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Management of Infection > Lecture 7 - Chemistry of Antimicrobial agents > Flashcards

Lecture 7 - Chemistry of Antimicrobial agents Flashcards

1
Q

Antibacterial drugs are able to?

A

kill or inhibit the growth of microbes at low concentrations

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2
Q

How do antibacterial drugs work?

A

selectively

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3
Q

What drugs target cell wall synthesis?

A 
Beta lactams 
glycopeptides
cycloserine 
bacitracin 
fosfomycin
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4
Q

What drugs target DNA gyrase?

A

quinolones

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5
Q

What drugs target RNA polymerase?

A

rifamycins

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6
Q

What drugs are 50S inhibitod?

A

macrolides

chloramphenicol

clindamycin

linezolid

streptogramins

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7
Q

What drug are 30S inhibitors?

A

tetracyclines

aminoglycosides

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8
Q

What drugs target tRNA?

A

mupirocin

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9
Q

What drugs target cytoplasmic membrane structure?

A

polymyxins

daptomycin

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10
Q

What drugs target folic acid metabolism?

A

trimethoprim

sulfonamides

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11
Q

What do porins in gram negative cell walls allow?

A

a way for small antibiotics of low MWt to enter inside the gram negative and target the peptidoglycan

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12
Q

What causes cross linking of the peptide chains in the cell wall?

A

penicillin binding proteins (PBPs)

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13
Q

What does the cross linking achieve?

A

a more rigid structure

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14
Q

What is there at the end of the peptic chain?

A

2 molecules of alanine

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15
Q

What is the peptidoglycan composed of?

A

N-acetylglucosamine (NAG)
N-acetylmuramic acis (NAM)
D-alanine (D-Ala)

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16
Q

What are the 4 classes of the beta lactam antibiotics?

A

penicillin

cephalosporin

carbapenem

monobactam

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17
Q

What structure do the beta lactams contain?

A

4 membered cyclic amide

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18
Q

What is a natural substrate for the penicillin binding proteins?

A

alanine

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19
Q

What is the mode of action of beta lactams?

A

PBP bind to the beta lactams, at forms a complex

this means the enzyme is no longer available to form the peptidoglycan as normal and the synthesis is inhibited

the bacterial wall no longer has a rigid structure and will be killed

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20
Q

What does beta lactam-PBP complexation lead to?

A

irreversible inhibition of cross linking and bacterial cell lysis

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21
Q

What are beta lactams?

A

bactericidal

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22
Q

Why is a primary amide stable?

A

the electrons from the lone pair ca delocalise and move towards the O of the carbonyl, resulting in mesmeric form which always has a double bond tendency

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23
Q

Why is penicillin not very stable?

A

the structure is not planar and the cyclic amide is very constrained and wants to break open

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24
Q

Why are beta lactams very reactive?

A

the electrons of the lone pair cannot delocalise properly because there is no planarity

the bond can quickly open and if it is broken, the beta lactam structure is degraded and there is total loss of antibiotic activity

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25
Q

What does penicillin come from?

A

penicillium mould which is a fungus

discovery made by Alexander Fleming

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26
Q

What are the classes of penicillins?

A

narrow spectrum

broad spectrum

antipseudomonal

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27
Q

What are the divisions of narrow and broad spectrum penicillins?

A

beta lactamase resistant

beta lactamase sensitive

28
Q

What do narrow spectrum penicillins work on?

A

gram positives

29
Q

What do broad spectrum penicillins work on?

A

gram positive and gram negatives

30
Q

What types of penicillins are there?

A

synthetic and natural

oral parenteral

31
Q

What are all natural penicillins?

A

very reactive and degrade very easily in water

facilitated in the presence of protons in acidic medium

32
Q

What can a molecule of water attack?

A

positive delta plus charged carbon of the carbonyl function, leads to a complete opening of the beta lactam ring

33
Q

What does nucleophilic attack in acidic medium do?

A

oxygen attacks the carbonyl and there is degradation, the beta lactam ring is no longer there

34
Q

What does attaching an electronegative group to the left side chain do?

