Cost-effectiveness analysis of heart rate characteristics monitoring to improve survival for very low birth weight infants.

Introduction: Over 50,000 very low birth weight (VLBW) infants are born each year in the United States. Despite advances in care, these premature babies are subjected to long stays in a neonatal intensive care unit (NICU), and experience high rates of morbidity and mortality. In a large randomized controlled trial (RCT), heart rate characteristics (HRC) monitoring in addition to standard monitoring decreased all-cause mortality among VLBW infants by 22%. We sought to understand the cost-effectiveness of HRC monitoring to improve survival among VLBW infants. Methods: We performed a secondary analysis of cost-effectiveness of heart rate characteristics (HRC) monitoring to improve survival from birth to NICU discharge, up to 120 days using data and outcomes from an RCT of 3,003 VLBW patients. We estimated each patient's cost from a third-party perspective in 2021 USD using the resource utilization data gathered during the RCT (NCT00307333) during their initial stay in the NICU and applied to specific per diem rates. We computed the incremental cost-effectiveness ratio and used non-parametric boot-strapping to evaluate uncertainty. Results: The incremental cost-effectiveness ratio of HRC-monitoring was $34,720 per life saved. The 95th percentile of cost to save one additional life through HRC-monitoring was $449,291. Conclusion: HRC-monitoring appears cost-effective for increasing survival among VLBW infants.

Multivariable Predictive Models of Death or Neurodevelopmental Impairment Among Extremely Low Birth Weight Infants Using Heart Rate Characteristics.

OBJECTIVE: We hypothesized that a cumulative heart rate characteristics (HRC) index in real-time throughout the neonatal intensive care unit (NICU) hospitalization, alone or combined with birth demographics and clinical characteristics, can predict a composite outcome of death or neurodevelopmental impairment (NDI). STUDY DESIGN: We performed a retrospective analysis using data from extremely low birth weight infants who were monitored for HRC during neonatal intensive care. Surviving infants were assessed for NDI at 18-22 months of age. Multivariable predictive modeling of subsequent death or NDI using logistic regression, cross-validation with repeats, and step-wise feature elimination was performed each postnatal day through day 60. RESULTS: Among the 598 study participants, infants with the composite outcome of death or moderate-to-severe NDI had higher mean HRC scores during their stay in the NICU (3.1 ± 1.8 vs 1.3 ± 0.8; P < .001). Predictive models for subsequent death or NDI were consistently higher when the cumulative mean HRC score was included as a predictor variable. A parsimonious model including birth weight, sex, ventilatory status, and cumulative mean HRC score had a cross-validated receiver-operator characteristic curve as high as 0.84 on days 4, 5, 6, and 8 and as low as 0.78 on days 50-52 and 56-58 to predict subsequent death or NDI. CONCLUSIONS: In extremely low birth weight infants, higher mean HRC scores throughout their stay in the NICU were associated with a higher risk of the composite outcome of death or NDI. TRIAL REGISTRATION: ClinicalTrials.gov: NCT00307333.

Single-Examination Risk Prediction of Severe Retinopathy of Prematurity.

BACKGROUND AND OBJECTIVES: Retinopathy of prematurity (ROP) is a leading cause of childhood blindness. Screening and treatment reduces this risk, but requires multiple examinations of infants, most of whom will not develop severe disease. Previous work has suggested that artificial intelligence may be able to detect incident severe disease (treatment-requiring retinopathy of prematurity [TR-ROP]) before clinical diagnosis. We aimed to build a risk model that combined artificial intelligence with clinical demographics to reduce the number of examinations without missing cases of TR-ROP. METHODS: Infants undergoing routine ROP screening examinations (1579 total eyes, 190 with TR-ROP) were recruited from 8 North American study centers. A vascular severity score (VSS) was derived from retinal fundus images obtained at 32 to 33 weeks' postmenstrual age. Seven ElasticNet logistic regression models were trained on all combinations of birth weight, gestational age, and VSS. The area under the precision-recall curve was used to identify the highest-performing model. RESULTS: The gestational age + VSS model had the highest performance (mean ± SD area under the precision-recall curve: 0.35 ± 0.11). On 2 different test data sets (n = 444 and n = 132), sensitivity was 100% (positive predictive value: 28.1% and 22.6%) and specificity was 48.9% and 80.8% (negative predictive value: 100.0%). CONCLUSIONS: Using a single examination, this model identified all infants who developed TR-ROP, on average, >1 month before diagnosis with moderate to high specificity. This approach could lead to earlier identification of incident severe ROP, reducing late diagnosis and treatment while simultaneously reducing the number of ROP examinations and unnecessary physiologic stress for low-risk infants.

