Kevin M. Watt

Early and late onset sepsis in very-low-birth-weight infants from a large group of neonatal intensive care units.

BACKGROUND 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. METHODS We analysed the results of all cultures obtained from VLBW infants admitted to 313 NICUs from 1997 to 2010. RESULTS 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 [CI] 1.21,1.73], and OR 1.30 [95%CI 1.21, 1.40], respectively). CONCLUSIONS 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.

Changing Epidemiology of Serious Bacterial Infections in Febrile Infants without Localizing Signs

Objective Historically, management of infants with fever without localizing signs (FWLS) has generated much controversy, with attempts to risk stratify based on several criteria. Advances in medical practice may have altered the epidemiology of serious bacterial infections (SBIs) in this population. We conducted this study to test the hypothesis that the rate of SBIs in this patient population has changed over time. Patients and Methods We performed a retrospective review of all infants meeting FWLS criteria at our institution from 1997–2006. We examined all clinical and outcome data and performed statistical analysis of SBI rates and ampicillin resistance rates. Results 668 infants met criteria for FWLS. The overall rate of SBIs was 10.8%, with a significant increase from 2002–2006 (52/361, 14.4%) compared to 1997–2001 (20/307, 6.5%) (p = 0.001). This increase was driven by an increase in E. coli urinary tract infections (UTI), particularly in older infants (31–90 days). Conclusions We observed a significant increase in E. coli UTI among FWLS infants with high rates of ampicillin resistance. The reasons are likely to be multifactorial, but the results themselves emphasize the need to examine urine in all febrile infants <90days and consider local resistance patterns when choosing empiric antibiotics.

Antifungal Therapy and Outcomes in Infants with Invasive Candida Infections

Background: 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. Methods: We identified all infants ⩽120 days of age with positive blood, urine, or cerebrospinal fluid cultures for Candida species who received amphotericin B deoxycholate, fluconazole, amphotericin B lipid products, or combination therapy admitted to one 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 before 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. Results: Overall, 138 of 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 (odds ratio 1.96 [95% confidence intervals: 1.16, 3.33]; P = 0.01) or fluconazole (odds ratio 2.39 [1.18, 4.83]; P = 0.02). Conclusions: 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.

Developmental Pharmacokinetics of Piperacillin and Tazobactam Using Plasma and Dried Blood Spots from Infants

ABSTRACT Piperacillin-tazobactam is often given to infants with severe infection in spite of limited pharmacokinetics (PK) data. We evaluated piperacillin-tazobactam PK in premature and term infants of ages <61 days with suspected systemic infection. Infants received intravenous piperacillin-tazobactam (80 to 100 mg/kg of body weight every 8 h [q 8 h]) based on gestational and postnatal age. Sparse plasma samples were obtained after first and multiple doses. Drug concentrations were measured by tandem mass spectrometry. PK data were analyzed using population nonlinear mixed-effect modeling. Target attainment rates for the time unbound piperacillin concentrations remained above the MIC for 50% and 75% of the dosing interval at steady state were evaluated. Bias in population PK parameter estimates was assessed for dried blood spot (DBS) samples, and a comparability analysis was performed for DBS and plasma drug concentrations using linear regression. We obtained 128 plasma samples from 32 infants, median gestational age of 30 weeks (range, 23 to 40 weeks) and postnatal age of 8 days (range, 1 to 60). Piperacillin and tazobactam PK models included body weight (WT) and postmenstrual age (PMA) as covariates for clearance and WT for volume of distribution and were used to optimize dosing in infants. DBS drug concentrations were 50 to 60% lower than those in plasma, but when combined with plasma concentrations and a matrix effect, the data generated PK model parameters similar to those for plasma alone. With PMA-based dosing (100 mg/kg q 8 h, 80 mg/kg q 6 h, and 80 mg/kg q 4 h for PMA of ≤30, 30 to 35, and 35 to 49 weeks, respectively), 90% of simulated infants achieved the surrogate therapeutic target of time above the MIC (≤32 mg/liter) for 75% of the dosing interval.

Use of opportunistic clinical data and a population pharmacokinetic model to support dosing of clindamycin for premature infants to adolescents.

