Aminoglycosides - Gentamicin Flashcards

1
Q

What is gentamicin used for?

A
  • sever sepsis (unidentified source)
  • pyelonephritis and complicated UTI
  • biliary and intra-abdo sepsis
  • endocarditis
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2
Q

What bacteria is gentamicin particularly effective against?

A
  • gram - negative aerobes
    including Pseudomonas aeruginosa

(severe infections)

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3
Q

Why are aminoglycosides like gentamicin combined with penicillin and/or metronidazole?

A

Aminoglycosides like gentamicin have no activity against streptococci and anaerobes so should be combined with penicillin and metronidazole when the organism is unkown.

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4
Q

How do aminoglycosides like gentamicin work?

A

They are bactericidal- bind irreversibly to bacterial ribosomes (30S subunit) and inhibit protein synthesis.

They enter bacterial cells via an oxygen-dependant transport system.

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5
Q

What is the spectrum of activity of aminoglycosides like gentamicin>

A
  • Gram negative aerobic bacteria
  • staphylococci
  • mycobacteria
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6
Q

How do aminoglycosides such as gentamicin enter the bacterial cell?

A

Gentamicin enters bacterial cells via an oxygen-dependant transport system.

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7
Q

Why are aminoglycosides inneffective towards streptococci and anaerobic bacteria?

A

Aminoglycosides enter the bacterial cell via oxygen-dependant transport system. They then bind to 30S subunits and prevent protein synthesis.
Streptoccoci and anaerobes dont have this oxygen dependant transport system,

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8
Q

How do penicillins enhance gentamicin uptake?

A
  • some baceria acquire resistance to aminoglycosides by reducing cell membrane permeability.
  • Penicillins help uptake of gentamicin by weakening the bacterial cell walls.
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9
Q

What are the side effects of gentamicin?

A
  • nephrotoxicity
  • ototoxicity

(aminoglycosides accumulate in renal tbubular epithelial cells and cochlear/vestibular hair cells and trigger apoptosis and cell death)

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10
Q

How does gentamicin cause nephrotoxicity and ototoxicity?

A

Gentamicin accumulates in the renal tubular epithelial cells and the cochlear/vestibular cells - here they trigger apoptosis and cell death.

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11
Q

How does nephrotoxicity present?

A
  • reduced urine output
  • rising serum creatinine
  • risinf urea
    (can be reversible
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12
Q

How does otoxicity present?

A
after acute infection cleared
- hearing loss
- tinnitus
- vestibular damage
(may be irreversible)
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13
Q

How are aminoglycosides excreted?

A

renally excreted

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14
Q

Who are most susceptible to renal / ototoxicity?

A

Monitor levels of aminoglycosides carefully in:

  • elderly
  • neonates
  • renal impairment
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15
Q

why are aminoglycosides contraindicated in myasthenia gravis?

A

aminoglycosides can impair neuromuscular transmission.

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16
Q

What are the drug interactions of gentamicin?

A

Ototoxicity risk increased with:

  • loop diuretics
  • vancomycin

Nephrotoxicity risk increased with:

  • ciclosporin
  • cephalosporin
  • vancomycin
  • platinum chemotherapy
17
Q

How is gentamicin taken>

A

IV

18
Q

what is the dose interval?

A

24hr normal renal function or 36-48hrs renal impairment.

19
Q

how are aminoglycosides administered?

A

IV
diluted in 0.9% NaCl
infused slowly over 30 mins

20
Q

When can the 2nd dose of gentamicin be administered?

A

Check the plasma drug conc after 18-24hrs from the first dose. The next dose should only be given once the gentamicin plasma con has fallen to a safe level e.g. <1mg/ml

21
Q

How is gentamicin dose calculated?

A

dose depends on renal function and weight.

**in obese patients go according to ideal weight for height.