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1.  Urinary tract infection concordance with positive blood and cerebrospinal fluid cultures in the neonatal intensive care unit 
Urinary tract infections (UTI) are common in the neonatal intensive care unit (NICU). Blood, urine, and cerebrospinal fluid (CSF) cultures are frequently obtained to evaluate for infection. We sought to determine the concordance between positive urine cultures and blood or CSF cultures.
Study design
Infants <121 days of age with a UTI admitted to 322 NICUs managed by the Pediatrix Medical Group from 1997–2010 were identified. UTIs were defined by isolation of a single pathogenic organism in a urine sample obtained by catheterization or suprapubic tap. The UTI was concordant if the same organism was identified in the blood or CSF within 3 days of the urine culture.
Of 5681 infants with a urine culture, 984 had 1162 UTIs. Nine hundred seventy-six UTIs (84%) had a blood culture collected within 3 days, and 127 (13%) were concordant. Of the 1162 UTIs, 77 (7%) had a CSF culture collected within 3 days, and 2 (3%) were concordant.
Collection of a urine culture in infants evaluated for late-onset sepsis is important. Concordance was observed in 13% of blood cultures and 3% of CSF cultures. These findings may be related to the initiation of empirical antimicrobial therapy before evaluation for disseminated infection or poor blood culture sensitivity.
PMCID: PMC3549035  PMID: 22935772
infant; sepsis
2.  Group B Streptococcus and Escherichia coli Infections in the Intensive Care Nursery in the Era of Intrapartum Antibiotic Prophylaxis 
Group B Streptococcus (GBS) and Escherichia coli (E. coli) cause serious bacterial infections (SBIs) and are associated with morbidity and mortality in newborn infants. Intrapartum antibiotic prophylaxis (IAP) reduces early-onset SBIs caused by GBS. The effect of IAP on late-onset SBIs caused by these organisms is unknown.
We examined all blood, urine, and cerebrospinal fluid culture results from infants admitted from 1997–2010 to 322 neonatal intensive care units managed by the Pediatrix Medical Group. We identified infants with positive cultures for GBS or E. coli and compared the incidence of early- and late-onset SBI for each organism in the time period before (1997–2001) and after (2002–2010) universal IAP recommendations.
We identified 716,407 infants with cultures, 2520 (0.4%) with cultures positive for GBS and 2476 (0.3%) with cultures positive for E. coli. The incidence of GBS early-onset SBI decreased between 1997–2001 and 2002–2010 from 3.5 to 2.6 per 1000 admissions, and the incidence for E. coli early-onset SBI remained stable (1.4 per 1000 admissions in both time periods). Over the same time period, the incidence of GBS late-onset SBI increased from 0.8 to 1.1 per 1000 admissions, and incidence of E. coli late-onset SBI increased from 2.2 to 2.5 per 1000 admissions.
In our cohort, the incidence of early-onset GBS SBI decreased, while the incidence of late-onset SBI for E. coli and GBS increased.
PMCID: PMC3572304  PMID: 23011013
infection; infant; sepsis; group B Streptococcus; Escherichia coli
3.  Risk Factors for Invasive Candidiasis in Infants >1500 g Birth Weight 
We describe the incidence, risk factors, and outcomes of invasive candidiasis in infants >1500 g birth weight.
We conducted a retrospective cohort study of infants >1500 g birth weight discharged from 305 NICUs in the Pediatrix Medical Group from 2001–2010. Using multivariable logistic regression, we identified risk factors for invasive candidiasis.
Invasive candidiasis occurred in 330/530,162 (0.06%) infants. These were documented from positive cultures from ≥1 of these sources: blood (n=323), cerebrospinal fluid (n=6), or urine from catheterization (n=19). Risk factors included day of life >7 (OR 25.2; 95% CI 14.6–43.3), vaginal birth (OR 1.6 [1.2–2.3]), exposure to broad-spectrum antibiotics (OR 1.6 [1.1–2.4]), central venous line (OR 1.8 [1.3–2.6]), and platelet count <50,000/mm3 (OR 3.7 [2.1–6.7]). All risk factors had poor sensitivities, low positive likelihood ratios, and low positive predictive values. The combination of broad-spectrum antibiotics and low platelet count had the highest positive likelihood ratio (46.2), but the sensitivity of this combination was only 4%. Infants with invasive candidiasis had increased mortality (OR 2.2 [1.3–3.6]).