Clindamycin is commonly prescribed to treat children with skin and skin‐structure infections (including those caused by community‐acquired methicillin‐resistant Staphylococcus aureus (CA‐MRSA)), yet little is known about its pharmacokinetics (PK) across pediatric age groups. A population PK analysis was performed in NONMEM using samples collected in an opportunistic study from children receiving i.v. clindamycin per standard of care. The final model was used to optimize pediatric dosing to match adult exposure proven effective against CA‐MRSA. A total of 194 plasma PK samples collected from 125 children were included in the analysis. A one‐compartment model described the data well. The final model included body weight and a sigmoidal maturation relationship between postmenstrual age (PMA) and clearance (CL): CL (l/h) = 13.7 × (weight/70)0.75 × (PMA3.1/(43.63.1 + PMA3.1)); V (l) = 61.8 × (weight/70). Maturation reached 50% of adult CL values at ~44 weeks PMA. Our findings support age‐based dosing.

Safety and effectiveness of meropenem in infants with suspected or complicated intra-abdominal infections.

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.

Pharmacokinetics and tolerability of single-dose daptomycin in young infants.

Background: 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. Methods: 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 postdose concentrations per infant was obtained. Results: 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/h/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. Conclusions: Daptomycin clearance in young infants was similar to that in children 2–6 years of age and higher than that observed in adolescents and adults.

Drug Dosing and Pharmacokinetics in Children With Obesity: A Systematic Review

IMPORTANCE Obesity affects nearly one-sixth of US children and results in alterations to body composition and physiology that can affect drug disposition, possibly leading to therapeutic failure or toxic side effects. The depth of available literature regarding obesitys effect on drug safety, pharmacokinetics, and dosing in obese children is unknown. OBJECTIVE To perform a systematic literature review describing the current evidence of the effect of obesity on drug disposition in children. EVIDENCE REVIEW We searched the MEDLINE, Cochrane, and EMBASE databases (January 1, 1970-December 31, 2012) and included studies if they contained data on drug clearance, volume of distribution, or drug concentration in obese children (aged ≤18 years). We compared exposure and weight-normalized volume of distribution and clearance between obese and nonobese children. We explored the association between drug physicochemical properties and clearance and volume of distribution. FINDINGS Twenty studies met the inclusion criteria and contained pharmacokinetic data for 21 drugs. The median number of obese children studied per drug was 10 (range, 1-112) and ages ranged from newborn to 29 years (1 study described pharmacokinetics in children and adults together). Dosing schema varied and were either a fixed dose (6 [29%]) or based on body weight (10 [48%]) and body surface area (4 [19%]). Clinically significant pharmacokinetic alterations were observed in obese children for 65% (11 of 17) of the studied drugs. Pharmacokinetic alterations resulted in substantial differences in exposure between obese and nonobese children for 38% (5 of 13) of the drugs. We found no association between drug lipophilicity or Biopharmaceutical Drug Disposition Classification System class and changes in volume of distribution or clearance due to obesity. CONCLUSIONS AND RELEVANCE Consensus is lacking on the most appropriate weight-based dosing strategy for obese children. Prospective pharmacokinetic trials in obese children are needed to ensure therapeutic efficacy and enhance drug safety.

Pharmacokinetics and safety of fluconazole in young infants supported with extracorporeal membrane oxygenation.

Background: 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; thus, standard fluconazole dosing in children on ECMO may result in suboptimal drug exposure. This study determined the pharmacokinetics of fluconazole in infants on ECMO. Methods: Infants <120 days of age 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 preoxygenator and postoxygenator around doses 1 and 2 to calculate pharmacokinetic indices and describe oxygenator extraction. A 1-compartment model was fit to the data using nonlinear regression. Surrogate pharmacodynamic targets for efficacy were evaluated. Results: 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 (area under the curve from 0 to 24 hours) 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 area under the curve from 0 to 24 hours was 352 h × mg/L. After dose 1, 78% of infants achieved the prophylaxis target, whereas 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 (&rgr;= –0.05). There were no adverse events related to fluconazole. Conclusions: 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.

Treatment and Prophylaxis of Invasive Candidiasis

Invasive candidiasis (IC) is a leading cause of morbidity and mortality in preterm infants. Even if successfully treated, IC can cause significant neurodevelopmental impairment. Preterm infants are at increased risk for hematogenous Candida meningoencephalitis owing to increased permeability of the blood-brain barrier, so antifungal treatment should have adequate central nervous system penetration. Amphotericin B deoxycholate, lipid preparations of amphotericin B, fluconazole, and micafungin are first-line treatments of IC. Fluconazole prophylaxis reduces the incidence of IC in extremely premature infants, but its safety has not been established for this indication, and as yet, the product has not been shown to reduce mortality in neonates. Targeted prophylaxis may have a role in reducing the burden of disease in this vulnerable population.