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Mechanism Of Action Of Anti-Microbial AgentsDr. Waseem A. SiddiquiPGY-3, PharmacologyMIMER Medical College

19-Aug-151

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HistoryAntimicrobial chemotherapy started with clinical use of sulfonamide 1936

Golden age 1941 Because of penicillin

30% of Hospitalized patients- >1 ATB

Among most misused agents in practice

Wide spread use- emerging resistance

19-Aug-152

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AntibioticsSubstances produced by various speciesof microorganisms: bacteria, fungi, actinomycetes- to supress the growth of other microorganisms & to destroy them

Today the term ATB extends to include synthetic antibacterial agents: sulphonamides and quinolones.

19-Aug-153

Definitions Chemotherapy Treatment for diseases caused by bacteria, other microorganisms, parasites, & tumor cells

Objective of chemotherapy is to study & to apply the drugs that have highly selective toxicity to pathogenic microorganisms & have no or less toxicity to host.19-Aug-154

ANTi BACterial19-Aug-155

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Classification on MOAInhibition of cell wall synthesis

Distruption of cell membrane function

Inhibition of protein synthesis

Inhibition of DNA gyrase, RNA polymerase

Inhibiton of folic acid metabolism

19-Aug-156

19-Aug-157

Classification on mechanism of actionInhibition of cell wall synthesis

Penicillins & cephalosporins prevent synthesis of wall by binding to one or more PBPs, which inhibits transpeptidation (cross bridging) of peptidoglycan units

Imperfect cell wall formation

Osmotic drive from Outside Inside

Bacteria swells, Burst & die

19-Aug-158

PBP- penicillin binding protein8

Classification on mechanism of actionInhibition of cell wall synthesisCell wall of bacteria contains 40 layers of peptidoglycans

Each layer consists of multiple A.A sugars N- acetylglucosamine & N- acetylmuramic acid

N- acetylmuramic acid has short peptide side chains that cross- linked to form polymeric lattice(strong layer)

This synthesis of peptidoglycan is vulnerable step & blocked at several points by antibiotics19-Aug-159

19-Aug-1510

Classification on mechanism of actionPenicillin, Cephalosporins & other - lactams Inhibit final transpeptidation by forming covalent bond with PBPs that have transpeptidase & carboxypeptidase activities (prevents crosslinks formation)Also inactivates inhibitor of autolytic enzyme in cell wall

19-Aug-1511

Classification on mechanism of actionCycloserine, a structural analogue of D- alanine, prevents addition of alanine residues to initial tripeptide side chain on N- acetylmuramic acid by competitive inhibitionVancomycin, inhibits release of building block unit from the carrier & prevent its addition to growing end of peptidoglycan

19-Aug-1512

Classification on mechanism of actionB. Inhibition of functions of cellular membranePolymyxins distrupt bacterial cell wall membrane Osmotic integrity

Displace Ca & mg (cationic detergent)

Important materials will outflow from bacterial cells and result in death of bacteria.19-Aug-1513

Classification on mechanism of actionInhibition of protein synthesis

Eucaryotic cells have 80S (60S + 40S subunits) ribosomes.Procaryotic cells have 70S (50S + 30S subunits) ribosomes.

70S ribosome consists of 50S & 30S subunitS50S has three sites A (acceptor) P (Peptidyl) & EIncoming tRNA binds to A site by complementary base-pairingPeptide chain on tRNA in P site is transferred to tRNA on A site (Transpeptidation)Discharged tRNA trasferred from P site to E sitetRNA with growing peptide chain is translocated from A to P siteA- site again free to attach new t-RNA with AA.

19-Aug-1514

Steps in bacterial protein synthesis and targets of (1) chloramphenicol; (2) macrolides,clindamycin, and type B streptogramins; and (3) tetracyclines. The 70S ribosomal mRNAcomplex is shown with its 50S and 30S subunits. The peptidyl tRNA at the donor site donates thegrowing peptide chain to the aminoacyl tRNA at the acceptor site in a reaction catalyzed bypeptidyl transferase. The tRNA, discharged of its peptide, is released from the donor site to makeway for translocation of the newly formed peptidyl tRNA. The acceptor site is then free to beoccupied by the next "charged" aminoacyl tRNA.14

19-Aug-1515

MACROLIDES

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Classification on mechanism of actionMACROLIDES- Bind to 50s sub unit & inhibit translocation from A-site to P- site; hence site get blocked & protein synthesis stops

