Prediction of gentamicin peak and trough concentrations from six extended-interval dosing protocols for neonates

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.

Impact of clinical decision support guidelines on therapeutic drug monitoring of gentamicin in newborns

BACKGROUND

Our institution's gentamicin dosing and therapeutic drug monitoring (TDM) practices for newborns were suspected to be very heterogeneous. Once-daily dosing (ODD) or extended-interval dosing (EID) and trough concentration measurement were recommended. Clinical decision support guidelines were developed and implemented as clinical decision support in the computerized prescriber order entry system. Impact on dosing, TDM practices, and blood sampling were evaluated.

METHODS

A 1-year retrospective historically controlled study before (April 2008-March 2009) and after the implementation of guidelines (January 2010-December 2010) for newborns (<30 days of life) receiving gentamicin. Blood concentrations (% of peak concentrations sampled, % of patients with zero or one concentration sampled, % of trough concentrations ≤1 mg/L) and dose regimen (ODD/EID) were compared between groups. Factors potentially associated with gentamicin concentration were analyzed (multivariate analysis).

RESULTS

One hundred thirty-two (postguidelines) versus 102 (preguidelines) patients were included (median gestational age: 34.3 versus 35.8 weeks, P > 0.05). After implementation of the guidelines, an ODD/EID regimen was almost exclusively used (97.7% versus 61.6%, P < 0.001), the percentage of peak concentrations (0.9% versus 17.2%, P < 0.001) and the number of blood samples per patient (87.1% having 0 or 1 concentration measured versus 48.0, P < 0.001) sharply reduced. A significantly higher percentage of trough concentrations were ≤1 mg/L (68.5% versus 33.0%, P < 0.001). The probability of a trough concentration ≤1 mg/L increased with an ODD/EID regimen (odds ratio, 7.23; 95% confidence interval: 3.48-15.0, P < 0.001) and in the postguidelines group (odds ratio, 2.02; 95% confidence interval: 1.01-4.02, P = 0.045).

CONCLUSIONS

Guideline implementation generated a sharp reduction in blood sampling. Clinical benefits of better gentamicin dosing and TDM practices were evident. Cost-effectiveness and clinical benefit of reduced blood sampling should be evaluated.

Use of 4-mg/kg/24-hour empiric aminoglycoside dosing in preoperative neonates with congenital heart disease

BACKGROUND

Empiric dosing of gentamicin has not been evaluated in critically ill neonates with unrepaired congenital heart disease (CHD). Many factors may alter gentamicin pharmacokinetics in this patient population and there are few data describing gentamicin dosing regimens in this patient population.

OBJECTIVE

To determine whether an empiric gentamicin dosing regimen for neonates achieves acceptable serum trough concentrations in neonatal patients with unrepaired CHD receiving alprostadil.

METHODS

Term neonates with unrepaired CHD who received gentamicin for empiric treatment of sepsis were identified over a 3-year period. Patients were included if they received gentamicin 4 mg/kg/dose every 24 hours, were receiving alprostadil for maintenance of a patent ductus arteriosus, and had at least one gentamicin serum trough concentration determined. Patients were evaluated to determine whether they achieved a serum trough concentration of <1 mg/L, and differences in patient characteristics were noted for those who achieved an appropriate trough concentration and those who did not.

RESULTS

Twenty-eight patients met study criteria, and 22% of patients had a trough gentamicin concentration of <1 mg/L at a mean (SD) time of 23.6 (0.3) hours after a dose. Few statistically significant differences in patient characteristics were noted for those who achieved an appropriate serum trough concentration and those who did not, and included Apgar scores at 1 minute and later day of life at admission.

CONCLUSIONS

Current empiric gentamicin dosing regimens may not be appropriate for critically ill neonates with unrepaired CHD. Routine serum concentration monitoring may be warranted in this population.

Comparative evaluation of six extended-interval gentamicin dosing regimens in premature and full-term neonates

PURPOSE

Six extended-interval gentamicin dosing regimens were comparatively evaluated in premature and full-term neonates.

METHODS

Data regarding six physician-ordered dosing regimens of gentamicin for neonates in a hospital neonatal intensive care unit were collected and analyzed. Neonates of gestational age (GA) 29 weeks or younger received 4.5 mg/kg every 48 hours. Neonates of GA 30-34 weeks received one of three dosing regimens: 3.5, 4, or 4.5 mg/kg every 36 hours. Neonates of GA 35 weeks or older received either 3.5 or 4 mg/kg every 24 hours. Blood samples were collected 30 minutes before and 30 minutes after the third dose was infused for binary trough and peak level determinations, respectively.

