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MD3001 Respiratory > Mechanism and Action of Antibiotics > Flashcards

Mechanism and Action of Antibiotics Flashcards

1
Q

What are the main principles of antibiotic use?

A
  • they target processes that humans do not possess (eg. bacterial cell wall)
  • target processes that humans possess but bacterial versions are sufficiently different
  • selective toxicity: antibiotics have greater toxicity to bacteria than human
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2
Q

What are the antibiotics that are active against the cell membrane?

A
  • beta-lactam and cephalosporin
  • glycopeptide
  • cyclic peptide
  • phosphonic acids
  • lipopeptides
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3
Q

What are the targets, mechanisms and examples of beta-lactam and cephalosporin?

A
  • target: penicillin binding proteins
  • mechanism: prevent peptidoglycan cross-linking

Examples:

  • penicillin G
  • flucloxacillin
  • tazobactam
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4
Q

What are the targets, mechanisms and examples of glycopeptides?

A
  • target: C-terminal D-Ala-D-Ala
  • mechanism: prevents transglycolation and transpeptidation (blocks addition of new peptidoglycan building blocks)

Examples:

  • vancomycin
  • teicoplanin
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5
Q

What are the targets, mechanisms and examples of cyclic peptides?

A
  • target: C 55-isopropyl pyrophosphate
  • mechanism: prevents carriage of building-blocks of peptidoglycan bacterial cell wall outside of the inner membrane

Examples:

  • bacitracin
  • polymyxin
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6
Q

What are the targets, mechanisms and examples of phosphonic acids?

A
  • target: murA protein
  • mechanism: inhibits first stage of peptidoglycan synthesis
  • example: fosphomycin
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7
Q

What are the targets, mechanisms and examples of lipopeptides?

A
  • target: cell wall stress stimulon
  • mechanism: calcium dependent membrane depolarisation
  • example: daptomycin
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8
Q

What are the 3 main classes of bacterial cell wall inhibitors?

A
  • beta-lactams (penicillins and cephalosporins)
  • vancomycin
  • bacitracin
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9
Q

What effect does inhibiting cell wall synthesis have?

A
  • normally leads to death of bacteria

- imbalance in cell wall architecture triggers bacterial autolysins that kill cell

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10
Q

What are the 3 types of bacteria that penicillins G and V attack (with examples)?

A
  • gram positive and gram negative cocci:
  • staphylococcus (infections of wounds)
  • streptococcus - haemolytic (septic infections)
  • enterococcus (endocarditis)
  • pneumococcus
  • neisseria gonorrhoeae
  • neisseria menigitidis
  • gram positive rods:
  • clostridium (tetanus, gangrene)
  • spirochaetes:
  • treponema (syphilis)
  • actinomyces (abcesses)
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11
Q

What are examples of B-lactamase-resistant penicillans and the spectrum of bacteria is covers?

A
  • methicillin
  • oxacillin
  • naficillin
  • covers same spectrum as penicillins G and V
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12
Q

What are examples of broad-spectrum penicillins and the spectrum of bacteria it covers?

A
  • ampicillin
  • amoxicillin
  • covers same spectrum as penicillins G and V
  • covers B-lactamase-free strains of:
  • H. influenzae
  • N. Gonorrhoeae
  • E. Coli
  • salmonella
  • morasella catarrhalis (sinusitis)
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13
Q

What are examples of extended-spectrum penicillins and the spectrum of bacteria it covers?

A
  • carbenicillin
  • ticaracillin
  • azlocillin
  • piperacillin
  • covers same as broad-spectrum
  • plus pseudomonas aeruginosa
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14
Q

What are carbapenems and their features?

A
  • broader anti-bacterial spectrum than B-lactase
  • generally resistant to typical beta-lactamases
  • bind PBPs permanently acylating them (penicillin binding proteins)
  • poorly active against MRSA
  • not active against bacteria with no cell wall
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15
Q

What is the role of PBPs?

A

involved in final synthesis of bacterial cell wall

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16
Q

What are the 3 mechanisms of bacterial resistance to B-lactam antibiotics with examples?

