Experience of adopting a standardised nomogram for gentamicin monitoring- an audit

Gentamicin, an aminoglycoside antibiotic, requires therapeutic drug monitoring to decrease the risk of nephrotoxicity and ototoxicity. We audited compliance with our dosing and monitoring guidelines since adoption of the Barnes-Jewish Nomogram for once daily 5mg/kg dosing in September 2018.

We retrospectively reviewed 62 patients who received 171 gentamicin doses with 173 accompanying levels taken between 1/11/18 and 31/1/19.

The audit demonstrated overall poor adherence to guidelines. Only 50% of patients received the correctly calculated dose. 40% of gentamicin levels were taken between 6-14 hours resulting in a large number of uninterpretable levels requiring additional actions e.g. repeat levels. 50% of follow up doses were given in the correct time frame. For patients with normal renal function twice weekly monitoring is recommended. In all cases (n=35) where this applied levels were monitored more frequently that indicated. U&Es were regularly monitored for all patients and we did not identify any acute kidney injury.

The Barnes-Jewish nomogram was adopted to provide a standardised evidence based monitoring system for gentamicin. However our audit demonstrates the guidance was not well executed clinically. There appeared to be a lack of appreciation and responsibility for monitoring and interpretation of levels. This resulted in erratic sampling, unnecessary levels, and delayed doses. As a result of this audit we intend to adopt a simpler trough level system based on the gentamicin SPC. Our audit demonstrates the need to evaluate service improvement implementations since theoretical benefits do not always translate in to clinical practice