Mechanism of Action

Question 1

Penicillins

Answer 1

Interacts with cytoplasmic binding proteins (PBPs) to inhibit transpeptidation reactions involved in cross-linking (the final steps in cell wall synthesis)

Question 2

Cephalosporins

Answer 2

Interacts with cytoplasmic binding proteins (PBPs) to inhibit transpeptidation reactions involved in cross-linking (the final steps in cell wall synthesis)

Question 3

Carbapenems

Answer 3

Interacts with cytoplasmic binding proteins (PBPs) to inhibit transpeptidation reactions involved in cross-linking (the final steps in cell wall synthesis)

Question 4

Monobactams

Answer 4

Interacts with cytoplasmic binding proteins (PBPs) to inhibit transpeptidation reactions involved in cross-linking (the final steps in cell wall synthesis)

Question 5

Vancomycin

Answer 5

Binds at D-ala D-ala muramyl pentapeptide to sterically hinder transglycosylation reactions involved in elongation of peptidoglycan chains (and indirectly preventing transpeptidation)

Question 6

Daptomycin

Answer 6

Inserts itself and aggregates in cell membrane causing change in membrane shape which creates holes that leak ions leading to rapid depolarization and loss of membrane potential which leads to inhibition of protein, DNA, and RNA synthesis

Question 7

Telavancin

Answer 7

Binds at D-ala D-ala muramyl pentapeptide to sterically hinder transglycosylation reactions involved in elongation of peptidoglycan chains (and indirectly preventing transpeptidation)

Question 8

Fosfomycin

Answer 8

Phosphoenolpyruvate (PEP) analog that inhibits MurA enzyme which leads to inhibition of linking the glycan and peptide portions of peptidoglycan

Question 9

Polymyxins

Answer 9

Binds to the lipopolysaccharide (LPS) in outer membrane of gram -ve bacteria and disrupts both outer and inner membranes (detergent-like action)

Question 10

Tetracyclines

Answer 10

Enter organisms via passive diffusion and energy-dependent transport protein unique to bacterial inner membrane and concentrate intracellularly. Bind reversibly to 30S subunit of ribosome preventing binding tRNA to mRNA-ribosome complex, thereby inhibiting bacterial protein synthesis

Question 11

Glycylcyclines

Answer 11

Bind reversibly to 30S subunit of ribosome preventing binding tRNA to mRNA-ribosome complex, thereby inhibiting bacterial protein

Question 12

Aminoglycosides

Answer 12

Enter organisms through porin channels and oxygen-dependent system (anaerobes intrinsically resistant). Bind 30S ribosomal subunit and interfere with assembly of functional ribosomal apparatus and/or cause the 30S subunit of the completed ribosome to misread the genetic code, thereby inhibition bacterial protein synthesis

Question 13

Macrolides and Ketolides

Answer 13

Bind irreversibly to a site on 50S subunit of bacterial ribosome, thus inhibiting translocation steps of protein synthesis. Also they may interfere with other steps such as transpeptidation.

Question 14

Fidaxomicin

Answer 14

Acts on sigma subunit of RNA polymerase, thereby disrupting bacterial transcription, terminating protein synthesis.

Question 15

Chloramphenicol

Answer 15

Binds reversibly to bacterial 50S ribosomal subunit and inhibits protein synthesis at the peptidyl transferase reaction.

Question 16

Clindamycin

Answer 16

Bind irreversibly to a site on 50S subunit of bacterial ribosome, thus inhibiting translocation steps of protein synthesis. Also they may interfere with other steps such as transpeptidation.

Question 17

Quinupristin/Dalfopristin

Answer 17

Each component binds to a separate site on 50S bacterial ribosome. Dalfopristin disrupts elongation by interfering with addition of new amino acids to the peptide chain. Quinupristin prevents elongation similar to Macrolides and causes release of incomplete peptide chain.

Question 18

Linezolid

Answer 18

Binds to the bacterial 23S rRNA of the 50S subunit, thereby inhibiting the formation of the 70S initiation complex.

Question 19

Fluoroquinolones

Answer 19

Enter bacteria through porin channels and inhibit DNA gyrase (bacterial topoisomerase II) and bacterial topoisomerase IV. DNA gyrase inhibition will result in relaxation of supercoiled DNA, promoting DNA strand breakage. Topoisomerase IV inhibition impacts chromosomal stabilization during cell division, thus interfering with separation of newly replicated DNA.