Invasive candidiasis is uncommon in infants >1500 g birth weight. Infants at greatest risk are those exposed to broad-spectrum antibiotics and with platelet counts of <50,000/mm3.
PMCID: PMC3578110  PMID: 23042050
candidiasis; candidemia; neonates; neonatal intensive care unit
4.  Triazole use in the nursery: fluconazole, voriconazole, posaconazole, and ravuconazole 
Current drug metabolism  2013;14(2):193-202.
Invasive fungal infections in infants admitted to the neonatal intensive care unit are common and often fatal. The mainstay of therapy against invasive fungal infections is antifungal agents. Over the last two decades, the development and approval of these drugs evolved tremendously, and the azole class emerged as important agents in the treatment and prevention of invasive fungal infections. Among the azoles, fluconazole has been used extensively due to its favorable pharmacokinetics, excellent activity against Candida spp, and safety profile. This drug has been well studied in children but data for its use in infants are largely limited to Candida prophylaxis studies. Voriconazole, a second generation triazole, has excellent activity against Candida and Aspergillus spp. However, data on its use in neonates are extremely limited. Posaconazole and Ravuconazole are the newest agents of the triazole family. The antimicrobial spectrum of posaconazole is similar to voriconazole, but with additional activity against zygomycetes. Experience with posaconazole in children is very limited, and there are no reports of its use in infants. Ravuconazole is not approved for use by the FDA but studies in animals and humans show that it is often fungicidal and has favorable pharmacokinetics. In conclusion, the management of invasive fungal infections has progressed greatly over the last two decades with the azole antifungals playing a significant role. Related to this class, future research is needed in order to better assess dosing, safety, schedules and areas of use of these agents in infants admitted to the neonatal intensive care unit.
PMCID: PMC3541435  PMID: 22935068
antifungal agents; triazole; prematurity; infection; candida; aspergillosis
5.  Safety and Effectiveness of Meropenem in Infants With Suspected or Complicated Intra-abdominal Infections 
The safety and effectiveness of meropenem in young infants with suspected or confirmed intra-abdominal infections were evaluated. was well tolerated in this cohort of critically-ill infants, and the majority of infants treated with meropenem (84%) met the definition of therapeutic success.
Background. Intra-abdominal infections are common in young infants and lead to significant morbidity and mortality. Meropenem is a broad-spectrum antimicrobial with excellent activity against pathogens associated with intra-abdominal infections. The purpose of this study was to determine the safety and effectiveness of meropenem in young infants with suspected or complicated intra-abdominal infections.
Methods. Preterm and term infants <91 days of age with suspected or confirmed intra-abdominal infections hospitalized in 24 neonatal intensive care units were studied in an open-label, multiple-dose study. Adverse events and serious adverse events were collected through 3 and 30 days following the last meropenem dose, respectively. Effectiveness was assessed by 3 criteria: death, bacterial cultures, and presumptive clinical cure score.
Results. Of 200 subjects enrolled in the study, 99 (50%) experienced an adverse event, and 34 (17%) had serious adverse events; no adverse events were probably or definitely related to meropenem. The most commonly reported adverse events were sepsis (6%), seizures (5%), elevated conjugated bilirubin (5%), and hypokalemia (5%). Only 2 of the serious adverse events were determined to be possibly related to meropenem (isolated ileal perforation and an episode of fungal sepsis). Effectiveness was evaluable in 192 (96%) subjects, and overall treatment success was 84%.
Conclusions. Meropenem was well tolerated in this cohort of critically ill infants, and the majority of infants treated with meropenem met the definition of therapeutic success.
Clinical Trials Registration. NCT00621192.
PMCID: PMC3491861  PMID: 22955430
6.  Pharmacokinetics and Safety of Fluconazole in Young Infants Supported with Extracorporeal Membrane Oxygenation 
Candida infections are a leading cause of infectious disease-related death in infants supported with extracorporeal membrane oxygenation (ECMO). The ECMO circuit can alter drug pharmacokinetics (PK), thus standard fluconazole dosing in children on ECMO may result in suboptimal drug exposure. This study determined the PK of fluconazole in infants on ECMO.
