Audience

• HHSCP only
• Paediatrics only

For use in renal impairment, meningitis, endocarditis and burns

Indication

• Gentamicin is an aminoglycoside antibiotic with a broad spectrum of activity against some Gram-positive bacteria, many Gram-negative bacteria including Pseudomonas aeruginosa.
• Generally used as the first line aminoglycoside, except in cystic fibrosis.
• For obese patients (actual body weight >120% of the ideal body weight), use ideal body weight to calculate gentamicin doses.  Extrapolate estimated IBW from the height centiles on the growth chart.

Therapeutic drug monitoring 

• Monitor blood levels BEFORE and AFTER 3rd dose (and 3rd dose following a dosage adjustment).
• If levels satisfactory repeat after 3 to 4 days, unless clinically indicated. See note below on duration of treatment.
• Monitor earlier and more frequently if renal function is unstable. This may be before every dose to ensure trough levels have fallen prior to the next dose.
• Sample trough level immediately prior to dose and peak level one-hour post dose.

Therapeutic range:

• Trough: <2mg/L (<1mg/L for endocarditis, <2mg/L for cystic fibrosis)
• Peak: 5 to 10mg/L (3 to 5mg/L for endocarditis, 8 to 12mg/L for cystic fibrosis)
• If levels unsatisfactory seek advice from the Clinical Pharmacist or microbiology on dose or interval adjustment and re-sample at the next dose.
• In renal impairment give an initial dose of 2·5mg/kg (1 month to 11 years) or 2mg/kg (12 to 17 years), then take a trough level before the next dose is due, and only re-dose when trough <2mg/L. Subsequent doses should be based on serum gentamicin concentration and renal function to avoid accumulation of the drug.

For patients on renal replacement therapy, then seek further advice from RHSC, Glasgow.

Supply

• 20mg in 2mL or 80mg in 2mL vials/ampoules.

Preparation

• Give by intramuscular injection or as a slow IV bolus over 3 to 5 minutes.
• Ensure adequate flushing if patient is also prescribed a penicillin or cephalosporin.

Compatibilities / incompatibilities

• See Medusa NHS Injectable Medicines Guide.

Monitoring / Side effects

Renal function

• Prescribers should assess prior to prescribing, and check child is passing urine. See Think Kidneys guidance.
• Nephrotoxicity may be compounded by other agents, eg, amphotericin, cephalosporins, ciclosporin, indometacin, tacrolimus, vancomycin.

Auditory and vestibular function

• Prescribers should monitor for signs of ototoxicity and refer to audiology if it develops, or if gentamicin is continued for more than 7 days.
• Signs of ototoxicity include new tinnitus, dizziness, poor balance, hearing loss or oscillating vision.
• Stop gentamicin if ototoxicity occurs, and refer to microbiology or an infection specialist for advice on future therapy.
• Ototoxicity may be compounded by, eg, furosemide, and vancomycin. Monitor renal function & fluid balance closely.

NOTES

• Review the need for continuing treatment beyond 72 hours with a consultant microbiologist.

Contra-indications

• Contra-indicated in patients with Myasthenia Gravis.
• Hypersensitivity to gentamicin or other ingredients.

Interactions

• Enhances the effects of non-depolarising muscle relaxants eg atracurium.

Licensed status

• Licensed.