Gentamicin Dosing in Patients with Bacterial Endocarditis

1. Gentamicin is used in bacterial endocarditis for synergy with other antimicrobial agents. Gentamicin doses and target AUC are generally lower than for other indications.
2. At CDHB, most patients receive gentamicin once daily for bacterial endocarditis. Infectious Diseases may sometimes advise that the daily dose is given in two or three divided doses.
3. All doses should be prescribed in MedChart with frequency set as "variable" dose.
4. For once daily dosing:
   1. Calculate the initial dose of IV 3 mg/kg ideal body weight once daily.

      Ideal body weight

      Height	Ideal body weight (M/F)
      150 cm	50 kg / 46 kg
      152 cm	52 kg / 47 kg
      155 cm	55 kg / 50 kg
      157 cm	56 kg / 52 kg
      160 cm	59 kg / 55 kg
      163 cm	62 kg / 57 kg
      165 cm	64 kg / 59 kg
      168 cm	66 kg / 62 kg
      170 cm	68 kg / 64 kg
      173 cm	71 kg / 66 kg
      175 cm	73 kg / 68 kg
      178 cm	75 kg / 71 kg
      180 cm	77 kg / 73 kg
      183 cm	80 kg / 75 kg
      185 cm	82 kg / 77 kg
      188 cm	84 kg / 80 kg
      191 cm	87 kg / 83 kg

        

   2. Give by IV infusion over 30 minutes in 100 mL of sodium chloride 0.9%.
   3. Document start and finish times of infusion to help with dose predictions.
   4. After the first dose, take two blood samples for gentamicin concentrations:
      1. 30 minutes after the end of infusion, and
      2. 6 to 8 hours after the end of the infusion.
5. For daily divided doses (only if advised by Infectious Diseases):
   1. Calculate the initial dose of IV 1 mg/kg ideal body weight every eight hours (if changing from once daily dosing, consult ward pharmacist).

      Ideal body weight

      Height	Ideal body weight (M/F)
      150 cm	50 kg / 46 kg
      152 cm	52 kg / 47 kg
      155 cm	55 kg / 50 kg
      157 cm	56 kg / 52 kg
      160 cm	59 kg / 55 kg
      163 cm	62 kg / 57 kg
      165 cm	64 kg / 59 kg
      168 cm	66 kg / 62 kg
      170 cm	68 kg / 64 kg
      173 cm	71 kg / 66 kg
      175 cm	73 kg / 68 kg
      178 cm	75 kg / 71 kg
      180 cm	77 kg / 73 kg
      183 cm	80 kg / 75 kg
      185 cm	82 kg / 77 kg
      188 cm	84 kg / 80 kg
      191 cm	87 kg / 83 kg

        

   2. Give by IV infusion over 30 minutes in 100 mL of sodium chloride 0.9%.
   3. Document start and finish times of infusion to help with dose predictions.
   4. On either side of (before and after) the third dose, take two blood samples for gentamicin concentrations:
      1. Trough sample just before (within 30 minutes of) the third dose,
      2. Peak sample at 30 minutes after the end of the third dose infusion.
6. Contact the ward pharmacist during normal working hours with the drug concentration results to get a prediction for the next dose. Alternatively, contact the pharmacist on call after hours (call before 10.30 pm unless the dose must be given before 8 am). The concentration targets are an AUC (24 hours) of 30 – 50 mg/L.hr and trough concentration of < 0.5 mg/L for once daily dosing, and a peak of 3 – 4 mg/L and a trough < 1 mg/L with daily divided doses.
7. Repeat blood sampling as outlined in 4) and 5) above for gentamicin concentrations every 3 days. This may need to be more or less frequent depending on the clinical situation.
8. Monitor renal function. If it is changing, dose alteration will be required – contact the ward pharmacist. Stop therapy if hearing or vestibular function appears to be affected.
9. The Department of Infectious Diseases must be consulted for any patient being sent home on aminoglycosides for ongoing monitoring. Contact Medicines Information (03 364 0900) for dose predictions for these patients.

Topic Code: 607895

must be prescribed or recommended by a consultant.