A

minimises neighbouring group attack on the beta lactam carbonyl

pulls the electrons away from the oxygen

35
Q

Narrow spectrum penicillins?

A

benzylpenicillin

phenoxymethyl penicillin

36
Q

Benzylpenicillin?

A

does not contain an electronegative group so is very unstable and cannot be given in acidic medium (orally)

37
Q

Phenoxymethyl penicillin?

A

contains an additional oxygen which is electronegative and is enough to make is less susceptible to degradation

can be given orally

38
Q

What are beta lactamases?

A

proteins which are produced by bacteria in response to being treated with a beta lactam antibiotic

39
Q

What do beta lactamases do?

A

cleave the beta lactam ring, breaking the bat lactam cycle and make the antibiotic totally inactive

40
Q

What is flucloxacillin?

A

resistant to beta lactamases

41
Q

Why is flucloxacillin resistant to beta lactamases?

A

it contains an aromatic cycle (bulky side chain) which will act like a protective shield should a beta lactamase enzyme come near the carbon atom

the presence of the side chain acts like an umbrella to protect the beta lactam from attack

42
Q

If flucloxacillin broad or narrow spectrum?

A

narrow spectrum

works very well on gram positive

43
Q

What is flucloxacillin used for?

A

used as the treatment of choice in staph aureus infections involving skin and soft tissue

44
Q

When is temocillin used?

A

in the presence of beta lactamases

45
Q

Structure of temocillin?

A

in position 6 of the beta lactam ring there is an additional O methyl and this is enough to protect the carbonyl and will act like a hindrance to the beta lactamase enzyme

46
Q

What do beta lactamase inhibitors do?

A

bind covalently to beta lactamases

47
Q

Examples of beta lactamase inhibitors?

A

clavulanic acid and tazobactam

48
Q

Co-amoxiclav?

A

Augmentin = amoxicillin + clavulanic acid

49
Q

Tazocin?

A

Piperacillin + tazobactam

50
Q

What do beta lactamase inhibitors look like?

A

very similar to beta lactams but do not have the side chain on the left

51
Q

What does ampicillin have?

A

additional electronegative group (NH2) so it can be taken orally

52
Q

What does amoxicillin have?

A

Additional electronegative group (NH2) and an additional hydroxyl group

53
Q

Broad spectrum penicillins?

A

Amipicillin and amoxicillin

hydrophilic and have low Mwt so can go through the porins of gram negative

54
Q

Penicillins that work on pseudomonas aeruginosa?

A

ticarcillin and piperacillin

55
Q

How can ticarcillin and piperacillin be given?

A

not orally

they do not have electronegative groups on the side chains

56
Q

Gram positive active cephalosporins?

A

cefalexin, cefradine, cefadroxil, defaclor

57
Q

Beta lactamase resistant cephalosporins?

A

cefuroxime

58
Q

Gram negative active cephalosporins and beta lactamase resistant?

A

cefotaxime, ceftriaxone, cefixime, cefpodoxime

59
Q

Cephalosporins active against pseudomonas aeruginosa and beta lactamase resistant?

A

Ceftazidime

60
Q

Natural cephalosporins?

A

easily degraded

61
Q

Oral (acid stable) cephalosporins?

A

cefalexin and cefaclor

62
Q

Parenteral cephalosporins?

A

ceftazidime

63
Q

What does ceftazidime contain?

A

zwitterion

has both charges at physiological pH

not easily absorbed through membranes as it is not lipophilic

64
Q

Beta lactamase resistant cephalosporins?

A

cefuroxime

contains an extra substituent on the side chain - presence of this is enough to protect the beta lactam and creates a hindrance - means it will not be easily attacked by beta lactamases

cefixime

65
Q

Anti-pseudonmonal cephalosporins?

A

ceftazidime

has the quaternary ammonium making it active on pseudomonas

66
Q

What are the aims of drug development of penicillins?

A

Aim 1 - increase stability in acidic medium

Aim 2 - resistance to beta lactamases

Aim 3 - spectrum of activity

Management of Infection (36 decks)

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