receptors (down regulation)of the receptors (down regulation)

DesensitizationDesensitization Sometimes response to all agonists which act Sometimes response to all agonists which act

through different receptors but produce the same through different receptors but produce the same overt effect is decreased by exposure to anyone overt effect is decreased by exposure to anyone of these agonists – heterologous desensitizationof these agonists – heterologous desensitization

Homologous – when limited to the agonist which Homologous – when limited to the agonist which is repeatedly activatedis repeatedly activated

homologousHeterologous

Ach

Hist

Mechanism of desensitizationMechanism of desensitization

ßARK (beta-adrenergic receptor kinase)Beta-arrestin

Dose-Response RelationshipDose-Response Relationship Dose-plasma concentrationDose-plasma concentration Plasma concentration (dose)-Plasma concentration (dose)-

response relationshipresponse relationshipE = E = Emax X [D]

Kd + [D]

E is observed effect of drug dose [D], Emax = maximum response,Kd = dissociation constant of drug receptor complex

Dose-Response CurveDose-Response Curve

doseLog dose

% re

spon

se

% re

spon

se

100%

50%

100%

50%

Dose-Response CurveDose-Response Curve Advantages:Advantages:

– A wide range of drug doses can easily A wide range of drug doses can easily be displayed on a graphbe displayed on a graph

– Potency and efficacy can be comparedPotency and efficacy can be compared– Comparison of study of agonists and Comparison of study of agonists and

antagonists become easierantagonists become easier

Potency and efficacyPotency and efficacy Potency:Potency: It is the amount of drug required to It is the amount of drug required to

produce a certain responseproduce a certain response Efficacy:Efficacy: Maximal response that can be elicited by Maximal response that can be elicited by

a druga drug

Resp

onse

Drug in log conc.

1 2 3 4

Therapeutic index (TI)Therapeutic index (TI)

Therapeutic Index = Therapeutic Index = Median Lethal Dose (LD50)

Median Effective dose (ED50)

Idea of margin of safety Margin of Safety

Therapeutic index (TI)Therapeutic index (TI) It is defined as the gap between therapeutic It is defined as the gap between therapeutic

effect DRC and adverse effect DRC (also called effect DRC and adverse effect DRC (also called margin of safety)margin of safety)

Combined Effects of DrugsCombined Effects of Drugs Drug SynergismDrug Synergism

– Additive effect (1 + 1 = 2)Additive effect (1 + 1 = 2) Aspirin+paracetamol, amlodipine+atenololAspirin+paracetamol, amlodipine+atenolol

– Supraadditive effect (1 + 1 = 4)Supraadditive effect (1 + 1 = 4) Sulfamethoxazole+trimethoprim, Sulfamethoxazole+trimethoprim,

levodopa+carbidopa, acetylcholine+physostigminelevodopa+carbidopa, acetylcholine+physostigmine Drug Abntagonism:Drug Abntagonism:

1.1. Physical: CharcoalPhysical: Charcoal2.2. Chemical: KMNO4, Chelating agentsChemical: KMNO4, Chelating agents3.3. Physiological antagonism: Histamine and Physiological antagonism: Histamine and

adrenaline in bronchial asthma, Glucagons adrenaline in bronchial asthma, Glucagons and Insulinand Insulin

4.4. Receptor antagonismReceptor antagonism

……. Contd. . Contd. Receptor antagonism:Receptor antagonism:

1.1. Competitive antagonism (equilibrium)Competitive antagonism (equilibrium)2.2. Competitive (non equilibrium)Competitive (non equilibrium)3.3. Non-competitive antagonism Non-competitive antagonism

Drug antagonism DRCDrug antagonism DRC

Drug antagonism DRC – non-Drug antagonism DRC – non-competitive antagonismcompetitive antagonism

Resp

ons

e Shift to the right and lowered response

Drug in log conc.

Agonist

Agonist+ CA (NE)

Spare ReceptorSpare Receptor When only a fraction of the total When only a fraction of the total

population of receptors in a cell, are population of receptors in a cell, are needed to produce maximal effect, needed to produce maximal effect, then the cell is said to have spare then the cell is said to have spare receptorsreceptors

Example - Beta-adrenergic blockingExample - Beta-adrenergic blocking

Drug Action by Physical/Chemical Drug Action by Physical/Chemical propertiesproperties

Color – Tincture Card co.Color – Tincture Card co. Physical mass - IspaghulaPhysical mass - Ispaghula Smell - Volatile OilsSmell - Volatile Oils Taste - BittersTaste - Bitters Osmotic action – Mannitol, MagsulfOsmotic action – Mannitol, Magsulf Adsorption - CharcoalAdsorption - Charcoal Soothing-demulcent – Soothing agents like calamine Soothing-demulcent – Soothing agents like calamine Electrical charge – Electrical chargeElectrical charge – Electrical charge Radioactivity - Iodine and othersRadioactivity - Iodine and others Radio-opacity – Barium sulfate Radio-opacity – Barium sulfate Chemical properties – Chelating agents (EDTA, dimercaprol)Chemical properties – Chelating agents (EDTA, dimercaprol)

SummarySummary Basic Principles of PharmacodynamicsBasic Principles of Pharmacodynamics Mechanisms of drug action – Enzymes, Ion channels, Mechanisms of drug action – Enzymes, Ion channels,

Transporters and Receptors with examplesTransporters and Receptors with examples Definitions of affinity, efficacy, agonist and antagonists etc.Definitions of affinity, efficacy, agonist and antagonists etc. Drug transducer mechanismsDrug transducer mechanisms GPCR and different GPCR transducing mechanisms – cAMP, GPCR and different GPCR transducing mechanisms – cAMP,

Protein kinase etc.Protein kinase etc. Up regulation and down regulation of receptors and Up regulation and down regulation of receptors and

desensitizationdesensitization Principles of dose response curves and curves in relation to Principles of dose response curves and curves in relation to

agonist, competitive antagonist etc.agonist, competitive antagonist etc. Therapeutic index, margin of safety and risk-benefit ratio Therapeutic index, margin of safety and risk-benefit ratio

conceptsconcepts Combined effects of drugs – synergism etc. Combined effects of drugs – synergism etc. Concept of spare receptorsConcept of spare receptors

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