Performance of a dosage individualization table for extended interval gentamicin in neonates beyond the first week of life

Individualization of treatment with gentamicin in neonates based on drug concentration in the blood serum

OBJECTIVE

Aim: To evaluate how useful it is to make measurements of gentamicin concentrations in newborns' blood in order to optimize antibiotic therapy.

PATIENTS AND METHODS

Material and methods: 73 newborns empirically treated with gentamicin, in doses consistent with the Neofax® guidelines. There were 152 measurements of maximum and minimum serum gentamicin concentrations. Samples were determined based on the chemiluminescence technique on the Siemens Advia Centaur analyzer. The concentrations of gentamicin that were measured were compared with various therapeutic ranges used in the literature.

RESULTS

Results: According to the standards adopted in the University Hospital in Wrocław, the maximum concentration was reached in 38.16% of all the children, while the minimum in 26.32%. In other children the concentrations were below or above the therapeutic range. According to the Neofax® guidelines, the intended maximum concentration was observed in 71.05% of the newborns, and the minimum in 32.89%. The minimum concentration of <2 mg/L was found in 93.42% of the newborns, while >2 mg/L was determined in 33.33%, despite a 48-hour dosing interval. These were premature babies (<28th week of gestational age) and 55.56% of them reached a maximum concentration of 5-12 mg/L. There was no significant correlation between maximum or minimum concentration and gestational age or body weight.

CONCLUSION

Conclusions: 1. The dosage of gentamicin in newborns according to the Neofax® recommendations does not ensure achieving the intended serum antibiotic concentrations. 2. In order to optimize gentamicin therapy in newborns it is necessary to individualize the dose based on measurements of drug concentrations in the blood and pharmacokinetic calculations.

Extended-interval Dosing of Gentamicin in Premature Neonates Born at <32 Weeks' Gestation and >7 Days of age

PURPOSE

Extended-interval dosing (EID) regimens of gentamicin have been validated for treating confirmed or suspected early- and late-onset sepsis in preterm infants in the first week of life. Despite the marked changes in volume of distribution and renal clearance in preterm infants after the first few days of life, few studies have validated EID regimens of gentamicin in this population. The objective of the study was to evaluate an EID regimen of gentamicin in infants born at <32 weeks' gestational age and aged >7 days.

METHODS

This observational study of an EID regimen was conducted in 39 infants. Dosing interval was based on the serum drug concentration at 22 hours after the administration of the first dose of 5 mg/kg. Gentamicin peak (5-12 µg/mL) and trough (<2 µg/mL) levels were compared to those in a historical control group of 39 infants who received traditional-interval dosing (TID) of 2.5 mg/kg of gentamicin with dosing intervals of 8, 12, or 24 hours.

FINDINGS

There were no differences in birthweight, gestational age at birth, postmenstrual age, weight at the start of gentamicin administration, postnatal age, small for gestational age status, antenatal corticosteroid use, or postnatal indomethacin exposure between the 2 groups. In the EID group, dosing intervals were 24 hours in 30 infants, 36 hours in 6 infants, and 48 hours in 3 infants. Compared with the TID group (n = 39), the EID group had a significantly higher peak level (median, 9.0 vs 4.7 µg/mL) and a significantly lower trough level (median, 0.7 vs 1.1 µg/mL) (both, P < 0.001). On regression analysis, the postmenstrual age was correlated significantly with trough levels in the EID group. There was no adverse effect on renal function in either group. On follow-up, 1 infant in the EID group and 2 infants in the TID group had evidence of sensorineural hearing loss.

IMPLICATIONS

In infants born at <32 weeks' gestation and >7 days of age, an EID gentamicin regimen, with a dosing interval based on a single concentration measurement at 22 hours after the administration of the first dose, achieved therapeutic peak and trough levels and performed significantly better than did a TID regimen in reaching target peak and trough levels. Larger-scale trials are needed for assessing the clinical efficacy (treatment failure/success) of these regimens.

Should gentamicin trough levels be routinely obtained in term neonates?

OBJECTIVE

Gentamicin is a common antibiotic used to treat sepsis in neonates. We hypothesize that obtaining routine gentamicin trough levels may not be necessary in low-risk, term infants.

STUDY DESIGN

We performed a retrospective cohort study of term infants (n=346) treated with gentamicin in a single level III neonatal intensive care unit (NICU). The results of gentamicin trough levels and the correlation with risk factors and potential side effects were recorded. In addition, we conducted a survey of 75 academic NICUs across the United States regarding their gentamicin monitoring practice.

RESULTS

Routine trough levels did not predict potential gentamicin toxicity in neonates with low risk factors. Regression analysis demonstrated a positive correlation between gentamicin trough levels and serum creatinine. The survey of the NICUs in the United States demonstrated significant inconsistency in gentamicin monitoring practice.

CONCLUSION

Obtaining gentamicin trough levels guided by risk factors is more appropriate than obtaining routine trough levels in low-risk term neonates.