Paediatric: Gentamicin

General Information

This guideline is not for use in infants under 1 month - see neonatal guidance

This guideline is not for use in surgical prophylaxis - see individual guidance in prophylaxis section

Formulary antimicrobial: Use in accordance with Trust guidelines

Gentamicin is given intravenously or if this route is unavailable, by intramuscular injection. Contact paediatric pharmacists for further advice about intramuscular administration.
Gentamicin is not suitable for oral use.

Adverse effects:

Most adverse effects due to gentamicin are dose related and due to the narrow therapeutic index.
Use beyond 2 doses is for exceptional circumstances and should be discussed with Paediatric ID/Micro.
Irreversible vestibular and auditory damage, and nephrotoxicity are the most common adverse effects. They occur most frequently in those with renal impairment.

Cautions

Do not give gentamicin to patients with myasthenia gravis or a familial susceptibility to gentamicin toxicity.

Use nephrotoxic drugs with caution alongside gentamicin

e.g. ACE-inhibitor, diuretics (especially IV), NSAIDs, ciclosporin, colistimethate sodium, radio-contrast media, high-dose methotrexate or amphotericin B liposomal (Tillomed/Gilead/AmBisome)

Where gentamicin doses are being repeated, monitor serum creatinine and gentamicin levels - see below.

Gentamicin distributes into fat less well than into muscle. See below for dosing in obesity.

Mitochondrial mutations MHRA drug safety update (January 2021)

Evidence suggests an increased risk of aminoglycoside-associated ototoxicity in patients with certain mitochondrial mutations (particularly the m.1555A>G mutation), including cases in which the patient’s aminoglycoside serum levels were within the recommended range. These mitochondrial mutations are rare and frequency of complication is uncertain.

Genetic testing should not delay urgently needed aminoglycoside treatment but consider the need for genetic testing, particularly in those requiring recurrent or long-term treatment with aminoglycosides.

Where the patient has a susceptible mutation consider the need for aminoglycoside treatment versus alternative options.

If treatment is longer than 2 weeks, auditory testing should be performed at beginning and end of treatment. Test sooner if patient develops symptoms of deafness or vestibular dysfunction develops.

Patients should be advised to report immediately the onset of any sign of deafness or vestibular dysfunction

NB: For information for Audiometry assessment see Audiometry and intravenous aminoglycosides

Reference:

MHRA. Drug Safety update (January 2021) Aminoglycosides (gentamicin, amikacin, tobramycin, and neomycin): increased risk of deafness in patients with mitochondrial mutations. Accessed HERE

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STEP 1: Calculate the dosing weight (DW) i.e. weight that is used to calculate the gentamicin dose - this may differ from actual body weight

a) Obtain actual body weight in kg (ABW)

b) Calculate ideal body weight (IBW)

IBW is determined by first measuring the height of the child in centimetres and using that to identify the height centile for their age.

Length may need to be used if the child is too sick to stand up or if the child has some form of disability, or ask the parent/carer to provide a recent height estimate.

Their IBW weight is then selected according to the weight at the same centile as their height for their age. Use the UK WHO growth charts available on EPR for the determination of height and weight centiles.

Example of IBW calculation using Moore’s method

A 7 year old girl who is 1.2m tall and weighs 32kg

First : Identify the height centile using UK WHO growth charts : The height is around the 50th centile.

Then: Identify the weight at the 50th centile using UK WHO growth charts

50th centile weight for a 7 year old girl is 23kg.

c) Establish Dosing Weight (DW)

If the actual body weight (ABW) is within 20% of IBW then DW = ABW
If ABW is more than 20% above IBW then calculate the Dosing Weight using the following:

Dosing Weight in Kg = IBW + (0.35 x (actual body weight – IBW))

STEP 2: Determine the eGFR

Determine eGFR using the Modified Bedside Schwartz:

Child 1 month or over:

Estimated GFR (mL/min/1.73 m2) = 35 × height (cm) / serum creatinine (micromol/l)

Estimated glomerular filtration rate should be used with caution in very malnourished children or those with liver disease.

STEP 3a. Patient 1 month and over with eGFR over 90ml/min/1.73m²- Dosing and monitoring

Dosing:

For all indications except endocarditis: 7mg/kg (Max dose: 560mg) iv OD

For endocarditis (where dosing is synergistic): 3mg/kg (Max dose: 240mg) iv OD

Monitoring:

For patients with Complicated Appendicitis: Gentamicin levels to be taken just before the Third dose (i.e. a trough level).
For other patients (excluding endocarditis): Gentamicin levels to be taken just before the Second dose (i.e. a trough level).
Aim for trough gentamicin level of less than 1mg/L.
If the renal function is normal, give the dose before the trough level is available.
If there is renal impairment see table below.
If previous high levels, hold dose until trough level is known.
Renal function must be checked regularly.

Pre-dose gentamicin level

Interpretation/Action

Less than 1 mg/L

Satisfactory. Continue with same daily dose.
Measure level every 3 days if renal function stable.
If renal function impaired, levels must be done daily.

1-2 mg/L

Wait for level of less than 1mg/L before re-dosing (check every 6 hours).
Increase the dosing interval by 12 hours.
Measure trough level before every subsequent dose and hold until level is known

More than 2 mg/L

STOP gentamicin, and monitor gentamicin level every 12 hours without giving further doses (“trough and hold”) because this implies significant drug accumulation.
Once level is below 1mg/L, Re-dose and consider increasing the dosing interval by 12-24 hours after discussion with named consultant/pharmacist.
Measure trough level before every subsequent dose and hold until level is known.

Step 3b. Patient 1 month and over with eGFR 90ml/min/1.73m²or less - Dosing and monitoring

For all indications except endocarditis:

Initial dose:

Renal function	Dose
eGFR 50-90 ml/min/1.73 m²	7mg/kg once only (max 560mg)
eGFR 20-50 ml/min/1.73 m²	5mg/kg once only (max 400mg)
eGFR under 20 ml/min/1.73 m²	2.5mg/kg once only (max 200mg)
Dialysis	Discuss with named consultant

Aim for trough level of less than 1mg/L
Take a level at 24 hours and wait for the result. Do NOT give the next dose until the result is back
Continue gentamicin when level is less than 1mg/L
If patient has dialysis discuss with named consultant
Renal function must be checked regularly.

Pre-dose gentamicin level	Interpretation/Action
Less than 1 mg/L	Satisfactory. Continue with same daily dose. Measure level before next dose and wait for the result. For eGFR 20-90 ml/min/1.73m², if the second level is under 1mg/L, recheck level twice weekly subsequently.
1-2 mg/L	Wait for level of less than 1mg/L before re-dosing (check every 6 hours). Increase the dosing interval by 12 hours. Measure trough level before every subsequent dose and hold until level is known
More than 2 mg/L	STOP gentamicin, and monitor gentamicin level every 12 hours without giving further doses (“trough and hold”) because this implies significant drug accumulation. Once level is below 1mg/L, Re-dose and consider increasing the dosing interval by 12-24 hours after discussion with named consultant/pharmacist. Measure trough level before every subsequent dose and hold until level is known.

For endocarditis (where dosing is synergistic): speak to paediatric ID.

General Information

Gentamicin IV Treatment

Monitoring and maintenance doses

Editorial Information