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MD3001resp > the mechanism and action of antibiotics > Flashcards

the mechanism and action of antibiotics Flashcards

1
Q

bet-lactam and cephalosporin:

TARGET?
example?

A

target = penicillin binding proteins

examples= penicillin G, flucloxacillin, Tazobactam

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2
Q

what are the 3 central principles of antibiotics?

A

1) they target processes that humans do not posses

2) they target processes that humans posses but the bacterial versions are sufficiently different

3) the toxicity of antibacterials is greater to bacteria than it is to humans

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3
Q

glycopeptide:

target?
example?

A

target = C-terminal D-Ala-D-Ala

example = vancomycin, teicoplanin

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4
Q

Cyclic Peptide:

target?
example?

A

target = C 55-isopropyl pyrophosphate

example = Bacitracin, Polymyxin

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5
Q

phosphoric acid:

target?
example?

A

target = murA protein

example = fosphomycin

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6
Q

lipopeptides:

target?
example?

A

target = cell wall stress stimulon

example = daptomycin

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7
Q

what are the 3 main classes of cell wall inhibitors?

A

1) B-lactams (penicillins and cephalosporin)
2) Vancomycin
3) bacitracin

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8
Q

describe the action of the bacterial cell wall inhibitors?

A

inhibiting the bacterial cell wall synthesis normally leads to the death of the bacteria
it appears that imbalance in the cell wall architecture triggers bacterial autolysis that kill the cell.

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9
Q

mechanism of action of the glycopeptides?

mechanism of action of peptidoglycan?

A

glycopeptides -inhibit synthesis of peptidoglycan

peptidoglycan cross linking

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10
Q

what 3 things will penicillin be used to treat?

A

Gram positive and gram negative cocci
Gram positive Rods (tetanus)
Spirochaetes (syphillis)

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11
Q

what are the 3 types of penicillin?

A

B-lacatmase resistant penicillin
broad spectrum
extended spectrum

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12
Q

examples of B-lactamase-resitant penicillins?

A

methicillin
oxacillin
nafcillin
cloxacillin
dicloxacilin

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13
Q

what are examples of broad spectrum penicillins?

A

Ampicillin and amoxicillin

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14
Q

examples of extended spectrum antibiotics?

A

Carbenicilin
Ticaracillin
Axlocillin
Piperacillin

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15
Q

describe the structure and function of Carbapenems?

A
  • borad spectrum
  • much broader than other B lactams
  • generally resistant to the typical beta-lactamases
  • carbapenems bing PBPs permentantly acylating them.
  • active againstboth gram positive and gram negative

they will not be active against becateria with no cell wall

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16
Q

what are peptidoglycans?

what are they made from?

what gives it its strength?

A
  • the bacterial cell walls are made of various strands of peptidoglycans which are not present in eukaryotes
  • they are made multiple amino sugars such as NAG and NAMA
  • the cross linking gives it its strength
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17
Q

how do meta lactase function?

what does this lead to?

what is this called?

A
  • they prevent cross linking between side chains of NAMA, meaning that peptide cross-linking can’t occur.
  • this leads to the bacterial cell loosing all its strength and being killed.
  • this is called bactericidal anti-biotic.
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18
Q

What effect does the penicillin nucleus have?

How can we modify it?

what is this called?

A

the penicillin nucleus is not active by itself

  • by adding things to it, we generate antibiotics.
  • this is called semi-synthetic revolution.
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19
Q

what bacteria will penicillin G and v work on?

A
  • staphylococcus
  • streptococcus
  • enterococcus
  • pneumonococcus
  • neisseria gonorrhoea
  • neisseria menigiditis
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20
Q

what are the 4 mechanisms of actions of bacterial resistance to B-lactam antibiotics?

A

1) destruction by B-lactamase

2) failure to reach target enzyme- changes to out membrane porins and polysaccharide components of gram negative organisms

3) failure to bind to the trans peptides

4) inhibition of release of autolysins

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21
Q

what are the 4 classes of B-lactamse inhibitors?

A

A B C D

ACD= uses serine to hydrolyse

B= uses zinc ions to hydrolyse

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22
Q

what compounds are inhibitors of B-lactamse inhibitor for class A?

What is an alternative to B-lactamase resistant antibiotics?

A

the B-lactam compounds CLAVULANIC acid and SULBACTAM act as strong inhibitors of class A but not C and D.

Co-administration of B-lactamase inhibitors with a B-lactam antibiotic is an alternative approach to the use of B-lactamase-resistant antibiotics

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23
Q

What are cephalosporins an alternative to?

How are cephalosporins classified?

A

Cephalosporins are an alternative to penicillins (as they have similar indications).
There are fewer of them and they are classified by generations, 1st, 2nd, and 3rd

24
Q

What 6 conditions can cephalosporins be used to treat?