Infants <120 days old received either intravenous fluconazole prophylaxis (25 mg/kg once a week) or treatment (12 mg/kg daily) while on ECMO. Paired plasma samples were collected pre- and post-oxygenator around doses 1 and 2 to calculate PK indices and describe oxygenator extraction. A 1-compartment model was fit to the data using non-linear regression. Surrogate pharmacodynamic targets for efficacy were evaluated.
Ten infants were enrolled. After dose 1 (n=9), the median clearance was 17 mL/kg/h, the median volume of distribution was 1.5 L/kg, and the median exposure in the first 24 hours (AUC0–24) was 322 h*mg/L. After multiple doses (n=7), the median clearance was 22 mL/kg/h, the median volume of distribution was 1.9 L/kg, and the AUC0–24 was 352 h*mg/L. After dose 1, 78% of infants achieved the prophylaxis target, while only 11% achieved the therapeutic target. Oxygenator extraction of fluconazole was minimal (−2.0%, standard deviation 15.0), and extraction was not correlated with age of the ECMO circuit (rho= − 0.05). There were no adverse events related to fluconazole.
Infants on ECMO had higher volume of distribution but similar clearance when compared with historical controls not on ECMO. In infants on ECMO, a fluconazole dose of 25 mg/kg weekly provides adequate exposure for prophylaxis against Candida infections. However, higher doses may be needed for treatment.
PMCID: PMC3444624  PMID: 22627870
fluconazole; Candida; extracorporeal membrane oxygenation; pharmacokinetics; infants
7.  Pharmacokinetics and Tolerability of Single-Dose Daptomycin in Young Infants 
Daptomycin is approved for the treatment of complicated skin and skin structure infections and Staphylococcus aureus bacteremia. We sought to characterize daptomycin single-dose pharmacokinetics and tolerability in young infants.
Subjects <120 days of age with suspected systemic infections were eligible for inclusion. Each subject was given a single 6 mg/kg intravenous dose of daptomycin. An average of 4 post-dose concentrations per infant was obtained.
Data from 20 infants are presented. Median gestational age at birth and postnatal age were 32 weeks (range 23, 40) and 3 days (1, 85), respectively. The median area under the concentration curve at 24 hours, volume of distribution, total body clearance, and half-life of daptomycin were 262.4 mg*h/L (166.7, 340.2), 0.21 L/kg (0.11, 0.34), 0.021 L/hr/kg (0.016, 0.034), and 6.2 hours (3.7, 9.0), respectively. No adverse events related to daptomycin were observed, including changes in creatine phosphokinase concentrations.
Daptomycin clearance in young infants was similar to that in 2–6-year-olds and higher than that observed in adolescents and adults.
PMCID: PMC3421038  PMID: 22627869
daptomycin; complicated skin and skin structure infections; Staphylococcus aureus; pharmacokinetics
9.  Use of the Complete Blood Cell Count in Early-Onset Neonatal Sepsis 
Early-onset sepsis is an important cause of morbidity and mortality in neonates, and its diagnosis remains challenging. The complete blood cell count and differential have been previously evaluated as diagnostic tools for early-onset sepsis in small, single-center reports. We evaluated the diagnostic accuracy of the complete blood count and differential in early-onset sepsis in a large, multicenter population of neonates admitted to the neonatal intensive care unit.
Using a cohort of 166,092 neonates with suspected early-onset sepsis with cultures admitted to 293 neonatal intensive care units, we calculated odds ratios and receiver operating characteristic curves for complete blood cell count indices and prediction of a positive culture. We determined sensitivity, specificity, and likelihood ratios for various commonly used cut-off values from the complete blood cell count.
Low white blood cell counts, low absolute neutrophil counts, and high immature-to-total neutrophil ratios were associated with increasing odds of infection (highest odds ratios: 5.38, 6.84, and 7.97, respectively). Specificity and negative predictive values were high (73.7–99.9% and >99.8%). However, sensitivities were low (0.3–54.5%) for all complete blood cell count indices analyzed.