RESULTS

Peak gentamicin concentrations in the target range were attained most often in neonates of GA 29 weeks or younger who received gentamicin 4.5 mg/kg every 48 hours, in neonates of GA 30-34 weeks treated with gentamicin 3.5 mg/kg every 36 hours, and in neonates of GA 35 weeks or older treated with gentamicin 3.5 mg/kg every 24 hours.

CONCLUSION

For neonates of GA 30-34 weeks, gentamicin 3.5 mg/kg every 36 hours resulted in the highest percentage of peaks in the target range compared with 4 and 4.5 mg/kg every 36 hours. For neonates of GA 35 weeks or older, gentamicin 3.5 mg/kg every 24 hours provided the highest percentage of peaks in the target range compared with 4 mg/kg every 24 hours. The differences between the percentages of trough values in the target range of 0.5-2 μg/mL were not significant among dosing subgroups within each age group.

Accuracy of Empiric Gentamicin Dosing Guidelines in Neonates

OBJECTIVE

To evaluate the accuracy of a neonatal gentamicin nomogram to achieve therapeutic gentamicin serum concentrations without further adjustment, allowing for decreased serum drug monitoring

METHODS

Retrospective single center review of all gentamicin pharmacokinetic evaluations in patients ≤ 30 days of life from July 2005 – June 2007. Patients were evaluated for postnatal age, gestational age, weight, serum creatinine, dose/interval, serum drug peaks and troughs, results of discharge hearing test and recent use of indomethacin. Logistic regression was utilized to determine potential factors impacting overall dosing accuracy, potentially allowing for decreased therapeutic drug monitoring. Factors found to be significant were incorporated into new guidelines which were evaluated through pharmacokinetic modeling.

RESULTS

Overall accuracy rate was 84% when empiric dosing guidelines were utilized; 16% of all doses were changed due to supratherapeutic troughs and 1% were changed due to subtherapeutic peaks. Variables found to impact the necessity for dose changes incuded gestational age (p≤0.001), weight (p≤0.001), indomethacin use (p≤0.001), number of indomethacin doses used (p≤0.001 and p=0.009 for 1–3 and 4–6 doses, respectively), and SCr in patients ≥ 7 days old (p=0.028); however, only gestational age remained a significant predictor when all other factors were considered (p=0.008). The current guidelines were changed to account for increased troughs in patients ≤ 28 weeks gestation and examined through pharmacokinetic modeling. Pharmacokinetic modeling of the new guidelines predicted an overall accuracy of 94%.

CONCLUSIONS

From the data gathered regarding the accuracy in patients ≥ 35 weeks gestation, we recommend to decrease therapeutic drug monitoring within this cohort. Utilizing the results of regression analysis, the current guidelines have been adjusted to allow for increased clearance in patients ≤ 28 weeks gestation, although they still need to be prospectively evaluated.

Two nomograms for determining extended-dosing intervals for gentamicin in neonates

PURPOSE

The development of two nomograms to predict dosing intervals for gentamicin in neonates based on one gentamicin concentration is described.

METHODS

Pooled data from three retrospective studies on neonates age seven days or younger were used to create nomograms that would predict dosing intervals for gentamicin. The population volume of distribution (0.45 L/kg) and a determined half-life were used to create nomogram cutoff concentrations that could select a dosing interval for neonates to achieve steady-state trough concentrations of < or =0.5 or < or =1 mg/L. A dose of 4 mg/kg was used to simulate concentration-versus-time profiles for included neonates based on their individual pharmacokinetic data. Predicted concentrations from hours 6 to 22, at one-hour intervals, for each neonate were compared against the nomograms and evaluated for the number of correct interval predictions. The nomograms were considered to have failed at any time point where they indicated an interval that would not have achieved the desired trough concentration of < or =0.5 or < or =1 mg/L or if the interval chosen was longer than necessary.

RESULTS

The 0.5- and 1-mg/L nomograms predicted correct dosing intervals for 81-92% of neonates for postinfusion hours between 15 to 21 and 86-93% for postinfusion hours of 13 and 21, respectively. Accuracy of the nomograms to predict correct dosing intervals improved as the postinfusion time before the next concentration measurement increased.

CONCLUSION

Using the two nomograms may help predict the correct extended-dosing intervals of gentamicin administration for neonates. Prospective evaluation and validation of the nomograms may be necessary for their wider use as a clinical tool.