Effectiveness of a gentamicin dosing protocol based on postconceptional age: comparison to published neonatal guidelines

Gentamicin dosing in neonates: evaluation of a dosing protocol

A study was carried out to examine the dosing of gentamicin and to investigate some of the determinants of serum gentamicin concentrations in neonates at the Royal Hobart hospital, Tasmania, Australia, and to examine the appropriateness of the current dosing protocol (that of the Royal Children's hospital, Melbourne). Clinical and demographic data were retrospectively collected from the records of 39 neonates who had received therapy with gentamicin for suspected or proven septicaemia during the period May to September, 1993. Peak and trough serum concentrations of gentamicin were measured, at least 36 hours after starting therapy. The mean gestational age (± SD) of the sample was 32.3 ± 4.9 weeks, and 30 patients were male. The mean dosage of gentamicin was 4.0 ± 1.3mg/kg/day and the median duration of therapy was 4 days (range 2 to 22 days). Trough serum concentrations of gentamicin ranged from 0.6 to 6.0mg/L (mean 1.9 ± 1.0mg/L), with 35.9 per cent being 2.0mg/L or higher. Peak serum concentrations ranged from 4.3 to 12.9 mg/L (mean 6.1 ± 1.5 mg/L), with 89.7 per cent being between 5.0 and 8.0mg/L. The peak and trough serum concentrations were significantly related, while the total daily dosage of gentamicin and the resulting peak and trough serum concentrations were not significantly related. The trough serum concentration of gentamicin was significantly related to the serum creatinine concentration. Patients who had been dosed correctly according to the protocol were less likely to have a potentially toxic trough serum concentration of gentamicin. Those administered gentamicin every 12 hours tended to have higher serum trough concentrations of the drug than those who received it either 18- or 24-hourly.

This study has confirmed that excessive serum concentrations of gentamicin occur frequently in neonates, a situation which may be improved by greater usage of an 18-hourly dosing regimen and prompt adjustment of dosage according to renal function.

Characterization of an MPS I-H knock-in mouse that carries a nonsense mutation analogous to the human IDUA-W402X mutation

Here we report the characterization of a knock-in mouse model for the autosomal recessive disorder mucopolysaccharidosis type I-Hurler (MPS I-H), also known as Hurler syndrome. MPS I-H is the most severe form of alpha-l-iduronidase deficiency. alpha-l-iduronidase (encoded by the IDUA gene) is a lysosomal enzyme that participates in the degradation of dermatan sulfate and heparan sulfate. Using gene replacement methodology, a nucleotide change was introduced into the mouse Idua locus that resulted in a nonsense mutation at codon W392. The Idua-W392X mutation is analogous to the human IDUA-W402X mutation commonly found in MPS I-H patients. We found that the phenotype in homozygous Idua-W392X mice closely correlated with the human MPS I-H disease. Homozygous W392X mice showed no detectable alpha-l-iduronidase activity. We observed a defect in GAG degradation as evidenced by an increase in sulfated GAGs excreted in the urine and stored in multiple tissues. Histology and electron microscopy also revealed evidence of GAG storage in all tissues examined. Additional assessment revealed bone abnormalities and altered metabolism within the Idua-W392X mouse. This new mouse will provide an important tool to investigate therapeutic approaches for MPS I-H that cannot be addressed using current MPS I-H animal models.

Vancomycin and gentamicin in neonates: hindsight, current controversies, and forethought

The use of both vancomycin and gentamicin in the treatment of suspected or documented neonatal infections, while routine, is a challenge for bedside and advanced practice nurses caring for neonates in intensive care units. A review of the background information surrounding neonatal infections as well as the history, intended use, and the pharmacokinetic and pharmacodynamic properties of vancomycin and gentamicin is presented with the goal of aiding in proper treatment with these two medications. Specific attention is given to doses in special situations, means of drug monitoring, strategies for avoiding antibiotic resistance, alternative medication choices, and areas for future investigation.

