Gentamicin dosing in infective endocarditis in adults (Antimicrobial)

Warning

Audience

  • Argyll & Bute HSCP and Highland HSCP
  • Primary and Secondary Care.

This policy covers the use of intravenous (IV) gentamicin for the treatment of infective endocarditis in adults. The policy is for the use of gentamicin for the treatment of infection only. Recommendations on gentamicin dosing for surgical prophylaxis are on TAM. This policy should not be used for patients established on renal replacement therapy or in those with an eGFR of less than 21mL/min. Discuss suitable alternatives with microbiology.

Gentamicin is used in the management of infective endocarditis caused by Gram-positive or certain Gram-negative organisms; however the dosing regimens differ depending on the organism. Until the organism has been identified, follow the dosing recommendations for Gram-positive organisms, unless advised otherwise by an infection specialist.

For Gram-negative organisms, the standard, high dose (ie 5mg/kg/dose) gentamicin guideline should be used. This policy is available on TAM along with the online dose calculator and prescription chart. High dose gentamicin protocols have no current proven efficacy in the management of Gram-positive endocarditis and therefore should not be used.

For Gram-positive organisms, the addition of low dose (ie 3 mg/kg/dose) once daily gentamicin to a penicillin or beta-lactam antibiotic is synergistic and results in a more rapid bactericidal effect. Prescribe on the normal NHS Highland drug chart; do not use the gentamicin prescribing, administration and monitoring form to prescribe synergistic gentamicin.

Dosage guidelines for synergistic gentamicin

These guidelines aim to produce a trough of < 1 mg/L. Doses of up to 300mg can be given as a bolus injection over 3 to 5 minutes; higher doses should be administered as a short infusion over 30 minutes. This will not alter interpretation of trough levels.

Weight banded dosing is given in the table below. Doses must be calculated using maximum body weight if patients are obese (actual weight more than 20% of Ideal Body Weight) (see maximum body weight table).

Weight [actual (or maximum body weight if obese)] Dose of Gentamicin
43kg to 49kg  140mg 
50kg to 56kg  160mg 
57kg to 64kg  180mg 
65kg to 70kg  200mg 
71kg to 76kg  220mg 
77kg to 82kg  240mg 
83kg to 88kg  260mg 
89kg to 96kg  280mg 
97kg to 100kg  300mg 
101kg to 109kg  320mg 
110kg to 115kg  340mg 

Maximum body weight table

Use to determine dosing weight for obese patients (defined as actual weight more than 20% of Ideal Body Weight)

Maximum body weight table 
Height (ft inches)  Height (cm)  MBW (kg) (male)  MBW (kg) (female)
4'8" 142 49 43
4'9" 145 52 47
4'10" 147  54  49 
4'11" 150  58 52 
5'0" 152 60 55
5'1" 155 62 58 
5'2" 158 66  60
5'3" 160 68 62 
5'4" 163  71 66 
5'5" 165  74  68 
5'6" 168  77 71 
5"7  170  79  74 
5'8"  173  82  77 
5'9"  175  85  79 
6'0" 183  94  88 
6'1" 185  96  90 
6'2" 188  98  94 
6'3" 191  101  97 
6'4" 193  104  99 
6'5"  195  107  101 
6'6" 198  109  105 
6'7"  201  113  108 
6'8"  203  115  110

Monitoring

  1. Take a blood sample for gentamicin analysis at the end of the first dosage interval (trough concentration) then give the next dose. Do not delay giving the second gentamicin dose while waiting for trough concentration.
  2. If the gentamicin trough is <1mg/L, continue the present dosage regimen.
  3.  Record the exact time of gentamicin samples on the sample request form.
  4.  Seek advice from pharmacy if you are unsure how to interpret the result or if the concentrations are not within range.
  • Monitor renal function and gentamicin trough levels daily for the first three days.
  • If renal function is stable, check the trough concentration every 3 days.
  • If renal function deteriorates, check the trough daily.

If the gentamicin trough concentration is >1mg/L and a further dose has been administered, re-analyse the trough after the next dose. Do not give a further dose until the gentamicin concentration is <1mg/L.

Suggested dose adjustment for serum levels out with range

High Trough: 

  • Increase dosage interval. Extension of the dose interval would normally be from 24 hourly to 48 hourly.
  • Discuss with pharmacy if subsequent levels remain out with range

Gentamicin duration

Gentamicin therapy should continue for 2 weeks except in the case of enterococcal infective endocarditis (IE) when it may be given for 2 to 6 weeks on Infection Specialist advice.

Ongoing monitoring and signs of toxicity

Renal toxicity

  • Monitor creatinine daily. Seek advice if renal function unstable (eg change in creatinine of >15%).
  • Signs of renal toxicity include increase in creatinine.
  • Falling urine output or oliguria will lead to accumulation of gentamicin and increase the risk of toxicity.
  • Consider an alternative agent if creatinine is rising or the patient becomes oliguric.

Ototoxicity

  • Ototoxicity secondary to gentamicin is independent of drug concentration. It is suggested by any of the following: new tinnitus, dizziness, poor balance, hearing loss or oscillating vision.
  • Toxicity is associated with prolonged aminoglycoside use (usually >10 days but may be >72 hours) and is secondary to drug accumulation within the inner ear.
  • Stop treatment if ototoxicity is suspected and refer to microbiology or an infection specialist for advice on future therapy.
  • If gentamicin is to continue for more than 7 days, consider referring to audiology for assessment.

Last reviewed: 27/10/2022

Next review date: 31/10/2025

Author(s): Antimicrobial Management Team.

Approved By: Approved TAMSG of the ADTC

Reviewer name(s): Alison Macdonald, Antimicrobial Pharmacist, .

Document Id: AMT134

Related resources

Further information for healthcare professionals 

  1. European Cardiology Society guidance published in 2015 
  2. American Heart Association Guidance 2015
  3. Guidelines for the diagnosis and antibiotic treatment of endocarditis in adults: a report of the Working Party of the British Society for Antimicrobial Chemotherapy J Antimicrob Chemother 2012; 67: 269–28
  4. NHS Greater Glasgow and Clyde Clinical Guideline: Synergistic Gentamicin for Endocarditis in Adults. Version 2 published 06/07/2016. Accessed online 09/04/2019. 
References

Self-management information

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