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Infection

Is amikacin and gentamicin prescribing appropriate?

The work described here was presented at the UKCPA Virtual Conference Poster Day 2021

The therapeutic drug monitoring (TDM) guideline at Cambridge University Hospital recommends specific dosing and levels for amikacin and gentamicin to minimise ototoxicity and nephrotoxicity. Aminoglycoside doses are based on weight, renal function, age and trough / peak levels. 

Two previous audits evaluated adherence to this guideline; however, additional information could have been included to further access adherence. The hospital’s aminoglycoside TDM guideline was modified in August 2019, whereby it recommended actual body weight should be used with ideal body weight only being used for obese patients. The maximum recommended gentamicin dose was reduced to 480mg and patients above 80 years old should only receive 3mg/kg (1). The use of aminoglycosides has also increased since the recommendation of gentamicin for upper urinary tract infection (UTI) (2). 

This study aimed to evaluate adherence to the updated aminoglycoside TDM guideline. The audit standards were:

  • 100% of patients received an appropriate dose of aminoglycoside based on their weight, age, creatinine clearance and trough/peak levels
  • 100% of patients were prescribed aminoglycosides for an indication approved by the guideline
  • 100% of TDM levels were taken at appropriate times
  • 100% of prescribers followed guideline advice on how to action out-of-range levels.

Data from 162 patients who received aminoglycosides in September 2019 was obtained retrospectively from the electronic health record. Appropriateness of dosing was assessed according to weight, renal function, age and TDM. Aminoglycoside use in paediatrics, patients with cystic fibrosis, surgical prophylaxis, trial without catheter and non-intravenous administration were excluded. 

The lack of awareness of actual body weight, age-based and renal-based dosing were the three most common reasons for dosing error

150 patients received gentamicin and 12 patients received amikacin. The most common indication for gentamicin and amikacin is upper UTI and neutropenic sepsis respectively. Around two-thirds (108/162) of patients received appropriate aminoglycoside doses and 80 percent (20/25) had trough levels taken at appropriate times; an improvement on previous audits. 

The lack of awareness of actual body weight, age-based and renal-based dosing were the three most common reasons for dosing error. Five out of six patients with out-of-range TDM levels were managed appropriately. Although all but one of 162 patients received aminoglycoside for an appropriate indication, poor documentation of the aminoglycoside indication was noted in 94 patients. These patients received gentamicin for UTI; however, there was no clear documentation on whether this was upper or lower UTI. As there are different recommended treatments for upper and lower UTI, there is a possibility that patients with lower UTI received aminoglycosides and thus, the reliability of this result cannot be determined.  

Aminoglycoside prescribing and monitoring is improving. There is a need to increase awareness of weight-, age- and renal-based dosing and to improve documentation of the indication, particularly for UTI. 

References

  • Santos R, Aliyu S, Nickerson E. Prescribing and monitoring of gentamicin, amikacin, vancomycin and teicoplanin. Cambridge University Hospital NHS Foundation Trust; 2019 
  • Aliyu S, Santos R, Micallef C. Urinary and Genital Tract Infections. Cambridge University Hospitals NHS Foundation Trust; 2019. 

The opinions expressed in this article are those of the author. They do not purport to reflect the opinions or views of the UKCPA or its members. We encourage readers to follow links and references to primary research papers and guidance.

Competing interest statement: 

The author declares: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

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