Aminoglycosides - Gentamicin

Question 1

What is gentamicin used for?

Answer 1

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

Question 2

What bacteria is gentamicin particularly effective against?

Answer 2

• gram - negative aerobes
  including Pseudomonas aeruginosa

(severe infections)

Question 3

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

Answer 3

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

Question 4

How do aminoglycosides like gentamicin work?

Answer 4

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

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

Question 5

What is the spectrum of activity of aminoglycosides like gentamicin>

Answer 5

• Gram negative aerobic bacteria
• staphylococci
• mycobacteria

Question 6

How do aminoglycosides such as gentamicin enter the bacterial cell?

Answer 6

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

Question 7

Why are aminoglycosides inneffective towards streptococci and anaerobic bacteria?

Answer 7

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,

Question 8

How do penicillins enhance gentamicin uptake?

Answer 8

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

Question 9

What are the side effects of gentamicin?

Answer 9

• nephrotoxicity
• ototoxicity

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

Question 10

How does gentamicin cause nephrotoxicity and ototoxicity?

Answer 10

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

Question 11

How does nephrotoxicity present?

Answer 11

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

Question 12

How does otoxicity present?

Answer 12

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

Question 13

How are aminoglycosides excreted?

Answer 13

renally excreted

Question 14

Who are most susceptible to renal / ototoxicity?

Answer 14

Monitor levels of aminoglycosides carefully in:

• elderly
• neonates
• renal impairment

Question 15

why are aminoglycosides contraindicated in myasthenia gravis?

Answer 15

aminoglycosides can impair neuromuscular transmission.

Question 16

What are the drug interactions of gentamicin?

Answer 16

Ototoxicity risk increased with:

• loop diuretics
• vancomycin

Nephrotoxicity risk increased with:

• ciclosporin
• cephalosporin
• vancomycin
• platinum chemotherapy

Question 17

How is gentamicin taken>

Answer 17

IV

Question 18

what is the dose interval?

Answer 18

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

Question 19

how are aminoglycosides administered?

Answer 19

IV
diluted in 0.9% NaCl
infused slowly over 30 mins

Question 20

When can the 2nd dose of gentamicin be administered?

Answer 20

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

Question 21

How is gentamicin dose calculated?

Answer 21

dose depends on renal function and weight.

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