A
  • bacteria produces B-lactamase which destructs antibiotic (eg. S. aureus)
  • failure to reach target enzyme, gram negative organism changes outer membrane porins and polysaccharide components (eg. pseudomonas)
  • failure to bind to the transpeptidase (eg. S.pneumoniae)
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17
Q

What are the 4 classes of B-lactamases and their mechanisms of action?

A
  • A, B, C and D
  • ACD uses serine to hydrolyse
  • B uses zinc ions to hydrolyse
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18
Q

What is the use of B-lactamase inhibtors?

A

can be used with B-lactam antibiotic as an alternaltive to B-lactamase-resistant antibiotcs

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19
Q

What are cephalosporins with examples, the infections they treat and the possible complication

A
  • alternative to penicillins
  • classified by generations (1st, 2nd, 3rd)

treats:

  • septicaemia
  • pneumonia
  • meningitis
  • biliary tract infections
  • UTIs
  • sinusitis

Examples:

  • cefalexin
  • cefuroxime
  • cefotaxime
  • cefadroxil
  • complication: overuse facilitates emergence of C. difficile
20
Q

Describe how vancomycin works and the problem with resistance

A
  • binds to peptide chain of peptidoglycan
  • interferes with elongation of peptidoglycan backbone
  • very specific interaction with D-Ala-D-Ala (so minimal resistance)
  • resistance in MRSA and some strep/entero-cocci
21
Q

Describe how bacitracin works and what it can be used for

A
  • bactericidal
  • interferes with dephosphorylation of lipid carrier which moves early cell wall components through membrane
  • can be used in ointment to treat skin and eye infections by streptococci/staphylococci
22
Q

What antibiotics are folate antagonists?

A
  • sulphonamides

- trimethoprim

23
Q

Describe how sulphonamides and trimethoprims work

A
  • act through inhibition of folate pathway in bacteria (important in cell metabolism)
  • bacteria must make own supply of folate (but we do not)
  • makes bacteria susceptible to drugs which interfere with folate metabolism (selective toxicity target)
24
Q

What are the clinical uses of sulphonamides and trimethoprim?

A
  • trimethoprim: community UTIs
  • sulphamethoxazole used with pyrimethamine for drug-resistant malaria and toxoplasmosis
  • can both be used in combination as Co-trimoxazole for
  • toxoplasmosis
  • with other drugs for opportunistic infections in AIDS (eg. pneumocystis jiroveci)
25
Q

Describe how chloramphenicol, streptomycin, erythromycin and tetracycline interfere with the bacterial ribosome

A
  • chloramphenicol: binds to 50S r-RNA and inhibits formation of peptide bond
  • streptomycin: changes shape of 30S r-RNA and causes m-RNA to be read incorrectly
  • erythromycin: binds to 50S r-RNA and prevents movement along m-RNA
  • tetracycline: interferes with t-RNA anticodon reading of m-RNA codon
26
Q

What are examples of macrolides and what are they used for?

A
  • erythromycin
  • clarithromycin
  • used as alternative to penicillins in patients who are penicillin sensitive

used for:

  • mycoplasma chlamydia
  • management of LRTI
  • leigonella

can be used for:

  • corynebacterium (diptheria)
  • camphylobacter (diarrhoea)
  • chlamydia trachomatis
  • toxoplasma gondii
27
Q

What are the side effects of erythromycin and clarithromycin?

A
  • erythromycin:
  • mild gut disturbances
  • hypersensitivity reactions
  • transient hearing disturbances
  • rare - cholestatic jaundice
  • clarithromycin: same but with QT prolongation
28
Q

What are the side effects of clindamycin?

A
  • mainly GI disturbances (but potentially fatal)
  • pseudomembraneous colitis (acute inflammation of colon due to necrotising toxin produced by clindamycin-resistant C. diff)
29
Q

What class is clindamycin in and what is it used for?

A
  • lincosamide class
  • active against gram-positive cocci
  • active against aerobic species
  • combination use against anaerobic sepsis and necrotising faciitis, for staph infections of joints and bones
  • used in eye drops for staph conjuntivitis
30
Q

What are aminoglycosides used to treat and why are they only for serious infections?

