Gentamicin Prescribing

Gentamicin Prescribing

Jun 6, 2016 1
General medicine,infectious diseases,onthepods

James talks to Dr Kate Clezy about gentamicin prescribing.

Summary Writer:  Bi Yi Chen

Editor:  James Edwards

Interviewee:  Kate Clezy

About Dr Kate Clezy

Kate Clezy is an Infectious Diseases Physician and the Director of Infectious Diseases at the Prince of Wales Hospital. She is consultant to the SESLHD Clinical Governance Unit for Infection Prevention and Control and Clinical Advisor, Healthcare Associated Infections Program, Clinical Excellence Commission.

Gentamicin Prescribing

With Dr Kate Clezy, Infectious Diseases Physician at Prince of Wales Hospital, New South Wales, Australia

Introduction

This podcast aims to cover the basics of gentamicin prescribing.

Case

You are a Junior Doctor working in orthopedics. A 75-year-old female develops urosepsis post-operatively and you are considering prescribing some ampicillin and gentamicin. You have checked that she is not allergic to gentamicin.

  • Whether the patient is taking any other nephrotoxins
  • Past or family history of adverse effects from aminoglycoside use, such as ototoxicity
  • Aminoglycosides are bactericidal antibiotics that inhibit protein synthesis through binding to the 30s subunit of the ribosome of the bacteria. This leads to the incorrect insertion of amino acids into the peptide chain, and if the peptide chain is in the cell membrane, it no longer functions correctly and the cells will not divide properly, ultimately resulting in the death of organism.
  • It is usually given parenterally
  • It can be given intramuscularly
  • It can be nebulised in cystic fibrosis patients with pseudomonas bronchiectasis
  • It can be given orally, for local effects on the gut
  • It works very well against gram negatives organisms and pseudomonas
  • Therefore, gentamicin is good for gut-related conditions and urinary tract-related infections
  • For example, E coli, Proteus, Klebsiella pneumoniae
  • It is important to know the creatinine clearance which can be calculated from the serum creatinine
  • In this case, it would also be important to do blood cultures before commencing the patient on antibiotic therapy
  • The initial dose is 4-7mg/kg of the ideal body weight
  • In patients who are septic, usually a higher dose (7mg/kg) is given due to the altered volume distribution
  • Other groups that require dosing adjustment includes patients on renal placement therapy, and patients with ascites or burns. It would also be advisable in these groups to seek the opinion of a pharmacist
  • Patients with creatinine clearance of less than 40ml/min and over the age of 80 should be dosed with caution, and have their renal function monitored closely
  • The variable dosing section of the medication chart so that the team will regularly review the indication for dosing
  • If it is empirical therapy, as in this case, the patient will usually receive 3 doses (0, 24, 48hrs) or for a maximum of 48 hours. The time of dosing would not matter as you will not have to test the level
  • With directed therapy however, the trough level of gentamicin needs to be monitored. The gentamicin should be charted so that the trough level coincides with the time of routine blood collection
  • Gentamicin provides cover for most of the gram negative bacteria but ampicillin broadens the coverage to gram positive organisms. The two drugs also work synergistically to combat enterococcus
  • Ototoxicity
    • Can present with hearing loss, tinnitus, or vestibular toxicity
    • Affects 1% of patient
    • Rate of complication is unpredictable, but generally more common with cumulative dosing
  • Nephrotoxicity
    • More common with cumulative dosing
    • Causes proximal tubule damage which is reversible if detected early
    • The rate of toxicity is not related to trough level
  • Neuromuscular blockade leading to respiratory depression
  • Familial toxicity secondary to gentamicin use
  • Pre-existing tinnitus, significant hearing loss, or vestibular dysfunction (because it may worsen their pre-existing condition and it is difficult to determine the magnitude of contribution of gentamicin to their adverse effect)
  • Concurrent nephrotoxic drugs
  • Recent anaesthesia
  • Neuromuscular blockades, such as suxamethonium. Gentamicin can potentiate the action of these drugs and enhance neuromuscular blockade
  • Magnesium sulfate -> neuromuscular blockade
  • Nephrotoxins-> additive toxicity to the kidneys
  • Myasthenia Gravis
  • It is rapidly bactericidal
  • There is lower rates of resistance for urinary pathogens
  • It is associated with a low rate of Clostridium difficile
  • Gives a broader cover of urinary organisms, and also covers pseudomonas which ceftriaxone does not
  • Neuromuscular blockades, such as suxamethonium. Gentamicin can potentiate action of these drugs and enhance neuromuscular blockade
  • Magnesium sulfate -> neuromuscular blockade
  • Nephrotoxins-> additive toxicity to the kidneys
  • Myasthenia Gravis
  • Empirical dosing does not require monitoring serum gentamicin level
  • Depends on the condition and dosing schedule
  • Should consult the hospital pharmacist
  • Seek senior advice
  • Gentamicin is an excellent drug for the treatment of gram negative sepsis
  • It needs to be dosed according to the patient’s ideal body weight
  • If patient is dosed for over 48 hours, please ask senior clinician and pharmacist for advice regarding monitoring

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Tags: #aminoglycoside,#ampicillin,#Antibiotics,#bactericidal antibiotics,#creatinine clearance,#gentamicin,#gentamicin prescribing,#gram negative sepsis,#gram negatives organisms,#Nephrotoxicity,#ototoxicity,#pseudomonas,#serum creatinine

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1 Comment

  1. neha

    July 12, 2019 at 12:55 am

    great podcasts

    Reply

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