Low white blood cell count, absolute neutrophil count, and high immature-to-total neutrophil ratio were associated with increasing odds of infection, but no complete blood cell count-derived index possesses the sensitivity to rule out reliably early-onset sepsis in neonates.
PMCID: PMC3399972  PMID: 22531231
neonatal; early-onset sepsis; blood cell count
10.  Use of the Complete Blood Cell Count in Late-Onset Neonatal Sepsis 
Late-onset sepsis is an important cause of morbidity and mortality in infants. Diagnosis of late-onset sepsis can be challenging. The complete blood cell count and differential have been previously evaluated as diagnostic tools for late-onset sepsis in small, single-center reports.
We evaluated the diagnostic accuracy of the complete blood count and differential in late-onset sepsis in a large multicenter population.
Study design
Using a cohort of all infants with cultures and complete blood cell count data from a large administrative database, we calculated odds ratios for infection, as well as sensitivity, specificity, positive and negative predictive values, and likelihood ratios for various commonly used cut-off values.
High and low white blood cell counts, high absolute neutrophil counts, high immature-to-total neutrophil ratios, and low platelet counts were associated with late-onset sepsis. Associations were weaker with increasing postnatal age at the time of the culture. Specificity was highest for white blood cell counts <1000/mm3 and >50,000/mm3 (>99%). Positive likelihood ratios were highest for white blood cell counts <1000/mm3 (4.1) and platelet counts <50,000/mm3 (3.5).
No complete blood count index possessed adequate sensitivity to reliably rule out late-onset sepsis in this population.
PMCID: PMC3399981  PMID: 22531232
neonatal; late-onset sepsis; blood cell count
11.  Evidence-based guidelines for pediatric clinical trials: focus on StaR Child Health 
Clinical trials in children are challenging and filled with important ethical considerations that differ from adults. Given difficulties associated with pediatric clinical trials, off-label prescribing is a common practice in pediatrics, which can lead to adverse safety events and efficacy failures. To overcome these consequences, in the past 15 years, legislation in the USA and Europe has provided incentives to industry and increased government funding to conduct pediatric trials. Pediatric trial networks have also been formed to decrease the knowledge gap. However, challenges to performing pediatric trials and lack of standardization and guidelines regarding studies in children still exist. Standards for Research (StaR) in Child Health, begun in 2009, aims to improve the design, conduct and reporting of pediatric trials. This organization uses a consensus guideline approach involving academic, government and industry stakeholders to identify and disseminate best practices for pediatric trials. Six out of 11 planned standards are currently published.
PMCID: PMC3566240  PMID: 23121275
clinical trials; guidelines; pediatrics
12.  Population Pharmacokinetics of Piperacillin Using Scavenged Samples from Preterm Infants 
Therapeutic Drug Monitoring  2012;34(3):312-319.
Piperacillin is often used in preterm infants for intra-abdominal infections; however, dosing has been derived from small single-center studies excluding extremely preterm infants at highest risk for these infections. We evaluated the population pharmacokinetics (PK) of piperacillin using targeted sparse sampling and scavenged samples obtained from preterm infants ≤32 weeks gestational age at birth and <120 postnatal days.
Materials and Methods
A 5-center study was performed. A population PK model using nonlinear mixed effect modeling was developed. Covariate effects were evaluated based on estimated precision and clinical significance.
Fifty-six preterm infants were evaluated and had a median (range) gestational age at birth of 25 (22–32) weeks, a postnatal age of 17 (1–77) days, a postmenstrual age of 29 (23–40) weeks, and a weight of 867 (400–2580) grams. The final PK data set contained 211 samples; 202/211 (96%) were scavenged from discarded clinical specimens. Piperacillin population PK was best described by a 1-compartment model. The population mean clearance (CL) was derived by the equation CL (liter/h)=0.479 x (weight)0.75 x 0.5/serum creatinine and using a volume of distribution (V) (liter) of 2.91 x (weight). The relative standard errors around parameter estimates ranged from 13.7–32.2%. A trend towards increased CL was observed with increasing gestational age at birth; infants with serum creatinine ≥1.2 mg/dL had a 60% reduction in piperacillin CL. The majority (>70%) of infants did not meet pre-defined pharmacodynamic efficacy targets.
