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Year 5 > Antimicrobial agents > Flashcards

Antimicrobial agents Flashcards

1
Q

Which drugs target bacterial cell wall synthesis?

A
  • Beta-lactams (Penicillins, Cephalosporins, Carbapenems)

- Glycopeptides (Vancomycin)

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2
Q

How do Beta-lactams work?

A

By binding to penicillin-binding proteins (PBPs), e.g. transpeptidase, prevent the formation of peptide cross-links in daughter cell walls
The daughter cells are therefore weak and prone to osmotic lysis.
They are effective against rapidly dividing bacteria.
They are not effective against bacteria which lack a cell wall e.g. Mycoplasma.

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3
Q

Penicillin

A 
Penicillin is the most active Beta-lactam.
It covers Gram +ve organisms including
- Staph
- Strep
- Clostridium

It is broken down by B-lactamases from
- S. aureus

Pharmacokinetics

  • TIME-DEPENDENT killing
  • Give 3-4 doses per day
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4
Q

Flucloxacillin coverage

A 
Flucloxacillin is a narrow-spectrum antibiotic.
It covers
- Staph
- Strep
- Clostridia

It is STABLE to Beta-lactamases from S. aureus and is therefore the mainstay of S. aureus infection.

It is less active than penicillin

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5
Q

Amoxicillin

A 
Amoxicillin is a broad-spectrum antibiotic.
It covers
- Staph
- Strep
- Enterococi
- Some G-ve organisms

It is broken down by beta-lactamases from

  • S. aureus
  • E. coli

it can be made stable to beta-lactamased by addignf clavulanic acid (This is Co-amoxiclav, aka Augmentin)

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6
Q

Piperacillin

A 
Piperacillin is a broad-spectrum antibiotic
it covers:
- Staph
- Strep
- Some Gram -ves, including Pseudomonas

It is broken down by beta-lactams from:
- S. aureus
- E. coli
It can be combined with tazobactam to form tazocin, therefore stable to Beta-lactams.

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7
Q

Overview of cephalosporins

A

Cephalosporins are generally stable to beta-lactamases.
1st gen: Cefalexin
2nd gen: Cefuroxime
3rd gen: Ceftazidime, Ceftriazone and Cefataxime

As you go up the generations there is more G-ve coverage and less G+ve coverage

Cefuroxime has no G+ve coverage except for E. coli, whereas Ceftazidime has only G-ve coverage.

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8
Q

Cefuroxime

A

2nd gen,
Cefuroxime covers the same as co-amoxiclav

It is stable to many B-lactamases produced by G-ves

It is combined with metronidazole to treat anaerobic infections.

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9
Q

Ceftriaxone

A

3rd gen

  • Ceftriaxone covers G+ve and G-ve organisms including NHS organisms (N. meningitidis, Haemophilus and S. pneumoniae)
  • It is the mainstay of treatment for meningitis
  • IM ceftriaxone is given for gonorrhea

Caution:

  • It can cause C. difficile infection, so reserve for serious infection and avoid in the elderly
  • Do not use in neonates, as it can displace bilirubin form albumin and cause biliary sludging
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10
Q

Beta-lactams - metabolism

A

Metabolised in kidneys

Can be nephrotoxic (renal tubular acidosis)

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11
Q

Carbapenems

A

Stable to ESBLs
e.g. Meropenem
Can be used for MRSA

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12
Q

Ceftazidime

A

Covers G-ve only including Pseudomonas

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13
Q

Glycopeptides

A

MOA - bind to amino-acid chain on peptidoglycan precursor, this blocks formation of glycosidic bonds.

Cover G+ve only (because they cannot penetrate G-ve)
Vancomycin can be used for:
- MRSA (IV)
- C. difficile (PO)

Pharmacokinetics

  • Both time-dependent and concentration-dependent killing, so do infusion
  • NEED TO MONITOR LEVELS, as it is nephrotoxic.
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14
Q

Aminoglycosides

A

Inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit.
Covers gram negatives and all ESBLs.

Uses:
- Gram negative sepsis

Caution:

  • Need to monitor levels due to ototoxicity and nephrotoxicity
  • Inhibited by low pH (e.g. in abscesses)

Pharmacokinetics

  • They have CONCENTRATION-DEPENDENT killing effects, so give ONE BIG DOSE per day.
  • Monitor the TROUGH level after 24h to see if toxic levels have accumulated.
  • If so, adjust frequency
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15
Q

Tetracycline

A

Inhibits bacterial protein synthesis by blocking the binding of aminoacyl-tRNA to the 30S ribosomal subunit.