AMINOGLYCOSIDES- Aminoglycoside diffuse through aqueous channels formed by porin proteins Blocks association of 50S subunit with mRNABinds to 30s ribosomal sub units & prevents the formation of initiation complex. Lack of initiation complex causes 30S sub unit to misread genetic code on mRNA (bacteriocidal)

19-Aug-1516

70S has 50S & 30S, 50S has two sites A (acceptor) P (Peptidyl).Nascent peptide chain is attached to P site.Next AA transported to A site from tRNA having complementry base pair.Peptide bond formed between peptide chain & newly attached AA.Then chain is shifted from A to P,A should be free to attach new AA.16

TETRACYCLINES- Bind to 30S ribosomal subunit & competitively block attachment of aminoacyl t-RNA to A site

CHLORAMPHENICOL: binds reversibly to 50S ribosomal subunitPrevents binding of aminoacyl tRNA to A-site

19-Aug-1517

Classification on mechanism of actionInhibition of nucleic acid synthesisStop DNA replicationQuinolones- Inhibit DNA gyrase (Topoisomerase 2) & Topoisomerase 4

Gyrase introduces negative supercoils into DNA to combat excessive positive supercoiling that can occur during DNA replication

19-Aug-1518

DNA Gyrase inhibits double stranded DNA & introduces negative supercoiling & release the nick end.This prevents excessive supercoiling18

Classification on mechanism of action

19-Aug-1519

Classification on mechanism of actionInhibition of folic acid synthesisSULFONAMIDE, competitive antagonists of PABA, a precursor of folic acid that is essential for the synthesis of purine nucleotides for DNA and RNAEnzyme of cell recognizes the drug instead of the normal metabolite-Pathway stops

TRIMETHOPRIM, PYRIMETHAMINE inhibits dihydrofolic acid reductaseDHF, FA THF

19-Aug-1520

19-Aug-1521

DRUGSMOAQuinolonesInhibit DNA gyrase and prevent recoiling of DNA after replicationPenicillins, Cephalosporins, & other - lactum inhibits the formation of peptidoglycan crosslinks (transpeptidation) in bacterial cell walls AminoglycosidesCause misreading of mRNA by the ribosome, leading to abnormal protein productionMacrolidesBind to 50s sub unit & inhibit translocation from A-site to P- siteTetracycline & ChloramphenicolBind to 30S ribosomal subunit & block attachment of aminoacyl t-RNA to A site Sulphonamides & TrimethoprimSulphonamides-Competitive antagonists of PABATrimethoprim- Inhibits Dihydrofolate reductase (DHF, FA THF)

19-Aug-1522

PENICILLINS- Osmotic drive from outside (Isotonic) to inside (Hypertonic) cytoplasm; activation of autolysis enzyme & final death.AMINOGLYCOSIDES- Binds to 30s ribosomal sub units & prevents the formation of initiation complex. Lack of initiation complex causes 30S sub unit to misread genetic code on mRNAMACROLIDES- Bind to 50s sub unit & inhibit translocation from A-site to P- site; hence site get blocked and protein synthesis stops

Suphoamides are competitive antagonists of paraaminobenzoic acid (PABA), a precursor of folic acid that is essential for the synthesis of purine nucleotides for DNA and RNA

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Anti- Tubercular DrugsDRUGSMOAIsoniazid (INH)Inhibits synthesis of mycolic acid, an essential component of mycobacterial cell wallRifampin (RMO) & RifabutinBinds to subunit of DNA-dependant RNA polymerase & inhibit it(no new RNA synthesis)Ethambutol (ETB)Inhibits arabinosyl transferase enzyme & prevents polymerisation of arabinoglycans (essential component of mycobacterial cell wall)Pyrazinamide (PZA)Activated to pyrazionic acid under acidic condition Inhibits mycobacterial fatty acid synthase-1 enzyme & disrupts mycolic acid synthesisBinds to ribosomal protein S1 & inhibits translation

19-Aug-1523

Pza not active at neutral pH but becomes bacteriostatic at acidic pH23

Anti-leprosy DrugsDRUGSMOADapsoneInhibits folic acid synthesisClofazimineBinds to mycobacterial DNA & inhibit bacterial growth

19-Aug-1524

Anti viral

19-Aug-1525

Stages of viral replication

Cell entry attachment - penetration UncoatingTranscription of viral genomeTranslation Assembly of virion componentsRelease