Population pharmacokinetics and relationship between demographic and clinical variables and pharmacokinetics of gentamicin in neonates

Population pharmacokinetic parameter estimates were calculated from 725 routine plasma gentamicin concentrations obtained in 177 neonates of 24 to 42 weeks' gestational age in their first week of life. Kel increases and V/W decreases with increasing gestational age. Almost identical results were obtained with iterative two-stage Bayesian fitting (MW\PHARM 3.30) as with a non-parametric maximization algorithm (NPEM2). The effect of various covariates on drug disposition was investigated retrospectively using multiple regression analysis. Predictive power for Kel increases with rising gestational age. For neonates </=28.5 weeks and neonates >28.5 weeks and </=30.9 weeks, the predictive power of the regression equation for Kel was relatively low (r2 respectively 0.270 and 0.364). Better predictivity was found for Kel at gestational ages >30.9 weeks (r2 = 0.482), with gestational age, postnatal age, and Apgar score at 5 minutes being predictors. A very strong correlation existed between volume of distribution and weight (r2 = 0.83). Volume as a function of weight could be described with low predictivity by gestational age and to a lesser degree by Apgar score at 5 minutes (r2 = 0.298). The developed models need appropriate prospective clinical validation.

Comparison of two gentamicin dosing schedules in very low birth weight infants

BACKGROUND

Several dosing schedules for gentamicin have been recommended for very low birth weight infants during the early neonatal period. We conducted a prospective, randomized, controlled trial to compare efficacy and pharmacokinetics of two dosing schedules in preterm neonates.

METHODS

Fifty-eight very low birth weight infants (600 to 1500 g), prescribed gentamicin for treatment of suspected sepsis during the first week after birth, were randomized to receive either the new dosing schedule [every 48 h (q48h)] or the existing dosing schedule [every 24 h (q24h)]. Infants in the "q48h" group received gentamicin at 5.0 or 4.5 mg/kg/dose q48h depending on weight group and infants in the "q24h" group received 2.5 or 3.0 mg/kg/dose q24h. Peak and trough serum gentamicin concentrations were monitored.

RESULTS

Peak serum gentamicin concentrations after the first dose were significantly higher in the q48h infants than in q24h infants (8.19 +/- 1.3 vs. 6.04 +/- 2.2, P = 0.00001). Ninety percent of all peak serum gentamicin concentrations in the q48h group were in a higher therapeutic range of 6 to 12 microg/ml as compared with 55% of q24h (P = 0.0005). None of the q48h infants had subtherapeutic serum gentamicin concentrations immediately after administration of the first dose as compared with 36% of q24h infants (P < 0.005). Eighteen percent of q24h infants continued to have peak serum gentamicin concentrations in subtherapeutic range even after the third dose at 48 h. Trough serum gentamicin concentrations were significantly lower in q48h infants than in q24h infants. However, 9 of 30 (30%) q48h infants had trough serum gentamicin concentrations of < or = 0.5 microg/ml before the dose at 48 h and 4 of the 9 had serum gentamicin concentrations of <1 microg/ml at 24 h after the first dose.

CONCLUSIONS

The q48h dosing schedule of gentamicin given to very low birth weight infants during the first week after birth achieved therapeutic serum gentamicin concentrations and potentially higher peak to MIC ratios for microorganisms in all infants. However, nearly one-third of the infants had extremely low serum gentamicin concentrations before the next dose. A dosing interval of 36 h might be optimal for bactericidal activity and avoid bacterial growth during prolonged periods of extremely low serum gentamicin concentrations; this dosing interval warrants study.

Reevaluation of Gentamicin Dosing in the Neonatal Population

Objective:

To determine whether current recommendations for gentamicin dosing in full-term newborns yield a serum peak concentration of 6–7 μg/mL and a trough concentration less than 2 μg/mL in treating suspected neonatal sepsis.

Design:

Two-year retrospective chart review.

Setting:

Community hospital.

Results:

Sample consisted of 175 newborns with a gestational age ranging from 36 to 43 weeks and 188 sets of concentrations. Pharmacokinetic parameters were calculated using a one-compartment, first-order elimination model and were reported as follows: volume of distribution 0.59 kg/L, elimination rate constant (ke) 0.11 h−1 (half-life [t1/2] 6.8 h) at 36–37 weeks of age, with a significant change (p < 0.05) in rate constant occurring at 38–43 weeks of life, and ke 0.12 h−1 (t1/2 6.0 h) when using a two-tailed, two-sample t-test. Extrapolated mean peak concentrations were 5.8 ± 1.2 μg/mL and trough concentrations were 1.5 ± 0.5 μg/mL. Furthermore, 14% of newborns had an extrapolated trough concentration of 2.0 μg/mL or more.

Conclusions:

The current 2.5-mg/kg dosage is appropriate for the neonatal population studied. However, to decrease the number of potentially toxic trough concentrations, the initial dosing interval should be extended to every 18 hours for full-term neonates (>37 weeks gestation) with normal kidney function and for neonates with a gestational age of 36–37 weeks.