Coverage: G+ve (most G-ve bugs are resistant to tetracycline)

Uses:

  • Oral treatment for MRSA
  • Intracellular pathogens e.g Chlamydia
  • Staph and Strep

Caution:

  • Deposited in growing bone
  • Discolouration of teeth
  • Light sensitive rash
  • Contra-indicated in pregnancy and in children
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16
Q

Macrolides

A
  • Bind to the 50S subunit of the bacterial ribosome
  • Erythromycin is given 4x daily; clarithromycin and azithromycin are given less often

Coverage

  • Mainly G+ve
  • Azithromycin has some G-ve coverage

Uses

  • Staph and Strep infections in penicillin-allergic
  • Also useful in Campylobacter (although this is usually self-resolving), Legionella and Helicobacter infections

Caution

  • Limited use in sepsis as they are bacteriostatic
  • Macrolide resistance can confer clindamycin resistance
17
Q

Chloramphenicol

A
  • Broad spectrum
  • Binds to peptidyl transferase of the 50S subunit

Coverage:
- Good coverage against Pneumococcus

Uses

  • Eyedrops for bacterial conjunctivitis
  • Meningitis treatment in penicillin-anaphylactic

Side-effects

  • Aplastic anaemia
  • Grey baby syndrome
18
Q

Linezolid

A
  • Broad-spectrum
  • Binds to 23S subunit of the 50S ribosomal subunit, which blocks to formation of 70S, therefore blocking translation

Uses
- Gram +ve, including MRSA and VRE

Caution

  • Can cause thrombocytopenia
  • Optic neuritis
  • Expensive, so use only with microbiology approval
19
Q

Fluoroquinolones

A

MOA - block alpha subunit of DNA gyrase

Coverage

  • Ciprofloxacin covers Pseudomonas and other G-ve organisms
  • Levofloxacin and Moxifloxacin cover G+ve coverage, they do not cover Pseudomonas

Uses

  • Bacterial UTI
  • Bacterial gastroenteritis
  • Atypical pneumonia

NB these are well absorbed after oral administration.

20
Q

Nitromidazoles

A
  • Produce an active intermediate which causes DNA breakage

Metronidazole

  • Covers anaerobes and protozoa (e.g. Giardia)
  • However infections are never purely anaerobic, so combine with another antibiotic e.g. cefuroxime
21
Q

Nitrofurans

A
  • Related to nitromidazoles
  • Covers E. coli, used in lower UTI
  • Concentrates in bladder
  • Needs contact time with bladder, so take after voiding
  • Not suitable for catheter-associated UTI
22
Q

Rifampicin

A
  • Belongs to rifamycin class
  • Inhibitor of DNA-dependent RNA polymerase

Uses

  • Mycoplasma (TB)
  • Chlamydia
  • Legionella
  • Staph and Strep

Caution

  • Metabolised in liver, so monitor LFTs
  • Can interact with other liver-metabolised drugs
  • Orange urine, faeces and contact lenses

Resistance

  • Resistance develops quickly (from a single amino acid change) so do not use as a single agent
  • The exception is prophylaxis for close contacts in meningitis infection
23
Q

Inhibitors of folate metabolism

A

Sulfomethoxazole + Trimethoprim (co-trimoxazole, e.g. Septrin)
- Used in PCP, toxoplasmosis and G-ve organisms

Trimethoprim

  • Can be used for lower UTI, but 40% E.coli is resistant
  • Cannot be used in the first trimester of pregnancy
24
Q

Daptomycin

A
  • Cell membrane toxin
  • Cyclic lipopeptide
  • Gram positive coverage only
  • MRSA and VRE
  • Specific conditions only, so seek microbiology advice
25
Q

Colistin

A
  • Cell membrane toxin
  • Polymyxin antibiotic
  • Covers Gram -ves only
  • Pseudomonas, Klebsiella
  • IV only
  • Not particularly active
  • Nephrotoxic - so monitor levels
26
Q

Mechanisms of Resistance

A

“BEAT”
BYPASS steps of pathway

ENZYME-mediated inactivation

  • Beta-lactams
  • ESBLs
  • Carbapenemases (OXA-48 is commonest)

ACCUMULATION of drug is impaired

TARGET altered

  • MRSA:
  • mecA gene is acquired encoding a novel PBP2a
  • Beta-lactams cannot bind to this
27
Q

Factors influencing antibiotic choice

A

CHAOS:
Choice of antibiotic depends on

HOST factors
ANTIMICROBIAL susceptibility
SITE of infection

28
Q

What is the minimum inhibited concentration (MIC)?

A

The minimum concentration of antibiotic required to stop growth of the organism in culture.
Aim for Low MIC

29
Q

When should you switch from IV to PO in hospital?

A

Once patient has stabilised after 48h of IV therapy

30
Q

What influences dosing considerations?

A
  • Peak above the MIC (aminoglycosides)
  • Time above the MIC (penicillin)
  • Area below curve, above MIC (vancomycin)

Year 5 (22 decks)

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