Principles of gentamicin use for surgical antibiotic prophylaxis

The Gram-negative spectrum of cefazolin is adequate for most surgical procedures for which Gram-negative activity is required. However, gentamicin continues to be recommended as prophylaxis for the few procedures requiring a broader spectrum of Gram-negative activity. Gentamicin is also used as an alternative when cefazolin is contraindicated.

The risk of gentamicin toxicity is very low when it is given as a single dose for prophylaxis; there are few absolute contraindications to its use. Contraindications and precautions to gentamicin for surgical prophylaxis are listed in Contraindications and precautions to gentamicin for surgical prophylaxis.

Figure 1. Contraindications and precautions to gentamicin for surgical prophylaxis

Contraindications

Do not use gentamicin for surgical prophylaxis in patients with:

  • a history of aminoglycoside-induced vestibular or auditory toxicity
  • a history of a severe hypersensitivity reaction to an aminoglycoside (these reactions are rare) [NB1]
  • chronically impaired kidney function (adults with a creatinine clearance [CrCl] less than 20 mL/minute) [NB2] [NB3].

Precautions

Gentamicin should generally not be used for surgical prophylaxis in patients:

  • with pre-existing significant auditory impairment
  • with a pre-existing vestibular condition
  • who have a first-degree relative with aminoglycoside-induced auditory toxicity, since some people have a rare inherited genetic predisposition [NB4]
  • who have a condition or who are taking drugs that can interfere with neuromuscular transmission [NB5]
  • with rapidly deteriorating kidney function.

A single dose of gentamicin can be used for surgical prophylaxis in patients who are frail and elderly (eg 80 years or older).

Note:

NB1: Severe hypersensitivity reactions include anaphylaxis, compromised airway, angioedema, hypotension, collapse, severe cutaneous adverse drug reactions (eg drug rash with eosinophilia and systemic symptoms [DRESS], Stevens–Johnson syndrome / toxic epidermal necrolysis [SJS/TEN]), and significant internal organ involvement (eg acute interstitial nephritis).

NB2: Do not avoid gentamicin in patients with minimal residual kidney function receiving long-term dialysis.

NB3: For gentamicin use in children with kidney impairment, seek expert advice.

NB4: Ask about a family history of hearing loss before administering gentamicin. Aminoglycoside-induced ototoxicity has a genetic susceptibility in some individuals. Mitochondrial mutations have been identified as genetic factors underlying hearing loss in cases of aminoglycoside-induced ototoxicity. These mutations are also associated with a predisposition to isolated hearing loss. Where possible, genetic testing for these mutations should be considered in patients with a family history of aminoglycoside-induced ototoxicity.

NB5: Gentamicin can exacerbate myasthenic symptoms in patients with myasthenia gravis.

There is divergent practice in gentamicin dosing for surgical prophylaxis; doses from 1.5 to 5 mg/kg are used. The doses recommended in these guidelines are based on extensive clinical experience and the pharmacokinetic/pharmacodynamic properties of gentamicin.

The appropriate dose of gentamicin depends on the duration of prophylaxis required.

  • When a short duration (up to 6 hours) of prophylaxis is required, use 2 mg/kg (actual body weight) up to 180 mg.
  • If there is a moderate likelihood that a procedure will continue for longer than 6 hours, consider using the dose below.
  • When a longer duration (up to 24 hours) of prophylaxis is required (eg some cardiac procedures), the dose depends on the patient’s kidney function:
    • For adults with a CrCl of 40 mL/min or more, or children with normal kidney function, use 5 mg/kg (actual body weight) up to 480 mg.
    • For adults with a CrCl of 20 to 39 mL/min, use 4 mg/kg (actual body weight) up to 380 mg.

Do not use gentamicin for surgical prophylaxis in adults with a CrCl less than 20 mL/min; seek expert advice. For gentamicin use in children with kidney impairment, seek expert advice.

For patients with obesity (eg adults with a body mass index of 30 kg/m2 or more), use adjusted body weight (see ../Aminoglycoside-use-in-special-patient-groups/c_ABG_Aminoglycoside-use-in-special-patient-groups_topic_5.html#c_ABG_Aminoglycoside-use-in-special-patient-groups_topic_5__fig-504) to calculate the gentamicin dose.

When gentamicin is used for surgical antibiotic prophylaxis, monitoring is not required.