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S2 Case 2 - Diarrhoea > Antibiotic Chemistry > Flashcards

Antibiotic Chemistry Flashcards

1
Q

What are the different mechanisms of action for antibiotics?

A

Inhibition of bacterial cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid transcription + replication
Injury to plasma membrane
Inhibition of synthesis of metabolites

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2
Q

What is the difference between gram + and gram - bacteria?

A

Gram -:
Very thick and lipophilic membrane
Periplasmic space

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3
Q

Which antibiotics inhibit bacterial cell wall synthesis?

A

Beta lactams

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4
Q

What are beta lactam’s structure?

A

R group
Beta lactam ring = planar
Carboxylic acid

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5
Q

How do beta lactams inhibit bacterial cell wall synthesis?

A

For covalent body
Formation of salt bridge
Blocks H2O + peptide chain

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6
Q

What are the beta lactam adverse reactions?

A

Anaphylaxis
Urticaria
Steven-Johnson syndrome
Acute exanthematic pustulosis

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7
Q

What do beta lactams interact with?

A

Penems + valproic acid
Methotrexate
Warfarin

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8
Q

What is beta lactam resistance?

A

Provides another nucleophilic residue to break up ring + inactivate antibiotic

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9
Q

What does MRSA do?

A

Produces mutated penicillin binding protein
= methicillin doesn’t bind as efficiently

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10
Q

What are some beta lactamase inhibitors?

A

Co-amoxiclav = amoxicillin + clavulanic acid
Tazocin = piperacillin + tazobactam

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11
Q

What do glycopeptides do?

A

Inhibition of bacterial cell wall synthesis

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12
Q

What is an example of glycopeptide?

A

Vancomycin
= used to treat MRSA
Bactericidal

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13
Q

Describe structure of vancomycin

A

Fixed conformation of hexapeptide
Forms H bonding
D-ala-D-ala held in deep cleft

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14
Q

How does vancomycin inhibit bacterial cell wall synthesis?

A

Dimerization can take place
Head to tail
4 H bonds
Steric shield to transglycosidase + transpeptidase enzymes

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15
Q

What is teichoplanin?

A

Glycopeptide
Treat gram +
Bactericidal

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16
Q

What are the adverse reactions to glycopeptides?

A

Anaphylaxis
Hypotension
Red man syndrome

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17
Q

How does vancomycin resistance happen?

A

Modification of cell wall precursors
= D-ala replaced with D-lactic acid
= removes vancomycin H bond = weaker interaction

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18
Q

What does translation require?

A

Ribosomal RNA
Messenger RNA
Transfer RNA

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19
Q

What does chloramphenicol do?

A

Bind to 50S portion + inhibit formation of peptide bond

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20
Q

What does tetracyclines do?

A

Interfere with attachment of tRNA to mRNA-ribosome complex

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21
Q

What does streptomycin do?

A

Change shape of 30S portion = code on mRNA read incorrectly

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22
Q

Which inhibit protein synthesis (translation)?

A

Aminoglycosides = gentamicin
Tetracyclines = doxycycline
Macrolides = clarithromycin
Chloramphenicol
Lincosamides

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23
Q

How do aminoglycosides inhibit protein synthesis?

A

Bind to 16S ribosomal DNA portion of 30S = read ribosome impaired
Conformational change in A site
Mistranslation of RNA template
= incorrect amino acid

24
Q

What happens in aminoglycoside resistance?

A

Due to bacterial elaboration of resistance transfer factor mediated enzymes
= prevents ribosomal binding

25
Q

What can aminoglycosides interact with?

A

Beta lactams
= gentamicin + beta lactam = acylation

26
Q

Are tetracyclines bactericidal or bacteriostatic?

A

Bacteriostatic

27
Q

How do tetracyclines work?

A

Bind to 30S
= aminoacyl-TRNA can’t bind
= stop further addition of amino acids

28
Q

What is an example of tetracycline?

A

Doxycycline

29
Q

What do tetracyclines involve?

A

Mg2+

30
Q

What are the interactions with tetracycline for?

A

Antacids
Ca2+

31
Q

Why do you avoid children having tetracyclines?

A

Form complex with Ca2+
= damage teeth + bones

32
Q

Describe tetracycline epimerisation

A

Orientation of C-4 essential for bioactivity
Reprotonation top = regenerates tetracycline
Reprotonation bottom = inactive
At eqm mixture equal quantity of diastereomers

33
Q

Describe tetracycline dehydration

A

Ideal geometry for acid catalysed dehydration
= biologically in active + deeper colour

34
Q

What does tetracycline dehydration cause?

A

Nephrotoxicity

35
Q

What are the adverse effects of tetracyclines?

A

Teeth staining
Kidney damage
Nausea
Vomiting
Diarrhoea

36
Q

Are macrolides bacteriostatic or bactericidal?

A

Bacteriostatic

37
Q

How do macrolides inhibit protein synthesis?

A

Bind to 23S rRNA polypeptide exit tunnel in 50S ribosomal subunit
= stops polypeptide from exiting

38
Q

What are the drug interactions for macrolides?

A

Metabolised by CYP 3A4 into nitrosoalkanes
= benzodiazepines, statins, neuroleptics

39
Q

Is chloramphenicol bacteriostatic or bactericidal?

A

Bacteriostatic

40
Q

How does chloramphenicol inhibit protein synthesis?

A

Bind to large ribosome subunit 50S
= prevents binding of next charged tRNA

41
Q

Why is chloramphenicol quite toxic?

A

Nitro group

42
Q

What is chloramphenicol drug interactions?

A

Inhibits CYP 2C19 + 3A4
= tricyclic antidepressants, PPIs, macrolide antibiotics

43
Q

Why should lincosamides not be given simultaneously with macrolides + chloramphenicol?

A

Similar mechanism on action to them
= cause antagonism + possible cross-resistance

44
Q

Describe oxazolidinones

A

Bacteriostatic/cidal against gram +

45
Q

How does oxazolidinones inhibit protein synthesis?

A

Binds to 50S subparticle
= before 30S + 50S complex is formed
= stops ribosome forming

46
Q

What are antibiotics that inhibit nucleic acid transcription + replication?

A

Quinolones + fluroquinolones

47
Q

Describe quinolones + fluroquinolones

A

Bactericidal
Gram +/-

48
Q

How do quinolones + fluroquinolones inhibit nucleic acid transcription + replication?

A

Stabilising complex formed between DNA + topoisomerases

49
Q

What are drug interactions for quinolones + fluroquinolones?

A

Complex metal ions = antacids
Theophylline
Digoxin

50
Q

Which antibiotic caused injury to plasma membrane?

A

Polymixin B

51
Q

Describe polymixin

A

Gram - active

52
Q

How does polymixin cause injury to plasma membrane?

A

Bind to phosphate groups in bacterial membranes

53
Q

Which antibiotics inhibit synthesis of metabolites?

A

Sulphonamides + trimethoprim

54
Q

Are sulphonamides + trimethoprim bactericidal or bacteriostatic?

A

Bacteriostatic

55
Q

How does sulphonamides + trimethoprim inhibit synthesis of metabolites?

A

Act as competitive inhibitors of dihydropteroate synthetase
Block biosynthesis of tetrahydrofolate

56
Q

What are the adverse drug reactions of sulphonamides + trimethoprim?

A

Fever
Skin rashes
Allergic myocarditis

S2 Case 2 - Diarrhoea (12 decks)

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