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

Therapeutic drug monitoring of antimicrobial drugs in neonates. An opinion paper

PURPOSE

Neonatal infections are associated with high morbidity and mortality rates. Optimal treatment of these infections requires knowledge of neonatal pharmacology and integration of neonatal developmental pharmacokinetics of antimicrobial drugs in the design of dosing regimens for use with different gestational and postnatal ages. Population pharmacokinetic (PK) and pharmacodynamic (PD) models are used to personalize the use of these drugs in these fragile patients. The final step to further minimize variability in an individual patient is therapeutic drug monitoring (TDM), where the same population PK/PD models are used in concert with optimally drawn blood samples to further fine-tune therapy. The purpose of this manuscript is to describe the present status and future role of model-based precision dosing and TDM of antimicrobial drugs in neonates.

METHODS

PubMed was searched for clinical trials or clinical studies of TDM in neonates.

RESULTS

A total of 447 papers were retrieved, of which 19 were concerned with antimicrobial drugs. Two papers (one aminoglycoside and one vancomycin) addressed the effects of TDM in neonates. We found that, in addition to aminoglycosides and vancomycin, TDM also plays a role in beta-lactam antibiotics and antifungal drugs.

CONCLUSION

There is a growing awareness that, in addition to aminoglycosides and vancomycin, the use of beta-lactam antibiotics, such as amoxicillin and meropenem, and other classes of antimicrobial drugs, such as antifungal drugs, may benefit from TDM. However, the added value must be shown. New analytical techniques and software development may greatly support these novel developments.

Extended interval dosing of gentamicin in premature neonates ≤ 28-week gestation

AIM

To evaluate an extended interval dosing (EID) regimen of gentamicin in neonates ≤28-week gestation.

METHODS

In 2008, an EID regimen for gentamicin was introduced for all neonates admitted to the NICU in Calgary. The dosing interval was based on a 22 h level after the first dose of 5mg/kg. We conducted an observational study in 33 infants ≤28-week gestation on the EID regimen from the first day of life and compared gentamicin peak and trough levels with a historical control of 34 infants who received gentamicin in a dose of 2.5 mg/kg every 24 h (TID, traditional interval dosing).

RESULTS

In the EID group, based on the 22 h level, dosing interval was 36 h in 20 neonates and 48 h in 13 neonates. All neonates, except one, achieved therapeutic peak and trough levels. Compared to the TID group, the EID group had higher peak levels (median 9.8 μg/mL vs. 4.6 μg/mL, p < 0.001) with no difference in trough levels. With target peak levels of 5-12 μg/mL and trough levels of <2 μg/mL, a higher proportion of neonates in the TID group would need dose adjustment.

CONCLUSION

In neonates ≤ 28-week gestation, an EID regimen from day one of life, using a single level 22 h after the first dose for dosing interval, achieves therapeutic peak and trough levels and more optimum peak levels as compared to a TID regimen.

Validation of a dosage individualization table for extended-interval gentamicin in neonates

BACKGROUND

Extended-interval aminoglycoside dosing is increasingly used in neonates; however, guidance on how to monitor concentrations and adjust dosages accordingly is limited.

OBJECTIVE

To prospectively validate the use of a 22-hour gentamicin concentration dosing table for the individualization of extended-interval dosing in the neonatal population by examining the peak and trough concentrations achieved through its use.

METHODS

A prospective observational study was carried out on gentamicin concentrations achieved using a 22-hour post-first-dose gentamicin concentration dosing table for determining dosing intervals in neonates. Neonates (N = 104) in the first week of life, gestational age 23 weeks to full term, in level II and III neonatal intensive care units were included. Neonates were given gentamicin 5 mg/kg intravenously; a table using 22-hour post-first-dose gentamicin concentrations was then used to individualize dosing intervals. Pre- and post-serum gentamicin concentrations on the dosing interval indicated were measured with the second or third doses and used to calculate the peak and trough concentrations achieved.

RESULTS

Use of the 22-hour post-first-dose gentamicin concentration dosing table resulted in dosing intervals that provided appropriate peak (mean 10.55 mg/L) and trough (mean 0.75 mg/L) concentrations (with second or third doses) in all neonates. All patients had trough concentrations less than 2 mg/L, and 73% had a trough concentration less than 1 mg/L. No peak concentrations were less than 5 mg/L, 82% of patients had a peak concentration from 5 to 12 mg/L, and the remaining 18% had concentrations from 12.1 to 16 mg/L. Peak and trough concentrations were similar across all gestational ages.

CONCLUSIONS

Use of a 22-hour post-first-dose gentamicin concentration dosing table to individualize extended-interval gentamicin dosages in neonates resulted in appropriate peak and trough concentrations in all neonates studied. Use of this table will result in appropriate extended-interval aminoglycoside dosages in neonates early in treatment, using a single serum concentration.