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Pharmacology > Antibiotics (L21) > Flashcards

Antibiotics (L21) Flashcards

1
Q

what are the 3 antibiotic modes of action?

A

bactericidal

bacteriostatic

bacteriolytic

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2
Q

bactericidal

A

drop in the total number of viable cells, but not all cells are killed off

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3
Q

bacteriostatic

A

both viable and total cells remain constant

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4
Q

bacteriolytic

A

kills bacterial cells but allows them to be recognised by the immune system, causes total cells to drop aswell

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5
Q

common bacterial targets

A
  • cell membrane
  • cell wall
  • protein synthesis
  • RNA polymerase
  • DNA synthesis
  • folate metabolism
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6
Q

structure of penicillins

A

beta lactam ring is the central structure of penicillins

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7
Q

what is a lactam?

A

a cyclic amide - allows interaction with enzymes on the bacterial cell wall

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8
Q

what is a beta lactam?

A

a lactic with a heteroaromatic ring structure, consisting of 3 C atoms and 1 N

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9
Q

what are the types on penicillin?

A
  • benzylpenicllin - original form
  • broad-spectrum penicillin - more effective against gram -ive bacteria (e.g. amoxicillin)
  • beta-lactamase-resistant forms - important against beta-lactamase producing bacteria
  • extended spectrum penicillin
  • reversed-spectrum penicillin - greater activity against gram -ive than gram +ive
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10
Q

benzylpenicillin

A

early penicillin
• breaks down when it hits acidic contents of stomach
• not very well absorbed - orally
• slow IV
• narrow spectrum of activity - gram +ives but only a few gram -ives

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11
Q

broad-spectrum penicillin

A

stuck a different functional group of the side of the beta lactam ring

amino group facilitates penetration of outer membrane of gram -ive bacteria

much better absorption

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12
Q

penicillin mechanisms of action

A

targets the cell wall
• inhibits transpeptidase
• causes bacteria to swell and rupture
• more effective against gram +ive bacteria

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13
Q

what does transpeptidase do?

A

enzyme responsible for the reaction which establishes cross links in the peptidoglycan cell wall

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14
Q

why is penicillin more effective against gram +ive than -ive bacteria?

A

gram +ive have a lot more peptidoglycan strands

gram -ive have a lot more beta lactamase in their cell envelope

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15
Q

what does beta lactamase do?

A

breaks open the beta lactam ring

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16
Q

structure of bacterial cell walls

A

strength and organisation of cell dependent on complex polymer - peptidoglycan strain chains cross-linked together

heteropolymeric - made of repeating units

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17
Q

where do penicillins target the peptidoglycan chains?

A

the side chain connection

on the 4th peptide of the side chain

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18
Q

penicillin absorption

A

vary when given orally

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19
Q

penicillin distribution

A

widely distributed throughout the body but concs in tissues and body fluids varies

don’t normally enter CSF - except with meninges inflammation

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20
Q

penicillin metabolism

A

short half-lives - 30-80 minutes

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21
Q

penicillin excretion

A

mainly though the kidney - 90% excreted by tubular secretion

clearance reduced in neonates

reduce excretion rate by use of probenecid - inhibits tubular secretion

22
Q

adverse reactions to penicillins

A

hypersensitivity
• skin rashes, fever, anaphylactic shock, serum sickness

GIT disturbance
• altered gut flora

haemostatic effects
• blood clotting

23
Q

what do sulphonamides do?

A

inhibit folate biosynthesis

24
Q

how does sulphonamide work?

A

looks structurally similar to pABA

inhibits dihydropteroate synthetase

no DNA production

25
Q

why is sulphonamide selective?

A

humans take in folate from the diet - brought inside the cell

bacterial cells have to make their own

26
Q

sulphonamide absorption

A

80-100% of drug given orally is absorbed from the stomach and intestines

27
Q

sulphonamide distribution

A

widely distributed including CNS

28
Q

sulphonamide metabolism

A

metabolism occurs in the liver by N-acetylation

29
Q

sulphonamide excretion

A

in urine

30 minutes

30
Q

adverse reactions to sulphonamides

A

photosensitivity

stevens-johnson syndrome

haemopoeitic disturbances

31
Q

what are fluoroquinolones?

A

broad spectrum antibiotics

discovered in search for antimalarial drugs

32
Q

mechanism of action of fluoroquinolones

A

target DNA replication via type II topoisomerases

33
Q

type II topoisomerases

A 
DNA gyrase
• regulates super-coiling 
• facilitates movement of transcription and replication complexes though DNA helix 
• removes knots 
• helps fold DNA

DNA topoisomerase IV
• homologue of gyrase
• unlinks daughter DNA replicons

34
Q

what do fluoroquinolones typically inhibit?

A

DNA gyrate in gram -ive bacteria

topoisoemrases in gram +ive bacteria

35
Q

fluoroquinolones absorption

A

oral route most effective

36
Q

fluoroquinolones distribution

A

very well absorbed in upper GI tract

37
Q

fluoroquinolones metabolism

A

potent inhibitor of CYP1A2

38
Q

fluoroquinolones excretion

A

mainly excreted in tubular secretion

39
Q

adverse reactions to fluoroquinolones

A

hypersensitivity

GIT disturbance

40
Q

macrolides mechanism of action

A

target bacterial ribosomes and protein synthesis

block translocation of the newly forming peptide
• binds to site near RNA exit tunnel
• causes peptidyl-transferase RNA drop off

41
Q

macrolides absorption

A

oral route requires protected tablets to avoid inactivation by gastric juices

42
Q

macrolides distribution

A

diffuses readily into most tissues but doesn’t cross BBB

crosses placenta

43
Q

macrolides metabolism

A

metabolised by demethylation (CYP3A4)

can therefore potentiate effects of other drugs

44
Q

macrolides excretion

A

excreted in bile

45
Q

adverse reactions to macrolides

A

cholestatic hepatitis may occur after prolonged use of erythromycin estolate

GIT disturbances seen at large doses

transitory auditory impairment

hypersensitvity reactions

46
Q

tetracyclines mechanism of action

A

target bacterial ribosomes and protein synthesis

interrupts elongation phase of synthesis
• inhibits tRNA binding

47
Q

tetracyclines absorption

A

absorption faster in fasting state and inhibited by concurrent ingestion of dairy products, metal ions and certain antacids

48
Q

tetracyclines distribution

A

widely distributed entering most tissues

49
Q

tetracyclines metabolism

A

relatively long half-lives

6-18 hours due to EHR

50
Q

tetracyclines excretion

A

excreted by bile and the kidneys via glomerular filtration

Pharmacology (24 decks)

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