Scavenged PK sampling is a minimal-risk approach that can provide meaningful information related to development of PK models but not dosing recommendations for piperacillin. The utility of scavenged sampling in providing definitive dosing recommendations may be drug-dependent and needs to be further explored.
PMCID: PMC3354042  PMID: 22569355
neonate; drug; pharmacokinetics; piperacillin
14.  Therapeutic Monitoring of Voriconazole in Children Less Than 3 Years of Age: A Case Report and Summary of Voriconazole Concentrations for 10 Children 
Voriconazole is the treatment of choice for invasive aspergillosis and its use is increasing in pediatrics. Minimal pharmacokinetic data exist in young children. We report voriconazole concentrations for 10 children less than <3 years of age and pharmacokinetic parameters for one infant who had therapeutic drug monitoring performed. Trough concentrations were unpredictable based on dose, highlighting the need to follow values during therapy.
PMCID: PMC3356483  PMID: 22301479
invasive aspergillosis; pediatric; voriconazole; pharmacokinetic; therapeutic drug monitoring
15.  Antifungal Therapy and Outcomes in Infants with Invasive Candida Infections 
Invasive candidiasis is a leading cause of mortality and morbidity in neonatal intensive care units. Treatment recommendations are limited by a lack of comparative outcomes data.
We identified all infants ≤120 days of age with positive blood, urine, or cerebrospinal fluid cultures for Candida sp. who received amphotericin B deoxycholate, fluconazole, amphotericin B lipid products, or combination therapy admitted to 1 of 192 neonatal intensive care units in the United States between 1997 and 2003. Primary outcome measures included overall mortality and therapeutic failure (combined outcome of duration of infection >7 days, need for additional antifungal therapy, or death prior to discharge). We compared outcomes by antifungal therapy using logistic regression, controlling for gestational age, day of life at start of antifungal therapy, delay in therapy, and site of infection.
Overall, 138/730 (19%) infants died. On multivariable logistic regression, we observed higher overall mortality for infants receiving amphotericin B lipid products compared with infants receiving amphotericin B deoxycholate (OR 1.96 [95% CI: 1.16, 3.33]; p=0.01) or fluconazole (OR 2.39 [1.18, 4.83]; p=0.02).
Infants treated with amphotericin B lipid products had higher mortality than infants treated with either amphotericin B deoxycholate or fluconazole. This finding may be related to inadequate penetration of amphotericin B lipid products into the kidneys, inappropriate dosing in premature infants, or unknown differences in acuity of illness in infants treated with amphotericin B lipid products.
PMCID: PMC3329577  PMID: 22189522
invasive candidiasis; infants; amphotericin B deoxycholate; fluconazole; amphotericin B lipid products
16.  Early and Late Onset Sepsis in Very-Low-Birth-Weight Infants from a Large Group of Neonatal Intensive Care Units 
Early human development  2012;88(Suppl 2):S69-S74.
Very-low-birth-weight (VLBW, <1500 g birth weight) infants are at high risk for both early- and late-onset sepsis. Prior studies have observed a predominance of gram-negative organisms as a cause of early-onset sepsis and gram-positive organisms as a cause of late-onset sepsis. These reports are limited to large, academic neonatal intensive care units (NICUs) and may not reflect findings in other units. The purpose of this study was to determine the risk factors for sepsis, the causative organisms, and mortality following infection in a large and diverse sample of NICUs.
We analyzed the results of all cultures obtained from VLBW infants admitted to 313 NICUs from 1997 to 2010.
Over 108,000 VLBW infants were admitted during the study period. Early-onset sepsis occurred in 1032 infants, and late-onset sepsis occurred in 12,204 infants. Gram-negative organisms were the most commonly isolated pathogens in early-onset sepsis, and gram-positive organisms were most commonly isolated in late-onset sepsis. Early- and late-onset sepsis were associated with increased risk of death controlling for other confounders (odds ratio 1.45 [95% confidence interval 1.21, 1.73], and OR 1.30 [95% CI 1.21, 1.40], respectively).
This is the largest report of sepsis in VLBW infants to date. Incidence for early-onset sepsis and late-onset sepsis has changed little over this 14-year period, and overall mortality in VLBW infants with early- and late-onset sepsis is higher than in infants with negative cultures.
