Gentamicin assays for patients on conventional divided doses (tds or bd) or other regimens: Target range and Results interpretation.

Pre-dose level

• The pre-dose level must be low to minimise toxicity.
• The target range is <2 mg/L.
• Remember that apparently high levels may be due to miss-timing of the samples.

• Normal pre-dose level:
  • The regimen can be continued. 
  • Further "pre-dose" level should be monitored twice weekly  so long as renal function is stable.
• Pre-dose level is between 2-3 mg/L (and renal function unchanged)
  • Increase the dosing interval e.g. from tds to bd.
• Pre-dose level is >3 mg/L 
  • Further gentamicin doses should be withheld until discussed with microbiology  
  • The need for gentamicin therapy should be reviewed.

Post-dose level

• The post-dose level must be adequate to ensure efficacy.
• For most infections the target range is 5-10 mg/L.
• For serious pseudomonas infections the target range is 7-10 mg/L.
• For streptococcal or enterococcal infections eg endocarditis the target range is 3-5 mg/L.
• Post dose level is below the target range
  • Gentamicin is sub-therapeutic. 
  • The dose must be increased. 

Pre- and post-dose levels.

• Post-dose level is above the target range; pre-dose is normal
  • Reduce the dose.
• Both the post-dose and pre-dose levels are above the target range
  • The  next dose(s) should be omitted.
  • The need for further gentamicin should be reviewed. 
  • For further gentamicin therapy the interval between doses must be increased after discussion with microbiology.

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Page last edited: 29/10/2008

Caution; the antibiotic doses recommended on this website are intended for adult patients with normal renal and liver function unless otherwise stated. Dosing advice for patients with renal impairment is available here.

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