There are no reliable predictors of gentamicin (G) levels in premature infants. As G is excreted by the kidneys, we hypothesized G levels can be predicted by urine output. We conducted a retrospective study of neonates(gestational age (GA)=30-36wks, n=18) who received G therapy (3 mg/kg/day). Infants with a diagnosis of acute tubular necrosis, asphyxia, hypotension or who received vasopressor support or indomethacin were excluded. We collected data on GA, body weight, urine output (UOP, cc/m2/hr), fluid intake and output(I/O), G intervals/route, body surface area, G levels and day of life G levels drawn. Data were analyzed by student's test, chi square test, correlation coefficient as appropriate. Results showed urine output ≥2 and ≤4.0 cc/k/hr predicted therapeutic G levels (peak= 5-10 mcg/mL) in premature infants (sensitivity 0.69, specificity 1 and positive predictive value 1). Urine output >4 cc/k/hr resulted in levels < 5 mcg/mL. There were significant inverse correlations between peak G levels and UOP (Fig 1) and balance of I/O (Fig 2). We conclude that urine output, 24hrs prior to G level measurement, is a non-invasive, highly predictive parameter of adequacy of dose. We also conclude that the inverse correlation of peak G levels with urine output reflects the change in volume of distribution (balance of I/O).

figure 1

Fig 1

figure 2

Fig 2