19-Aug-1526

classificationDNA Polymerase Inhibitors Purine Analogues (Acyclovir, Ganciclovir, Cidofovir) Pyrimidine Analogues (Idoxuridine, Trifluridine) Non- Nucleosides (Foscarnet)

m-RNA Synthesis Inhibitors (Ribavirin, Fomivirsen)

Viral Penetration & Uncoating Inhibitors (Amantadine, Rimantadine)

Neuraminidase Inhibitors (Oseltamivir, Zanamivir)

Immunomodulator (Interferons, Palivizumab)19-Aug-1527

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MOA of Aciclovir & congenersConverted to monophosphate by viral thymidine kinase (activated in infected cells)Host cell converts monophosphate to triphosphate (active form)Active form inhibits viral DNA-polymerase (terminating nucleotide chain)

19-Aug-1528

m-RNA Synthesis Inhibitors (Ribavirin, Fomivirsen)

Host cell enzymes phosphorylate ribavirin to mono, di & tri- phosphate derivativesRibavirin monophosphate competitively inhibits cellular dehydrogenase & interfere with GTP synthesisRibavirin triphosphate inhibits GTP synthesis & influenza virus transcription activityIt also enhance mutagenesis19-Aug-1529

Alter cellular nucleotide pools & inhibit synthesis of viral m-RNA

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Amantadine, Rimantadine

Inhibit viral uncoating by inhibiting the viral membrane protein M2 (Influenza A)

Also effect on late step in viral assembly, mediated through altering hemagglutinin processing

Influenza- B contains different type of protein

19-Aug-1530

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Neuraminidase inhibitors :Influenza contains an enzyme neuraminidase which is essential for the replication of the virus

Neuraminidase cleaves terminal sialic acid residues & destroys receptors recognized by viral hemagglutinin (present on cell surface, progeny virions & respiratory secretions), this action is essential for release of virus from infected cells

Neuraminidase inhibitors causes conformational change within enzymes active site & inhibits its activity

Viral aggregation at cell surface & spread

Eg Oseltamivir, Zanamavir

19-Aug-1531

InterferonsInterferons (IFNs) are natural proteins produced by the cells of the immune systems in response to challenges by foreign agents (viruses, bacteria, parasites and tumor cells)

Three classes of interferons , ,

19-Aug-1532

Interferons MOAInduction of the following enzymes:1) a protein kinase which inhibits protein synthesis2) an oligo-adenylate synthase which leads to degradation of viral mRNA3) Phosphodiesterase The action of these enzymes leads to an inhibition of translation

19-Aug-1533

DRUGSMOAAciclovir & congenersInhibit viral DNA-polymerase & gets incorporated into DNA & cause chain terminationm-RNA Synthesis Inhibitors Inhibit synthesis of viral m-RNA & DNA by depleting intracellular nucleotide reservesAmantadine, RimantadineInhibit viral uncoating by inhibiting the viral membrane protein M2Neuraminidase inhibitors Influenza contains an enzyme neuraminidase, which is essential for the replication of the virusNeuraminidase inhibitors prevent the release of new virions and their spread from cell to cell

19-Aug-1534

InterferonsInduction of the following enzymes:1) Protein kinase which inhibits protein synthesis2) an oligo-adenylate synthase which leads to degradation of viral mRNA3) a phosphodiesterase which inhibit t-RNA The action of these enzymes leads to an inhibition of translation

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Anti-retroviral

19-Aug-1535

Anti- retroviralNRTIs Nucleoside reverse transcriptase inhibitors [Zidovudine (AZT), Stavudine (d4T), Lamivudine (3TC), Didanosine (ddI), Abacavir (ABC)]Nucleotide reverse transcriptase inhibitors (NtRTI) (Tenofovir)NNRTIs non-nucleoside reverse transcriptase inhibitors [Nevirapine (NVP), Efavirenz (EFV)]

PIs protease inhibitors [Lopinavir, Ritonavir, Nelfinavir , Saquinavir-HGC, Indinavir, Fosamprenavir]

Fusion Inhibitors (Enfuvirtide)

