Impact of Postnatal Changes in Creatinine Levels on Plasma Gentamicin Concentrations in Neonates

Gentamicin (GM), a renally eliminated drug, is widely used to treat infections in neonates. Neonatal dosing is typically based on body weight and postmenstrual age (PMA). Although serum creatinine (Cr) is the gold standard for evaluating renal function, Cr at birth may reflect both neonatal and maternal levels. This study aimed to identify determinants of trough GM concentrations, focusing on renal function parameters.

This retrospective, single-center, observational study included 78 neonates who started intravenous GM on postnatal days 0-1. Dosing regimen was stratified by birth weight: < 1200 g (n = 22), 5 mg/kg every 48 h; 1200-1999 g (n = 10), 4 mg/kg every 36 h; ≥ 2000 g (n = 46), 4 mg/kg every 24 h. Dose-normalized trough concentration (C/D) was calculated by dividing trough GM concentration by 24-h equivalent GM dose. Cr level measured at birth (Cr_birth) and the first Cr level measured after GM initiation (Cr_GM) were analyzed.

In neonates < 1200 g and 1200-1999 g, Cr_GM was significantly higher than Cr_birth. C/D correlated significantly with PMA, Cr_GM, and urine output, but not with Cr_birth. Multiple regression analysis incorporating variables measured at birth (Cr_birth and PMA) as covariates identified PMA as the only significant predictor of C/D. When variables available following GM initiation (Cr_birth, PMA, Cr_GM, urine output, and ibuprofen co-administration) were included as covariates, Cr_birth emerged as the sole independent factor predicting C/D.

PMA-based dosing appears to be preferable for determining initial GM dosing on postnatal day 0, whereas Cr-based renal function parameters may be more effective for guiding maintenance dosing.