Question 20

Sulfonamides

Answer 20

Synthetic analogs of p-aminobenzoic acid (PABA) that will inhibit bacterial dihydrofolic acid synthesis by inhibiting dihydropteroate synthase

Question 21

Trimethoprim and pyrimethamine

Answer 21

Inhibition of dihydrofolate reductase which lead to decrease availability of tetrahydrofolate which is a cofactor required for purine, pyramidine, and amino acid synthesis

Question 22

Methenamine

Answer 22

A urinary tract antiseptic that decomposes at an acidic pH of 5.5 or less in the urine, thus producing formaldehyde, which acts locally and is toxic to most bacteria

Question 23

Nitrofurantoin

Answer 23

Sensitive bacteria reduce the drug to a highly active intermediate that inhibits various enzymes and damages bacterial DNA

Question 24

Isoniazid

Answer 24

Prodrug that is activated by mycobacterial catalase-peroxidase (KatG). It targets acyl carrier protein reductase (InhA) and beta-ketoacyl-ACP synthase (KasA), which are essential for mycolic acid synthesis

Question 25

Rifamycins

Answer 25

Blocks RNA transcription by interacting with the beta subunit of mycobacterial DNA-dependent RNA polymerase

Question 26

Pyrazinamide

Answer 26

Unclear

Question 27

Ethambutol

Answer 27

Inhibits arabinosyl transferase (an important enzyme in the synthesis of mycobacterial cell wall)

Question 28

Para-aminosalicylic acid (4-Aminosalicylic acid)

Answer 28

Prodrug that converted by dihydropteroate synthase and dihydrofolare synthase to hydroxyl dihydrofolate which is an anti-metabolite that inhibits dihydrofolate reductase

Question 29

Capreomycin and Viomycin

Answer 29

Inhibition of protein synthesis by binding to the 70S ribosome. Also they bind to components in mycobacterial cell wall which result in production of abnormal proteins (that are fatal to the bacteria)

Question 30

Cycloserine

Answer 30

Inhibits cell wall synthesis by inhibiting alanine racemase (converting L-alanine to D-alanine) and D-alanine:D-alanine ligase which are important in peptidoglycan synthesis

Question 31

Ethionamide

Answer 31

A structural analog of Isoniazid that inhibits acyl carrier protein reductase (InhA) which is an essential enzyme in mycolic acid synthesis

Question 32

Dapsone

Answer 32

Inhibits dihydropteroate synthase in the folate syntheis pathway

Question 33

Clofazimine

Answer 33

Inhibits bacterial proliferation by binding guanine bases on bacterial DNA, blocking template function of DNA. Also increase the activity of bacterial phospholipase A2, leading to release and accumulation of toxic lysophospholipids.

Question 34

Bedaquiline

Answer 34

ATP synthase inhibitor (proton pump)

Question 35

Polyenes

Answer 35

Bind ergosterol in plasma membrane of sensitive fungal cells forming pores that disrupt membrane function resulting in cell death

Question 36

Flucytosine

Answer 36

Pyrimidine antimetabolite, bioactivated to 5F-dUMP which binds folic acid & this complex will inhibit thymidylate synthase

Question 37

Azoles

Answer 37

Disrupt membrane structure and function by inhibition of ergosterol biosynthesis through inhibition of C-14 alpha-demethylase (a CYP450 enzyme that demethylate lanosterol to ergosterol)

Question 38

Echinocandins

Answer 38

Interfere with the synthesis of fungal wall by inhibiting the synthesis of beta(1,3)-D-glucan, leading to lysis and cell death

Question 39

Squalene epoxidase Inhibitors

Answer 39

Inhibit squalene epoxidase, thereby blocking the biosynthesis of ergosterol which is the essential component of fungal cell membrane

Question 40

Griseofulvin

Answer 40

Causes disruption of the mitotic spindle and inhibition of fungal mitosis

Question 41

Ciclopirox

Answer 41

Inhibits transport of essential elements in the fungal cell, disrupting the synthesis of DNA, RNA, and proteins

Question 42

Nitroimidazoles

Answer 42

The nitro group serves as an electron acceptor, forming reduced cytotoxic compounds that bind protein and DNA, resulting in protozoal death (in Helminthes they inhibit the assembly of microtubules and irreversibly blocking glucose uptake)