What are 4 examples of cephalosporins?

What can overuse of cephalosporins result in?

A

1) Septicaemia

2) Pneumonia

3) Meningitis

4) Biliary tract infections

5) Urinary tract infections

6) Sinusitis

4 examples of cephalosporins:
1) Cefalexin

2) Cefuroxime

3) Cefotaxime

4) Cefadroxil

Overuse of cephalosporins can facilitate the emergence of C. difficile

25
Q

What is vancomycin?

What does it bind to?

What does it interfere with?

A
  • Vancomycin is a glycopeptide antibiotic
  • It binds to the peptide chain of peptidoglycan
  • Interferes with the elongation of the peptidoglycan backbone
26
Q

What interaction does vancomycin utilise?

Why is this a positive?

What 3 things that have vancomycin resistance?

A
  • Vancomycin utilises a very specific interaction with D-Ala-D-Ala
  • This is a positive, as it means development of resistance to the antibiotic is very minimal

What 3 things that have vancomycin resistance:
1) MRSA
2) Some resistant streptococci
3) Some resistant Enterococci

27
Q

what is bacitracin?

What does it interfere with?
What can it be used in?

A
  • bacitracin is a polypeptide and is bactericidal
  • it interferes with the dephosphorylation of the lipid carrier which moves the early cell wall components through the membrane
  • it can be used in an ointment to treat infections of the skin ad eye by streptococci and staphylococci
28
Q

what are 2 examples of bacterial folate antagonists?

A

sulphonamides and trimethoprim

29
Q

how do bacterial folate antagonists work and what is the importance of the system that they effect?

A
  • these act through inhibition of the folate pathway in bacteria
  • the folate system is important in cell metabolism
  • bacteria must make their own supply but we don’t as we get it in our diet
  • this makes bacteria susceptible to drugs which interfere with folate metabolism (selective toxicity)
30
Q

what will sulfonamides inhibit?

what will trimethoprim inhibit?

A

sulphonamides = dihydropteroate synthetase

trimethoprim = dihyrofolate reductase

31
Q

what are the 6 therapeutic uses of inhibitors of trimethoprim and sulphonamides?

A

1) trimethoprim is commonly used in UTI treatment

2) they can both be combined to become Co-trimoxazole

3) in combination for the treatment of toxoplasmosis

4) used in combination with other drugs to treat infections if AIDS patients

5) rarely salmonellosis and typhoid due to resistance

6) SMX combined with pyrimethamine used for drug resistance malaria and toxoplasmosis

32
Q

what are 4 different types of antibiotics that act as inhibitors of protein synthesis?

A
  • chloramphenicol
  • erythromycin
  • tetracycline
  • streptomycin
33
Q

what are macrolides?

what are examples?

what do they work against?

A
  • they are used as an alternative to penicillins in patients who are penicillin sensitive.
  • eg - erythromycin and clarithromycin
  • they are active against mycoplasma, chlamydia, legionella, and used in the management of LRTI
34
Q

What do macrolides have a limited spectrum of action against?

What are 4 things macrolides may be used for?

What can macrolides be used in combination with?

A

Macrolides have limited gram-negative spectrum but active against H. Influenzae (dosing is an issue – can lead to toxicity of liver and gallbladder)
4 things macrolides may be used for:
1) Corynebacterium (diphtheria)

2) Campylobacter (diarrhoea)

3) Chlamydia trachomatis

4) Toxoplasma gondii in the context of pregnancy

Macrolides can also be used against Helicobacter pylorii in combination with other agents

35
Q

what are the adverse effects of erythromycin?

what are the adverse effects of clarithomycin?

A
  • mild gut disturbances
  • hypersensitivity reactions
  • transient hearing disturbances and rarely cholestatic jaundice.
  • as above but with QT prolongation
36
Q

what are the adverse effects of clindamycin?

A
  • gastrointestinal disturbances
  • pseudomembranous colitis (acute inflammation of the colon due to a necrotising toxin produced by clindamycin resistant clostridium difficile.
37
Q

what is clindamycin active against?

what is it used in combination with and why?

what is it used in eyedrops to treat?

A
  • it is active against gram-positive cocci including staphylococci
  • active against a wide range of anaerobic species
  • used in combination against anaerobic sepsis and necrotising fasciitis for staphylococcus infections of joints and bones.
  • used in eye drops to treat staphylococcal conjunctivitis.
38
Q

describe the spectrum of activity of aminoglycosides?

A

(the relative toxicity and parenteral administration means that these agents should be reversed for the treatment of serious infections.)

  • enterobacteriaceae and pseudomonas which give rise to UTI
  • hospital acquired pneumonia
  • respiratory and intra-abdominal infections.
39
Q

side effects of aminoglycosides?

