Reevaluation of Gentamicin Dosing in the Neonatal Population

Abstract

Objective:

To determine whether current recommendations for gentamicin dosing in full-term newborns yield a serum peak concentration of 6–7 μg/mL and a trough concentration less than 2 μg/mL in treating suspected neonatal sepsis.

Design:

Two-year retrospective chart review.

Setting:

Community hospital.

Results:

Sample consisted of 175 newborns with a gestational age ranging from 36 to 43 weeks and 188 sets of concentrations. Pharmacokinetic parameters were calculated using a one-compartment, first-order elimination model and were reported as follows: volume of distribution 0.59 kg/L, elimination rate constant (k_e) 0.11 h⁻¹ (half-life [t_1/2] 6.8 h) at 36–37 weeks of age, with a significant change (p < 0.05) in rate constant occurring at 38–43 weeks of life, and k_e 0.12 h⁻¹ (t_1/2 6.0 h) when using a two-tailed, two-sample t-test. Extrapolated mean peak concentrations were 5.8 ± 1.2 μg/mL and trough concentrations were 1.5 ± 0.5 μg/mL. Furthermore, 14% of newborns had an extrapolated trough concentration of 2.0 μg/mL or more.

Conclusions:

The current 2.5-mg/kg dosage is appropriate for the neonatal population studied. However, to decrease the number of potentially toxic trough concentrations, the initial dosing interval should be extended to every 18 hours for full-term neonates (>37 weeks gestation) with normal kidney function and for neonates with a gestational age of 36–37 weeks.