To determine the rate of and predictors for guideline-discordant preoperative gentamicin dosing in urologic surgery and to assess the risk of nephrotoxicity in patients who receive the recommended high-dose prophylaxis.

We retrospectively reviewed all adult patients who received preoperative gentamicin for urologic surgery from January 1, 2017 - October 3, 2019. Doses were categorized as guideline-concordant or -discordant using a cutoff of 4.5 mg/kg dosing weight. We used multivariable logistic regression to identify predictors for guideline-discordant dosing. Postoperative kidney injury was assessed using RIFLE criteria.

Among 2134 patients, 89% received a preoperative dose ≤ 4.5 mg/kg. Older age (70+ years) and endoscopic surgery were significant risk factors for guideline-discordant dosing (OR 2.54, P< 0.001; OR 6.21, P<0.001). Among 735 patients with complete data, there was no significant difference in the risk of kidney injury between those who received a dose less than 4.5 mg/kg and those who received a higher dose (OR 0.89, 95% CI: 0.26 – 2.99, P = 0.75).

Preoperative gentamicin is commonly administered at lower than recommended doses for urologic surgery. Older age and endoscopic surgery are significant predictors of guideline-discordant dosing. The risk of kidney injury following high-dose preoperative gentamicin for urologic procedures is likely comparable to the risk at lower doses.