Antibiotics

Question 1

Which drug class is gentamicin in?

Answer 1

Aminoglycosides, alongside tobramycin, streptomycin, neomycin, amikacin.

Question 2

Gentamicin - Which bacteria is it inactive or have poor activity against?

Answer 2

Inactive: anaerobes

Poor activity: haemolytic streptococci and pneumococci

Question 3

Gentamicin - C/I

Answer 3

Myasthenia gravis - aminoglycosides can impair neuromuscular transmission
Perforated ear conditions - enhanced risk of ototoxicity

Question 4

Gentamicin - dosages

Answer 4

• correct any dehydration before treatment initiation to lower susceptibility of kidneys to impairment
• doses are based on renal function and body weight
• dose adjustments dependent on serum concentrations
• treatment shouldn’t exceed 7 days

Question 5

Gentamicin - renal impairment

Answer 5

CrCL < 20mL/min - avoid OD dosing in adults and children

- if it’s not too severe but still impaired - increase dosing intervals.

Question 6

Gentamicin - formulations

Answer 6

PF intrathecal preps - only for intrathecal or intraventricular use

Question 7

Gentamicin - KEY SE’s

Answer 7

• ototoxicity - irreversible due to gentamicin accumulation within the ear
• nephrotoxicity - reversible - common in renal impairment and elderly
• skin reactions
• tinnitus
• N/V
• Abx associated colitis

Question 8

Gentamicin - monitoring

Answer 8

• renal function - before initiating and during treatment
• serum-aminoglycoside conc - MUST in obesity and elderly
• auditory and vestibular function
• CRP, WBC
• monitor for histamine related reaactions
• temperature - if pt had pyrexia

Question 9

Gentamicin - interactions

Answer 9

• Ototoxic drugs: vancomycin, loop diuretics
• nephrotoxic drugs: cephalosporins, vancomycin ciclosporin, platinum chemotherapy
• Histamine drugs

Question 10

Gentamicin - dose adjustment in obesity

Answer 10

Aminoglycosides are hydrophilic, but obese pts have an excess fatty adipose tissue. This means high amounts of aminoglycosides accumulate in the blood which can be toxic.

Dose should be determined using ABW or CBW, NOT IBW.

Monitor serum-gentamicin conc in obese pts closely.

Question 11

Gentamicin - therapeutic drug monitoring in adults (multiple dosing in endocarditis)

Answer 11

Peak conc after 1h: 3 - 5 mg/L

Pre-dose trough: <1mg/L

Question 12

Gentamicin - therapeutic drug monitoring (IV/IM multiple dosing)

Answer 12

Peak conc, after 1h: 5-10mg/L

Pre-dose trough: <2mg/L

Question 13

Linezolid - drug class?

Answer 13

Oxazolidinone - targets protein synthesis and binds to the 50S subunit