PMCID: PMC3513766  PMID: 22633519
early-onset sepsis; late-onset sepsis; very-low-birth-weight infants
17.  Sepsis in Young Infants with Congenital Heart Disease 
Early human development  2012;88(Suppl 2):S92-S97.
We sought to describe the incidence, pathogen distribution, and mortality associated with blood culture-proven sepsis in young infants with congenital heart disease (CHD) admitted to a neonatal intensive care unit (NICU).
Cohort study of all blood cultures obtained from infants with CHD between 4 and 120 days of age cared for in250 NICUs managed by the Pediatrix Medical Group in the United States between 1996 and 2007.
Of 11,638 infants with CHD, 656 (6%) had 821 episodes of sepsis: a cumulative incidence of 71/1000 admissions. Gram-positive organisms were the most common cause (64%), and coagulase-negative Staphylococcus and Staphylococcus aureus were the most frequently isolated species. On multivariable regression, infants with sepsis were more likely to die compared to infants with sterile blood cultures (odds ratio [OR] = 1.53 [95% confidence interval: 1.09, 2.13]). Infants with gram-negative bacteremia and candidemia were more likely to die than infants with sterile blood cultures (OR = 2.01 [1.20, 3.37], and OR = 3.18 [1.60, 6.34], respectively).
Infants with CHD have a high incidence of culture-proven sepsis, especially with staphylococcal organisms. Gram-negative bacteremia and candidemia are strongly associated with increased mortality in this group of young infants.
PMCID: PMC3513769  PMID: 22633525
infant; sepsis; infection; congenital heart disease; epidemiology; outcomes
18.  Very Late Onset Infections in the Neonatal Intensive Care Unit 
Early Human Development  2011;88(4):217-225.
We sought to determine the risk factors, incidence, and mortality of very late onset bacterial infection (blood, urine, or cerebrospinal fluid culture positive occurring after day of life 120) in preterm infants.
A retrospective observational cohort study of all very low birth weight infants cared for between day of life 120 and 365 in 292 neonatal intensive care units in the United States from 1997 to 2008.
We identified 3918 infants who were hospitalized beyond 120 days of life. Of these, 1027 (26%) were evaluated with at least 1 culture (blood, urine, or cerebrospinal fluid), and 276 (27%) of the evaluated infants had 414 episodes of culture-positive infection. Gram-positive organisms caused most of the infections (48%). The risk of death was higher in infants with positive cultures (odds ratio; 10.5, 95% confidence interval [7.2–15.5]) or negative cultures (4.8, [3.5–6.7]) compared to infants that were never evaluated with a culture (p<0.001). Mortality was highest with fungal infections (8/24, 33%) followed by Gram-positive cocci (40/142, 28%).
Important predictive risk factors for early and late onset sepsis (birth weight and gestational age) did not contribute to risk of developing very late onset infection. Evaluation for infection (whether positive or negative) was a significant risk factor for death. GPC and fungal infections were associated with high mortality.
PMCID: PMC3248995  PMID: 21924568
Neonate; VLBW; sepsis; late onset
19.  Pharmacokinetics of Moxifloxacin in an Infant with Mycoplasma hominis Meningitis 
Treatment of Mycoplasma hominis meningitis in infants is limited by a lack of consensus regarding therapy and limited pharmacokinetic data for agents to which M. hominis is susceptible. We report the successful treatment of a premature infant with M. hominis meningitis with doxycycline and moxifloxacin and provide a pharmacokinetic profile of moxifloxacin.
PMCID: PMC3358780  PMID: 22016080
meningitis; moxifloxacin; Mycoplasma hominis; infant; pharmacokinetic
20.  Development of a Liquid Chromatography-Tandem Mass Spectrometry Assay of Six Antimicrobials in Plasma for Pharmacokinetic Studies in Premature Infants 
This method provides a simple extraction procedure, as well as a validated, sensitive, and specific liquid chromatography-tandem mass spectrometry assay for the simultaneous quantification of ampicillin, piperacillin, tazobactam, meropenem, acyclovir, and metronidazole in human plasma. The method was validated over concentration ranges specific for each compound, with a lower limit of quantification of 50–300 ng/mL and a sample volume of 50 μL. The method is accurate and precise, with within- and between-day accuracy ranging from 85–110% and 92–110%, respectively, and within- and between-day precision of 89–111% and 91–109%, respectively. Simplicity, low plasma volume, and high throughput make this method suitable for clinical pharmacokinetic studies in premature infants.