A
  • renal toxicity due to damage of the kidney tubules
  • ototoxicity with a progressive damage and destruction of the sensory cells in the cochlea and vestibular organ of the ear.
  • this can result in vertigo, ataxia and loss of balance as well as auditory disturbances including deafness.
  • neuromuscular block (usually only seen when the drug is given with a neuromuscular blocker and it is due to the block of calcium entry into nerves)
40
Q

what are the 4 pharmacokinetic properties of ahminoglycosides?

A
  • polar agent confined to extracellular fluid
  • does not cross the blood brain barrier
  • excreted by the kidney
  • has to be administered intravenously
41
Q

what are 5 cautions in use of ahminoglycosides?

A
  • caution in elderly
  • caution with renal failure
  • interaction with other renal toxic drugs
  • caution in severe sepsis that is causing acute renal failure
  • consider the pharmacokinetics carefully
42
Q

what are tetracyclines the drug of choice for?

what are they used in the management of?

A
  • they are the first drug of choice for rickettsia, mycoplasma and chlamydia infections, brucellosis, cholera, plague and Lyme disease.
  • management of resistant gram negative infection, COPD and treating chronic acne.
43
Q

what are the side effects of tetracyclines?

A
  • gut upset (most common)
  • hepatic and renal dysfunction
  • photosensitivity
  • binding to bone an teeth causing staining, dental hypoplasia and bone deformities
  • vestibular toxicity
44
Q

when would chloramphenicol be used?

A
  • it is a broad spectrum antibiotic
  • low risk of aplastic anaemia means that it now limited to indications for serious infections when no other drug is suitable
  • such indications include meningitis and brain abscesses when other agents cannot be used.
45
Q

What are 3 types of antibiotics which affect topoisomerase?

A

1) Fluroquinolones
2) Quinolones
3) Metronidazole

46
Q

what is topoisomerase IV?

what is it involved in?

what does it catalyse?

what does it have no action against?

A
  • this is a tetrameric enzyme consisting of two ParC and two ParE subunits.
  • involved in chromosomal partitioning
  • catalyses ATP dependant relaxation of negatively and positively supercoiled DNA and unknotting of un-nicked duplex DNA
  • no action against super coil.
47
Q

What is DNA Gyrase?

A

DNA Gyrase is A tetrameric enzyme consisting of two GyrA and two GyrB subunits
It is also a type 2 topoisomerase

48
Q

What are the 4 steps in the mechanism of DNA Gyrase?

How do quinolones affect this mechanism?

A

1) Forms transient covalent bond with DNA

2) Breaks the DNA

3) Passing the DNA through the break

4) Repairs the break

Quinolones dually target DNA gyrase and topoisomerase IV binding to specific domains and conformations (they inhibit bacterial DNA Gyrase)

This blocks DNA strand passage catalysis and stabilizes DNA–enzyme complexes that block the DNA replication apparatus

This generates double breaks in DNA that underlie quinolones’ bactericidal activity.

49
Q

what are the spectrum of activities of fluoroquinolones?

A

Ciprofloxacin - most commonly used

  • good activity against:
    Enterobacteriaceae
    H.infeunza
    B-lactamase producing gonorrhoea
    campylobacter (diarrhoea)
    pseudomonas aurigonosa
    salmonella
50
Q

What is the spectrum and use of:
1) Nalidixic acid
2) Norfloxacin and Ciprofloxacin
3) Moxifloxacin, Gatifloxacin, and Gemifloxacin

A
51
Q

What is metronidazole originally used as?

What does it generate under anaerobic conditions?

A
  • originally used as antiprotozoal agent
  • Under anaerobic conditions, metronidazole generates toxic radicals that damage bacterial DNA
52
Q

What 3 things can metronidazole be used to treat?

When can metronidazole be used with other drugs?

A

1) Active against anaerobic bacteria such as Bacteroides, Clostridia and some streptococci

2) Important in the treatment of anaerobic infections such as sepsis secondary to bowel disease

3) Effective in the therapy of pseudomembranous colitis, a clostridial infection associated with antibiotic therapy

Metronidazole can be used with other drugs (omeprazole, amoxicillin) to treat Helicobacter pylori infections which give rise to peptic ulceration.

53
Q

what are the 2 miscellaneous antibacterial agents?

A

nitrofurans
polymixins

54
Q

nitorfurans:
example?
mechanism of action?

what is it used to treat?

A

nitrofurantoin
- mechanism of action is unknown but it has a broad spectrum of activity against bacteria and development of resistance to it is rare.

used to treat UTI’s due to enterobacteriacaea.

55
Q
A

MD3001resp (41 decks)

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