A
  • enterobacteriaceae and pseudomonas that give rise to septicaemia and serious UTIs
  • hospital acquired pneumonia, respiratory and intra-abdominal infection due to pseudomonas
  • rare problematic infections such as brucellosis
  • only used in serious infections due to relative toxicity and parenteral administration
31
Q

What are the side effects of aminoglycosides?

A
  • renal toxicity
  • ototoxicity with progressive damage to and destruction of sensory cells in cochlea and vestibular organ of the ear
  • results in vertigo, ataxia, loss of balance and auditory disturbances (can cause deafness)
  • neuromuscular block (if given with neuromuscular blocker)
32
Q

What are the cautions for aminoglycosides?

A
  • caution for elderly
  • caution with renal failure
  • interaction with other renal toxic drugs
  • caution in severe sepsis that is causing acute renal failure
33
Q

What are tetracyclines used to toreat?

A
  • rickettsia
  • mycoplasma
  • chlamidya
  • brucellosis
  • cholera
  • plague
  • lyme disease
  • tigecycline used in management of resistant gram negative infection
  • COPD
  • chronic acne
34
Q

What are the side effects of tetra cyclines?

A
  • gut upset
  • hepatic and renal dysfunction
  • photosensitivity
  • binding to bone and teeth causing staining, dental hypoplasia and bone deformities
  • vestibular toxicity (dizziness/nausea)
35
Q

What is chloramphenicol used for and why can it only be used as a last resort?

A
  • broad spectrum
  • meningitis
  • brain abscess
  • only used as last resort due to low risk of aplastic anaemia
36
Q

Describe the action of topoisomerase IV

A
  • tetrameric enzyme of 2 ParC and 2 ParE sub-units
  • involved in chromosomal partitioning
  • catalyses ATP dependent relaxation of negatively and positively supercoiled DNA and unknotting of un-nicked duplex DNA
  • no action against super-coiling
37
Q

Describe the action of DNA gyrase

A
  • tetrameric enzyme of 2 GyrA and 2 GyrB
  • forms transient covalent bond with DNA
  • breaks DNA
  • passes DNA through break
  • repairs break
38
Q

What are fluroquinolones used for?

A
  • against enterobacteriaceae
  • H. influenzae
  • B-lactamase-producing N. gonorrhea
  • camphylobacter (diarrhoea)
  • pseudomonas aeruginosa
  • salmonella
39
Q

What are the quinolone antibiotics?

A
  • naladixic acid
  • norfloxacin
  • ciprofloxacin
  • moxifloxacin
  • gatifloxacin
  • gemifloxacin
40
Q

What is the spectrum and use of naladixic acid?

A
  • spectrum: gram negative bacilli

- use: UTI

41
Q

What is the spectrum and use of nor/ciprofloxacin

A
  • spectrum: gram negative bacilli, mycobacteria, chlamydia

- use: systemic infection

42
Q

What is the spectrum and use of moxi/gati/gemifloxacin?

A
  • gram positive bacteria
  • gram negative bacilli
  • mycobacteria
  • chlamydia

use: UTI, systemic infection and LRTIs

43
Q

What is metronidazole and how does it work?

A
  • antiprotozoal agent

- under anaerobic conditions it generates toxic radicals that damage bacterial DNA

44
Q

What is metronidazole used for?

A
  • anaerobic bacteria like bacteriodes, clostridia, streptococci
  • anaerobic infections such as sepsis secondary to bowel disease
  • pseudomembranous colitis
  • used with other drugs for helicobacter pylori infections that give rise to peptic ulceration
45
Q

What are the inhibitors of bacterial ribosomal actions?

A
  • macrolides eg. erythromycin and clarithromycin
  • clindamycin
  • aminoglycosides
  • tetracyclines
  • chloramphenicol
46
Q

What are the antibiotics which affect topoisomerase II?

A
  • fluoroquinolones
  • quinolone (naladixic acid/norfloxacin/ciprofloxacin)
  • metronidazole

MD3001 Respiratory (38 decks)

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