Extended Interval Gentamicin Dosing in Preterm Neonates Less than 35 Weeks Corrected Gestational Age
CPS ePoster Library. Narvey M. Jun 25, 2015; 99147; 84
Michael Narvey
Michael Narvey
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Objective: To confirm that gentamicin 5 mg/kg/dose every 48 hours in neonates less than 35 weeks corrected gestational age (CGA) results in gentamicin serum trough levels within the range of 0.5 – 2 mg/L and peak levels within the range of 6 – 12 mg/L.
Design: Prospective pharmacokinetic (PK) analysis.
Setting: Two neonatal intensive care units and one intermediate care unit in two tertiary care centres.
Patients: Neonates less than 35 weeks CGA who received empiric gentamicin for sepsis between March 10 and June 10, 2014 in whom at least one gentamicin serum level was measured.
Methods: PK analysis was performed following implementation of empiric dosing for gentamicin of 5 mg/kg every 48 h in neonates < 35 weeks CGA (n=54). Target peak and trough serum concentrations post-dose were 6 – 12 mg/L & 0.5 – 2 mg/L at 1 h & 48 h respectively. Serum sampling was recommended at approximately 1, 24, and 48 h after the dose. Between 1 and 3 serum concentration observations were drawn per treatment course. Data were analyzed using a population pharmacokinetic (PK) nonparametric adaptive grid program, Pmetrics 2009-14 Rstudio, Inc. The PK parameters of gentamicin clearance (CL), half-life (t1/2), volume of distribution (Vd), and serum levels were examined for correlations with birth weight, gender, CGA, and postnatal age (PNA).
Results: Mean (confidence interval (CI)) CL and Vd were 43 mL/kg/h (95% CI 39-46), and 0.58 L/kg (95% CI 0.56-0.60), respectively, while the median t1/2 (interquartile range (IQR)) was 9.8 h (IQR 9.3-10.6) (n=54). A one-compartment pharmacokinetic model best represented the data. Mean gentamicin CL at 24 h post-dose was significantly lower in neonates < 14 days PNA (38 mL/kg/h (95% CI 37-39) vs. 55 mL/kg/h (95% CI 40-60) p=0.01). Vd was not influenced by any of the studied covariates. Calculated peak levels achieved therapeutic targets with a mean of 8.2 mg/L (95% CI 7.8-8.6) (n=44); there was no significant difference between peak serum levels when broken down by any covariate. Neonates < 14 days PNA had significantly higher calculated mean gentamicin levels at 24 h post-dose (1.7 mg/L (95% CI 1.6-1.8) vs. 1.1 mg/L (95% CI 0.7-1.6) p=0.0016) and at 48 h post-dose (0.3 mg/L (95% CI 0.3-0.4) vs. 0.2 mg/L (95% CI 0.1-0.3) p=0.027).
Conclusions: Gentamicin 5 mg/kg every 48 h resulted in serum peak levels of 6 – 12 mg/L in 98% of cases compared to a predicted 5% of cases with once-daily doses of 2.5 or 3 mg/kg. Gentamicin doses of 5 mg/kg every 48 h resulted in serum trough levels less than 0.5 mg/L 82% of the time (48 h post-dose) compared to a predicted 9% with once-daily doses (24 h post-dose). Increased clearance with advanced PNA suggests the need for more frequent dosing in premature neonates > 14 days of age.
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