PMCID: PMC3210405  PMID: 21983195
prematurity; neonates; antibiotics; antivirals; HPLC; mass spectrometry
21.  Population Pharmacokinetics of Meropenem in Plasma and Cerebrospinal Fluid of Infants with Suspected or Complicated Intra-Abdominal Infections 
Suspected or complicated intra-abdominal infections are common in young infants and lead to significant morbidity and mortality. Meropenem is a broad-spectrum antimicrobial agent with excellent activity against pathogens associated with intra-abdominal infections in this population. The purpose of this study was to determine the pharmacokinetics (PK) of meropenem in young infants as a basis for optimizing dosing and minimizing adverse events.
Premature and term infants <91 days of age hospitalized in 24 neonatal intensive care units were studied. Limited PK sampling was performed following single and multiple doses of meropenem 20–30 mg/kg of body weight every 8–12 hours based on postnatal and gestational age at birth. Population and individual patient (Bayesian) PK parameters were estimated using NONMEM®.
Two hundred infants were enrolled and received study drug. One hundred eighty-eight infants with 780 plasma meropenem concentrations were analyzed. Their median (range) gestational age at birth and postnatal age at PK evaluation were 28 (23–40) weeks and 21 (1–92) days, respectively. In the final PK model, meropenem clearance (CL) was strongly associated with serum creatinine (SCR) and postmenstrual age (PMA) (CL [L/h/kg] = 0.12*[(0.5/SCR)**0.27]*[(PMA/32.7)**1.46]). Meropenem concentrations remained >4 μg/mL for 50% of the dose interval and >2 μg/mL for 75% of the dose interval in 96% and 92% of patients, respectively. The estimated penetration of meropenem into the cerebrospinal fluid was 70% (5–148).
Meropenem dosing strategies based on postnatal and gestational age achieved therapeutic drug exposure in almost all infants.
PMCID: PMC3173561  PMID: 21829139
enterocolitis; necrotizing; infant; premature; cerebrospinal fluid
22.  Population Pharmacokinetics of Metronidazole Evaluated Using Scavenged Samples from Preterm Infants 
Pharmacokinetic (PK) studies in preterm infants are rarely conducted due to the research challenges posed by this population. To overcome these challenges, minimal-risk methods such as scavenged sampling can be used to evaluate the PK of commonly used drugs in this population. We evaluated the population PK of metronidazole using targeted sparse sampling and scavenged samples from infants that were ≤32 weeks of gestational age at birth and <120 postnatal days. A 5-center study was performed. A population PK model using nonlinear mixed-effect modeling (NONMEM) was developed. Covariate effects were evaluated based on estimated precision and clinical significance. Using the individual Bayesian PK estimates from the final population PK model and the dosing regimen used for each subject, the proportion of subjects achieving the therapeutic target of trough concentrations >8 mg/liter was calculated. Monte Carlo simulations were performed to evaluate the adequacy of different dosing recommendations per gestational age group. Thirty-two preterm infants were enrolled: the median (range) gestational age at birth was 27 (22 to 32) weeks, postnatal age was 41 (0 to 97) days, postmenstrual age (PMA) was 32 (24 to 43) weeks, and weight was 1,495 (678 to 3,850) g. The final PK data set contained 116 samples; 104/116 (90%) were scavenged from discarded clinical specimens. Metronidazole population PK was best described by a 1-compartment model. The population mean clearance (CL; liter/h) was determined as 0.0397 × (weight/1.5) × (PMA/32)2.49 using a volume of distribution (V) (liter) of 1.07 × (weight/1.5). The relative standard errors around parameter estimates ranged between 11% and 30%. On average, metronidazole concentrations in scavenged samples were 30% lower than those measured in scheduled blood draws. The majority of infants (>70%) met predefined pharmacodynamic efficacy targets. A new, simplified, postmenstrual-age-based dosing regimen is recommended for this population. Minimal-risk methods such as scavenged PK sampling provided meaningful information related to development of metronidazole PK models and dosing recommendations.
