Gentamicin

• Baseline renal function should be measured, and creatinine clearance calculated.
• Monitor renal function daily.  If there is a greater than 15% change in serum creatinine re-calculate creatinine clearance and adjust dose. 
• Take a baseline weight and then monitor weekly. Adjust dose if weight changes. 
• Take daily U+Es.
• Monitor serum gentamicin levels (see below). 
• Auditory function may be affected. Please refer to Audiometry and intravenous aminoglycosides. 

Where possible, creatinine clearance should be calculated before deciding the dosing of gentamicin. 

The EPR gentamicin calculator will launch automatically when gentamicin is prescribed. This calculator will calculate the dosing weight. In order to do this, an accurate weight and height will need to be entered on EPR. This calculator will calculate a dose and rounds down to the nearest 20mg. This calculator is capped with a maximum dose of 480mg.

gentamicin 5mg/kg: dose should be capped at maximum dose of 480mg. 

gentamicin 3mg/kg (for both surgical prophylaxis and patients with reduced creatinine clearance): dose should be capped at a maximum dose of 240mg

For Adult Critical Care areas that use CareVue, or in the case of EPR downtime, use the following guideline (On OUH Intranet): EPR Downtime Guide 

STEP 1. Determine Creatinine Clearance (CrCl)

Use Estimated Creatinine Clearance calculator on EPR. Note that there are two calculators (male and female) so chose appropriate calculator.

OR

Determine Creatinine Clearance (CrCl) using the Cockcroft-Gault equation (below).

CrCl (mL/min) = F x (140-age) x weight (kg)   

                             Serum Cr (micromol/L)

where F=1.04 (females) or F=1.23 (males)

• Use Ideal Body Weight (IBW) if Actual Body Weight (ABW) is over 20% above IBW.
• In patients with low serum creatinine (less than 60 micromol/L), use 60 micromol/L to calculate creatinine clearance). 

STEP 2. Calculate initial gentamicin dose

STEP 3. Prescribe on EPR. The Gentamicin Calculator will launch automatically. 

Prescribers are required to ensure: 

1. Dosing weight and height is accurate or best estimate. 
2. Dose provided by calculator is in the expected range. 

Ensure that "Apply dose" is clicked to prescribe the dose on drug chart. For further information on how to use the calculator see: Gentamicin calculator - how to guide (v1.1).pdf 

NOTE: If actual body weight is less than ideal body weight, the EPR calculator will not calculate the dose. Prescribers need to:

1) Manually enter the patient's actual body weight into the box for 'Adjusted weight'. 

2) Change 'Adjustment' box to Actual (no adjustment) as shown in the example image below:

The calculator will now calculate the correct dose. 

STEP 4. Responding to gentamicin levels if creatinine clearance 31ml/min or greater 

• Take serum gentamicin level (yellow blood tube) 6-14 hours after administration of first dose of gentamicin. 
• Once level available, plot on nomogram below and adjust time interval as required. 
• If gentamicin level is not available at 24 hours post first dose: check table below for when to give the next dose (time interval)*. 

• For gentamicin 3 day courses: After calculating dosing interval from nomogram below:
  • • • If interval is 24 hours - give 2 further doses at the appropriate time.
      • If interval is 36 or 48 hours -  give 1 further dose at the appropriate time.
• For prolonged courses if renal function is stable, repeat gentamicin levels should be taken twice a week.
• Take daily U+E. If renal function is deteriorating review use of gentamicin as this is a nephrotoxic medicine.

   

Gentamicin 5mg/kg nomogram

* If gentamicin level is not available at 24 hours, suggested time intervals for 5mg/kg dose are:

STEP 4. Responding to gentamicin levels if creatinine clearance 30ml/min or less

• Take gentamicin level 24 hours after dosing. Continue taking levels every 12 hours until level is less than 1mg/L. Only re-dose once level is less than 1mg/L.
• For patients on a 3 day course the patient may only be given 1 dose if level remains above 1mg/L.
• Take daily U+E. 

Nomogram was adapted from the Lancashire NHS Foundation Trust gentamicin guideline