M15- Antibiotics Flashcards

1
Q

what is an antibiotic?

A

a drug used to treat or prevent infection caused by micro-organisms

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2
Q

what is bacteriostatic?

A

inhibit growth of bacteria

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3
Q

what is bactericidal?

A

kill bacteria

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4
Q

How can antibiotics be narrow spectrum or broad spectrum?

A

-e.g. Penicillin narrow spectrum active against Gram-positive bacteria
• Tetracycline active against many Gram-positive & Gram-negatives

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5
Q

what are antibiotics not a substitute for?

A

functional immune system

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6
Q

what are features of an ideal antibiotic?

A
•  Selective toxicity/minimal toxicity to host 
•  Cidal
–  (i.e. kills bacteria) 
•  Long half life
–  (e.g. low binding to plasma proteins)
•  Appropriate tissue distribution
•  No adverse drug interactions/side effects
 •  Oral & parenteral preparations
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7
Q

Name 3 antibiotic targets.

A
  • cell wall (peptidoglycan synthesis)
  • ribosomes (protein synthesis)
  • DNA replication (nucleic acid synthesis)
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8
Q

what is cell wall synthesis targeted by?

A

ß-lactam (penicillins) & Glycopeptide antibiotics

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9
Q

How does penicillin work?

A

prevents cross linking of bacterial cell wall

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10
Q

Name 3 beta-lactams.

A
  • Penicillin V (narrow spectrum)
  • Amoxicillin (entended spectrum)
  • Co-amoxiclav (inhibits b-lactamase)
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11
Q

What is the main B-lactams prescribed by dentists?

A

amoxycillin

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12
Q

what are features of amoxycillin?

A
  • spectrum extended
  • absorbed through intestine
  • stable in presence of stomach acid
  • peak plasma concentration 60-120 minutes after taking
  • wide tissue distribution
  • 20% binds to plasma proteins
  • plasma half life is 60 minutes
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13
Q

what is not suitable for empiric prescribing?

A

co-amoxiclav

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14
Q

what are the features of penicillin V?

A
  • narrower spectrum
  • absorbed through intestine
  • sensitive to stomach acid
  • peak plasma concentration 30-60 minutes aft6er taking
  • 75%-90% binds to plasma proteins
  • serum levels maintained for 30-60mins
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15
Q

what are the advantages of B-lactam antibiotics?

A

– Well characterised
– Safe
– Spectrum (narrow to wide)
– Variety/choice

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16
Q

what are the disadvantages of B-lactam antibiotics?

A

– Resistance
– Rapidly excreted
– Hypersensitivity (1-10%) – CDI (C. diff infections)

17
Q

what is the caution when using B-lactam antibiotics?

A
  • Antibiotic antagonism

- Penicillin & bacteriostatic antibiotics

18
Q

what are not B-lactam antibiotics but similar mode of action ?

A

Glycopeptides

19
Q

How does glycopeptides work?

A

• Cell-wall active antibiotics,
– Binds to end of peptide side chains (D-alanine D-
alanine) & prevent its incorporation into the cell wall.
– Blocks access to substrate by PBP (transpeptidase)
– Inhibits peptidoglycan synthesis,
– Reduced cross-linking & activity of lytic enzymes
weaken the bacterial cell wall
• Bactericidal

20
Q

Name some antibiotics that target protein synthesis?

A
  • tetracyclines - deoxycycline

- macrolides - erythromycin

21
Q

Name the features of gentamicin (aminoglycosides).

A
  • not absorbed from gut -intravenously
  • binds to ribosomes inhibiting protein synthesis: bactericidial
  • active against gram negative
  • excreted in urine
  • toxicity -so monitored blood levels
22
Q

what is the mode of action of tetracyclines (bacteriostatic ) ?

A

Actively transported into cell. Binds to 30S subunit. Prevents attachment of tRNA to acceptor sites. Stops chain elongation

23
Q

what are the adverse effects of tetracyclines?

A

Destruction of normal intestinal flora resulting in increased secondary infections

24
Q

what is the mode of action of lincosamides (bacteriostatic)?

A

– Bind to the 50S ribosome. Blocks Peptidyl-transferase.

– Prevents peptide Bond Synthesis.

25
what does the macrolides (erythromycin ) group do/
- excreted via the liver, biliary tract and into the gut. – not excreted in urine - Lipophilic antibiotics pass through cell membranes easily. – They are useful for treating certain infections where intracellular bacteria “hide” from the host’s immune system – Erythromycin is safe in pregnancy
26
Name an antibiotic that inhibits nucleic acid synthesis?
metronidazole | -anaerobes and protozoa
27
How does metronidazole work ?
anaerobic conditions important beacuse its taken up into cell into inactive form - in reducing conditions becomes activated (charged molecule) -interfere and causes damage to DNA and leads to death
28
what is the mode of action of Quinolones (bactericidal)?
Bind to the A subunit of DNA gyrase (topoisomerase) and prevent supercoiling of DNA. Indirectly inhibit DNA synthesis
29
Name some side effects of antibiotics.
• Nausea, vomiting, diarrhoea – common – all antibiotics disrupt the gut bacterial flora – may affect absorption of oral contraceptives • Gentamicin – renal & VIII nerve damage • Metronidazole – interacts with alcohol • Broad spectrum antibiotics increase the risk of C. difficile infection in the elderly
30
what are the 4 "C" antibiotics that we try avoid using and why?
``` These broad-spectrum antibiotics are particularly associated with an increased risk of Clostridium difficile (“C diff”) infection: – Cephalosporins – Co-amoxiclav (MAIN) – Ciprofloxacin – Clindamycin ```