19-Aug-1536

19-Aug-1537CXCR4

19-Aug-1538DRUGSMOANucleoside reverse transcriptase inhibitors (NRTI)NRTIs compete with the normal physiological nucleosides used for DNA synthesis.Act as "false building blocks,Nucleoside analogs incorporate themselves, preventing DNA synthesisNucleotide reverse transcriptase inhibitors (NtRTI)Hook on reverse transcriptase & stop it from workingDNA copy of viral RNA cannot be made & life cycle breaks downPIs protease inhibitors Protease is essential for conversion of inert polyprotein into structural & functional protein by cleavage at appropriate positionHIV specific PI bind to site where cleavage occursFusion Inhibitors Binds to gp41 & gp120 & prevents HIV entry into host cell

Nucleoside reverse transcriptase inhibitors

[Zidovudine (AZT), Stavudine (d4T), Lamivudine (3TC), Didanosine (ddI), Abacavir (ABC)]

19-Aug-1539

NRTIs compete with the normal physiological nucleosides used for DNA synthesis. They differ from the normal substrates only by a minor modification in the sugar (ribose) molecule. Acting as "false building blocks, nucleoside analogs incorporate themselves, preventing DNA synthesisThus they prevent the development of functional viral DNA39

PIs protease inhibit

19-Aug-1540

Protease is essential for conversion of inert polyprotein into structural & functional protein by cleavage at appropriate positionHIV specific protease inhibitor bind to site where cleavage occurs.

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Fusion InhibitorsBinds to gp41 & gp 120 and prevents HIV entry into host cell

19-Aug-1541

Anti malarial19-Aug-1542

Life cycle of Plasmodium* 19-Aug-1543

ChloroquineIt is unchanged at neutral pH & can diffuse into parasite lysosomeAt acidic pH of lysosome, it is converted to a protonated, membrane impermeable form & trapped inside the parasiteBinds to & inhibits haem polymerase, [polymemerises toxic free haem to haemozin]Toxic free haem is poisonous to parasite & interferes with Hb utilization by parasites

19-Aug-1544

Haem polymerase, [polymemerises toxic free haem to haemozin]

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Quinine & MefloquineMECHANISM OF ACTION: It is weak baseInhibits polymerisation of haeme to hemozinFree haeme or haeme- quinine complex damages parasite membrane & kill it

19-Aug-1545

ANTIFOLATESPyrimethamine, ProguanilIt is an inhibitor of DHFRase & has poor action on bacterial DHFRase

19-Aug-1546

Pyrimrthamine directly inhibits DHFRaseProguanil cyclized into the body to triazine derivative, which inhibits DHFRase46

ARTEMISININ DERIVATIVESArtemisinins act by binding iron, breaking down peroxide bridges leading to generate of free radicals Free radicals damage parasite proteins, causes lipid peroxidation, damages ER, & lysis of parasite

19-Aug-1547

Free radicals inhibits plasmodial sarcoplasmic endoplasmic ca ATPase labelled Pf ATP647

DRUGSMOAChloroquineBinds to & inhibits DNA and RNA polymerase; interferes with metabolism & Hb utilization; inhibits prostaglandin effectsQuinine,Mefloquine oxygen uptake & carbohydrate metabolism; intercalates into DNA, disrupting the parasite's replication & transcriptionPrimaquineActs by forming redox compounds that act as cellular antioxidantAntifolateAct synergistically to target enzymes involved in folate synthesisArtemisinin derivativesAct by binding with iron, breaking down peroxide bridges leading to the generation of free radicals that damage parasite proteins.

19-Aug-1548

Chloroquine- Prevent polymerisation of heme to hemozen, heme is toxic to parasite48

Anti fungal

19-Aug-1549

Classification on MOAEchinocandins: e.g. Caspofungin, Micafungin, AnidulafunginPolyene group: e.g. Amphotericin- B, NystatinAllylamine: e.g. TerbinafineAzoles: e.g. Ketoconazole, Fluconazole, Traconazole, VoriconazoleInhibition of nucleic acid synthesis: e.g. 5- FlucytosineInhibition of fungal mitosis: e.g. Griseofulvin

19-Aug-1550

19-Aug-1551Lanosterol 14- demethylaseSqualene epoxidase

EchinocandinsThey inhibit enzyme - glucan synthase

Fungal cell wall lysis due to lack of 1,3-- glucan (an essential component of fungal cell wall)

Mammalian cell wall does not required 1,3-- glucan

Selective toxicity to fungi19-Aug-1552

Amphotericin- B (Polyene)

