OBJECTIVE To evaluate the ability of a neonatal aminoglycoside dosing nomogram to produce peak serum concentrations greater than 6 mg/L and trough serum concentrations less than 1.5 mg/L.

METHODS Neonates admitted to the Intensive Care Unit who received gentamicin or tobramycin were included if they met the following dosing criteria: Patients < 28 weeks postconceptional age (PCA) received 2.5 mg/kg every 24 hours, those 28–34 weeks PCA received 2.5 mg/kg every 16 hours, and neonates ≥ 35 weeks PCA received 2.5 mg/kg every 12 hours. Serum gentamicin or tobramycin concentrations were obtained and mean patient pharmacokinetic values from this group were used to predict concentrations that would have resulted if the following dosing strategy were used: 4 mg/kg every 36 hours in patients < 29 weeks PCA and 3.5 mg/kg every 24 hours in those ≥ 29 weeks. These doses were then prospectively evaluated in a separate group of neonates.

RESULTS Two-hundred sixty one peak serum concentrations were obtained in patients receiving the initial dosing strategy and 114 neonates received the revised dosing regimen. There were significantly more peak serum concentrations below 6 mg/L in the initial regimen (43%) compared to the new dosing strategy (7.8%). There was also a difference between the percentage of trough serum concentrations > 1.5 mg/L using the initial strategy (33%) compared to the new one (1.8%).

CONCLUSION The new dosing strategy significantly reduced the number of aminoglycoside serum concentrations outside our target reference range; hence, these doses have become the standard of care in our NICU.

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