PMCID: PMC3318328  PMID: 22252819
23.  Pharmacokinetics of Antifungal Agents in Children 
Early human development  2011;87(Suppl 1):S61-S65.
Invasive fungal infections in immunocompromised children are common and often fatal. The first antifungal agents such as amphotericin B and fluconazole offered effective treatment, but their use was often limited by toxicity and resistance. Numerous new antifungal agents have since been developed and appear to be as effective. Most dosing and safety trials have been done in adults, and extrapolation of this data to children has proven inadequate. We reviewed the literature regarding the pharmacokinetics/pharmacodynamics (PK/PD) and safety of antifungal agents with an emphasis on the newer azoles and echinocandins. From a small but growing number of PK/PD trials, better dosing guidelines have been developed.
PMCID: PMC3418808  PMID: 21277714
antifungal agents; pharmacology; pharmacokinetics; neonates; infants; children
24.  Pediatric Cardiovascular Drug Dosing in Critically Ill Children and Extracorporeal Membrane Oxygenation 
Cardiovascular disease in children is common and results in significant morbidity and mortality. The sickest children with cardiovascular disease may require support with extracorporeal membrane oxygenation (ECMO) which provides life-saving assistance for children with refractory cardiorespiratory failure. Many classes of cardiovascular drugs are used in children, but very few of these agents have been well studied in children. The knowledge gap is even more pronounced in children supported with ECMO. Pharmacokinetic (PK) data collected to date (primarily from antibiotics and sedatives) suggest that the ECMO circuit has the potential to significantly alter the pharmacokinetics of drugs including changes in clearance and volume of distribution. Of all cardiovascular drugs administered to children supported by ECMO, only 11 have been partially studied and reported in the medical literature. Esmolol, amiodarone, nesiritide, bumetanide, sildenafil, and prostaglandin E1 appear to require dosing modifications in children supported by ECMO, while it appears that hydralazine, nicardipine, furosemide, epinephrine, and dopamine can be dosed similarly to children not supported by ECMO. However, trials evaluating the PK of these drugs in patients supported by ECMO are extremely limited (i.e. case reports) and therefore definitive dosing recommendations are not plausible. Research efforts should focus on evaluating the PK of drugs in patients on ECMO in order to avoid therapeutic failures or unnecessary toxicities.
PMCID: PMC3155009  PMID: 21346597
cardiovascular agents; extracorporeal membrane oxygenation; pharmacology; pharmacokinetics
25.  Anidulafungin for Neonatal Hematogenous Candida Meningoencephalitis: Identification of Candidate Regimens for Humans Using a Translational Pharmacological Approach 
Hematogenous Candida meningoencephalitis (HCME) is a serious infection in premature neonates. Anidulafungin is an echinocandin antifungal agent with potent activity against Candida spp., but its efficacy and optimal regimens for human neonates with HCME are not known. A well-validated rabbit model of HCME was used to define pharmacokinetic-pharmacodynamic (PK-PD) relationships of anidulafungin. A mathematical model was fitted to the entire data set. The experimental data were bridged to humans. A population PK model was fitted to the data from human neonates receiving anidulafungin receiving a loading dose of 3 mg/kg, followed by 1.5 mg/kg/day. Monte Carlo simulations were performed to identify candidate anidulafungin regimens for humans. All untreated rabbits succumbed by ≤96 h postinoculation. The PK of anidulafungin was linear with dose-dependent penetration into the cerebrum. Anidulafungin exerted a rapid antifungal effect that was apparent in the first dosing interval. Near-maximal antifungal activity was observed with dosages of 10 to 20 mg/kg/day. The bridging studies suggested that the current regimen of first 3 mg/kg, followed by 1.5 mg/kg/day, is suboptimal. Higher dosages were associated with progressively greater antifungal effect. Anidulafungin is effective for the treatment of experimental HCME. Higher dosages than those currently used for clinical care are required for maximal antifungal effect.
PMCID: PMC3264209  PMID: 22123680

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