19-Aug-1553

It acts on fungal cell membrane & interferes with permeability by forming large pores in membraneIts hydrophilic core creates ion channel, causing distrubance in ion by excessive K lossSelectivity to fungi & protozoa coz ergosterol is exclusively present in fungiPrincipal sterol in mammalian cell membrane in cholesterol, Am-B has very less affinity for cholesterol53

Terbinafine & Azole GroupTerbinafine Inhibits enzyme squalene epoxidase

Azole group bind to cyt p-450 dependent 14-- demethylase enzyme (demethylation of lanosterolergosterol)

19-Aug-1554

Flucytosine (5- Fluororcytosine; 5-FC)Transported into fungal cells by enzyme cytosine deaminase, where it gets converted into 5-Fluorouracil (5-FU)5-FU metabolised to 5- Fluorodeoxyuridine monophosphate (5-FUMP)5- FUMP is a competitive inhibitor of thymidylate synthetase, blocks the formation of thymidine monophosphate (inhibit DNA Synthesis)

19-Aug-1555

GriseofulvinIt binds to microtubule of fungi & prevents spindle formation & mitosis in fungiIt also binds to keratin & protect newly formed skin

19-Aug-1556

DRUGSMOAEchinocandinsCauses fungal cell wall lysis by inhibiting synthesis of 1,3-- glucan Amphotericin- B (Polyene)Binds to ergosterol & inhibits cell wall sythesisTerbinafineInhibits squalene epoxidase enzymeAzole GroupInhibits14-- demethylase enzyme Flucytosine (5- Fluororcytosine; 5-FC)Inhibits DNA SynthesisGriseofulvinBinds to microtubule, prevent spindle formation & mitosis in fungi

19-Aug-1557

Antihelmintics19-Aug-1558

Antihelmintics MOAMay act by causing :

Paralyzing of parasite

Damaging worm leading to elimination by immune mechanisms

Interfere with metabolism of the worm 19-Aug-1559

Antihelmintics MOABENZIMIDAZOLEs (Albendazole, Mebendazole, Thiabendazole, Triclabendazole)

Inhibits microtubule synthesis by binding tubulin

Inhibit mitochondrial reductase causing reduced glucose transport

Intestinal parasites are immobilized & die slowly

19-Aug-1560

Antihelmintics MOAPYRANTEL PAMOATE

Depolarizing NM blocking agents

Open non selective cation channels & induce persistent activation of nicotinic Ach receptor & spastic paralysis of worm

Also inhibits cholinesterases19-Aug-1561

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Antihelmintics MOAPIPERAZINE

Reversibly inhibits neuromuscular transmission in worm, by mimicking GABA, at GABA- gated Cl channels in nematode musle

Paralyzed worms expelled alive by peristalsis

Administered with laxatives to facilitate expulsion19-Aug-1562

Antihelmintics MOANICLOSAMIDE

Worm rapidly killed by inhibition of oxidative phosphorylation19-Aug-1563

Antihelmintics MOADIETHYL CARBAMAZINE

Immobilizes microfilariae

Alters their surface structure ,displacing them from tissues & making them susceptible to destruction by host defense19-Aug-1564

Antihelmintics MOAIVERMECTIN Immobilizes parasites by tonic paralysis of musculature by activating glutamate-gated Cl channels (found only in invertebrates)

19-Aug-1565

DRUGSMOABENZIMIDAZOLES (Albendazole, Mebendazole, Thiabendazole, Triclabendazole)Inhibit microtubule synthesis by binding tubulin.Inhibit mitochondrial reductase causing reduced glucose transportIntestinal parasites are immobilized & die slowlyPYRANTEL PAMOATE Depolarizing NM blocking agents. They open non selective cation channels & induce persistent activation of nicotinic Ach receptorAlso inhibitscholinesterasesPIPERAZINE Reversibly inhibits neuromuscular transmission in worm, by mimicking GABA, at GABA- gated Cl channels in nematode musle.Paralyzed worms expelled alive by peristalsisAdministered with laxatives to facilitate expulsionIVERMECTINImmobilizes parasites by tonic paralysis of musculature by activating glutamate-gated Cl channelsNICLOSAMIDE Inhibitss oxidative phosphorylationDIETHYLCARBAMAZINE Immobilizes parasites & alters their surface structure ,displacing them from tissues & making them susceptible to destruction by host defense mechanism

19-Aug-1566

glutamate-gated Cl channels found only in invertibrates66

THANK YOU19-Aug-1567