Question 43

Aminoquinolines

Answer 43

Prevent heme biocrystallization, leading to heme build-up. Also associate with heme forming aminoquinolines-heme complex, both of these molecules are highly toxic and will lead to parasite autodigestion

Question 44

Dehydroemetine

Answer 44

Unknown

Question 45

Artemisinin

Answer 45

Unknown

Question 46

Pentamidine

Answer 46

Unknown

Question 47

Suramin

Answer 47

Unknown

Question 48

Melarsoprol

Answer 48

It will be metabolized to Melarsen oxide which is an arsen-oxide that will bind irreversibly to sulfhydryl groups causing inactivation of many enzymes

Question 49

Eflornithine

Answer 49

Irreversible inhibitor of ornithine decarboxylase, thereby inhibit the production of polyamines leading to cessation of cell division

Question 50

Nifurtimox

Answer 50

Undergoes reduction and eventually generates intracellular oxygen radicals which are highly toxic

Question 51

Sodium stibogluconate

Answer 51

Unknown

Question 52

Miltefosine

Answer 52

Unknown

Question 53

Atovaquone-proguanil

Answer 53

Atovaquone inhibits mitochondrial processes like electron transport as well as ATP and pyrimidine biosynthesis. Proguanil inhibits dihydrofolate reductase, thereby preventing DNA synthesis

Question 54

Pyrantel Pamoate

Answer 54

It acts as a depolarizing, neuromuscular blocking agent, causing release of Ach and inhibit Ach esterase, leading to paralysis of the worm which will release its hold on the intestinal tract and expelled

Question 55

Ivermectin

Answer 55

Targets the glutamate-gated chloride channel receptors, enhancing chloride influx causing hyperpolarization which results in paralysis and death of the worm

Question 56

Diethylcarbamazine

Answer 56

Inhibits arachidonic acid metabolism in filarial microfilaria making them more susceptible to innate immunity attack

Question 57

Praziquantel

Answer 57

Increasing membrane permeability to calcium ion resulting in spastic paralysis of worms

Question 58

Niclosamide

Answer 58

It inhibits mitochondrial phosphorylation of ADP which lead to death of worm but not ova

Question 59

Neuroaminidase Inhibitors

Answer 59

Inhibit neuroaminidase, thereby preventing release of new virions and their spread from cell to cell

Question 60

Adamantane antivirals

Answer 60

Interfere with the function of viral M2 protein, possibly blocking uncoating of the virus particle and preventing viral release within infected cells

Question 61

Nucleotide analogs

Answer 61

Act either by inhibiting respective nucleotide formation, thereby blocking RNA or DNA polymerases. Or by being incorporated into viral DNA which leads to termination of chain elongation, thereby preventing replication

Question 62

Protease Inhibitors

Answer 62

Reversible inhibitors of proteases (such as HIV aspartyl protease [Retropepsin]), thereby inhibiting the formation of important enzymes and structural proteins, which prevent maturation of viral particles and results in production of noninfectious virions

Question 63

Nucleoside or Nucleotide Reverse Transcriptase Inhibitors (NTRIs)

Answer 63

They are phosphorylated by cellular enzymes to corresponding triphosphate analogs, which are preferentially incorporated into viral DNA by RT. and because the 3'-hydroxyl group is not present, a 3',5'-phosphodiester bond between an incoming nucleoside triphosphate and the growing DNA chain cannot be formed, and DNA chain elongation is terminated (Host mitochondrial DNA polymerase gamma is susceptible at therapeutic concentrations)

Question 64

Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

Answer 64

Highly selective, non-competitive inhibitors of HIV-1 RT. They bind to RT at an allosteric hydrophobic site adjacent to the active site, inducing conformational change that results in enzyme inhibition (they do not require activation by cellular enzymes)

Question 65

Entry Inhibitors

Answer 65

act either by preventing conformational changes in viral transmembrane glycoprotein gp41 required for entry (Enfuvirtide) or by blocking CCR5 coreceptor (Maraviroc)

Question 66

Integrase Inhibitors

Answer 66

They occupy the active sites in host DNA that integrase acts on, thereby halting the integration process

Question 67

Interferons

Answer 67

Incompletely understood