Background

High doses of ampicillin are often used to achieve therapeutic drug concentrations in infants. A paradoxical antibiotic effect, often called the Eagle effect, occurs when increasing concentrations of antibiotic above a threshold results in decreased efficacy. It is unknown if infants treated with ampicillin are at risk for this paradoxical effect.

Methods

We identified infants <28 days of age with Escherichia coli, Enterococcus or Streptococcus agalactiae (group B streptococcus) bloodstream infections from 1997 to 2012 and previously included in an ampicillin pharmacokinetic (PK) modeling study. We compared the odds of death for ampicillin dose, estimated time above the minimum inhibitory concentration (T > MIC) and PK parameters using separate logistic regression models. Adjusted logistic regression and Poisson models were used to calculate the odds of prolonged bacteremia ≥3 days and the duration of bacteremia, respectively, for dose, T > MIC and multiple PK parameters.

Results

Among 1272 infants meeting inclusion criteria, odds of death 7 or 30 days after the positive blood culture were not consistent with a paradoxical effect across any of the dosing regimens or PK parameters evaluated. The odds of prolonged bacteremia was lowest at the lowest dose category and the lowest daily dose category but not associated with the area-under-the-concentration time curve from 0 to 24 hours, or the maximum or minimum concentrations at steady state. T > MIC of ≥50% of the dosing interval was associated with decreased duration of bacteremia and odds of prolonged bacteremia.

Conclusions

It is unlikely that a paradoxical antibiotic effect will have a clinical correlate when ampicillin is used for neonatal bacteremia. A T > MIC ≥50% decreased both duration of bacteremia and odds of prolonged bacteremia.

Metoclopramide is commonly used for gastroesophageal reflux. The aims of the present study were to develop a pediatric population pharmacokinetic (PopPK) model, which was applied to simulate the metoclopramide exposure following dosing used in clinical practice. Opportunistic pharmacokinetic data were collected from pediatric patients receiving enteral or parenteral metoclopramide per standard of care and these data were simultaneously fitted using NONMEM. Allometric scaling with body weight was included a priori in the model. Using the final model, the steady-state maximum concentrations (C_ss,max ) and the area under the metoclopramide plasma concentration-time curve at steady state from 0 to 6 hours (AUC_ss,0-6h ) were simulated following 0.1 or 0.15 mg/kg orally every 6 hours in virtual patients, and compared with previously reported ranges associated with toxicity or the efficacy for gastroesophageal reflux in infants. A two-compartment model with first-order absorption best characterized 87 concentration measurements from 50 patients (median [range] postnatal age of 8.89 years [0.01-19.13]). There were 20 infants (≤ 2 years), 9 children (2 years to age ≤ 12 years), and 21 adolescents (> 12 years). Body weight was the only covariate included in the final model. For > 75% of virtual patients, simulated C_ss,max and AUC_ss,0-6h estimates were within the range associated with efficacy for gastroesophageal reflux in infants; however, slightly lower exposures were predicted in virtual patients < 2 years. Our study suggests that a metoclopramide enteral dose of 0.1 mg/kg every 6 hours, which was previously recommended for pediatric patients, results in simulated exposure generally within suggested ranges for the treatment of gastroesophageal reflux.