Purpose: The results of a study to identify factors associated with serum gentamicin levels outside the therapeutic range in a neonatal population are reported.
Methods: A single-center retrospective chart review was conducted to identify cases involving gentamicin use in the neonatal intensive care unit; a sample of cases sufficient for risk-factor analysis (n = 225) was selected for evaluation. In all evaluated cases, gentamicin was administered according to a standardized dosing protocol based on gestational age and weight. Selected clinical factors and laboratory values potentially associated with undesirably high or low serum drug levels were analyzed.
Results: Of the 225 patient cases included in the analysis, 184 (82%) involved appropriate (i.e., per protocol) gentamicin dosing. Of the 41 doses classified as inappropriate, 33 were higher and 8 were lower than those recommended by the protocol. Six (18%) of the newborns who received doses classified as inappropriately high had supratherapeutic serum trough concentrations, and 3 (9%) had subtherapeutic trough values. Among the neonates with supratherapeutic peak values, none had an elevated trough value and only 1 received a gentamicin dose deemed to be inappropriately high. Factors associated with an increased relative risk (RR) of a supratherapeutic trough included inappropriate dosing (RR, 2.9; 95% confidence interval [CI], 1.18-6.9), an elevated serum creatinine (SCr) concentration (>0.8 mg/dL) on the day of blood sampling for drug level assessment (RR, 25.6; 95% CI, 9.1-71.4), low urine output (<1 mL/kg/hr) on the day of blood sampling (RR, 7.8; 95% CI, 3.0-15.4), and shock (RR, 3.16; 95% CI, 1.32-7.57).
Conclusion: When adhering to a weight-based gentamicin dosing protocol, the SCr level and urine output are the best indicators for identifying neonatal patients at risk for supratherapeutic gentamicin trough levels. Shock and inappropriate dosing strategies also put patients at increased risk for supratherapeutic troughs.