Heart rate characteristics monitoring and reduction in mortality or neurodevelopmental impairment in extremely low birthweight infants with sepsis.

We questioned whether a heart rate characteristics (HRC) sepsis risk score displayed to clinicians would modify 18-22 month neurodevelopmental outcomes for extremely low birthweight infants who develop sepsis. Infants allocated to HRC display with sepsis had a 12% absolute reduction in the composite outcome of death or neurodevelopmental impairment. TRIAL REGISTRATION: NCT00307333.

Quantification of Early Neonatal Oxygen Exposure as a Risk Factor for Retinopathy of Prematurity Requiring Treatment.

Purpose: Retinopathy of prematurity (ROP) is a leading cause of childhood blindness related to oxygen exposure in premature infants. Since oxygen monitoring protocols have reduced the incidence of treatment-requiring ROP (TR-ROP), it remains unclear whether oxygen exposure remains a relevant risk factor for incident TR-ROP and aggressive ROP (A-ROP), a severe, rapidly progressing form of ROP. The purpose of this proof-of-concept study was to use electronic health record (EHR) data to evaluate early oxygen exposure as a predictive variable for developing TR-ROP and A-ROP. Design: Retrospective cohort study. Participants: Two hundred forty-four infants screened for ROP at a single academic center. Methods: For each infant, oxygen saturations and fraction of inspired oxygen (FiO2) were extracted manually from the EHR until 31 weeks postmenstrual age (PMA). Cumulative minimum, maximum, and mean oxygen saturation and FiO2 were calculated on a weekly basis. Random forest models were trained with 5-fold cross-validation using gestational age (GA) and cumulative minimum FiO2 at 30 weeks PMA to identify infants who developed TR-ROP. Secondary receiver operating characteristic (ROC) curve analysis of infants with or without A-ROP was performed without cross-validation because of small numbers. Main Outcome Measures: For each model, cross-validation performance for incident TR-ROP was assessed using area under the ROC curve (AUC) and area under the precision-recall curve (AUPRC) scores. For A-ROP, we calculated AUC and evaluated sensitivity and specificity at a high-sensitivity operating point. Results: Of the 244 infants included, 33 developed TR-ROP, of which 5 developed A-ROP. For incident TR-ROP, random forest models trained on GA plus cumulative minimum FiO2 (AUC = 0.93 ± 0.06; AUPRC = 0.76 ± 0.08) were not significantly better than models trained on GA alone (AUC = 0.92 ± 0.06 [P = 0.59]; AUPRC = 0.74 ± 0.12 [P = 0.32]). Models using oxygen alone showed an AUC of 0.80 ± 0.09. ROC analysis for A-ROP found an AUC of 0.92 (95% confidence interval, 0.87-0.96). Conclusions: Oxygen exposure can be extracted from the EHR and quantified as a risk factor for incident TR-ROP and A-ROP. Extracting quantifiable clinical features from the EHR may be useful for building risk models for multiple diseases and evaluating the complex relationships among oxygen exposure, ROP, and other sequelae of prematurity.

Preimmune Control of the Variance of TCR CDR-B3: Insights Gained From Germline Replacement of a TCR Dß Gene Segment With an Ig D H Gene Segment.

We have previously shown that the sequence of the immunoglobulin diversity gene segment (D H ) helps dictate the structure and composition of complementarity determining region 3 of the immunoglobulin heavy chain (CDR-H3). In order to test the role of germline D sequence on the diversity of the preimmune TCRß repertoire of T cells, we generated a mouse with a mutant TCRß DJC locus wherein the Dß2-Jß2 gene segment cluster was deleted and the remaining diversity gene segment, Dß1 (IMGT:TRDB1), was replaced with DSP2.3 (IMGT:IGHD2-02), a commonly used B cell immunoglobulin D H gene segment. Crystallographic studies have shown that the length and thus structure of TCR CDR-B3 places amino acids at the tip of CDR-B3 in a position to directly interact with peptide bound to an MHC molecule. The length distribution of complementarity determining region 3 of the T cell receptor beta chain (CDR-B3) has been proposed to be restricted largely by MHC-specific selection, disfavoring CDR-B3 that are too long or too short. Here we show that the mechanism of control of CDR-B3 length depends on the Dß sequence, which in turn dictates exonucleolytic nibbling. By contrast, the extent of N addition and the variance of created CDR3 lengths are regulated by the cell of origin, the thymocyte. We found that the sequence of the D and control of N addition collaborate to bias the distribution of CDR-B3 lengths in the pre-immune TCR repertoire and to focus the diversity provided by N addition and the sequence of the D on that portion of CDR-B3 that is most likely to interact with the peptide that is bound to the presenting MHC.

Mortality and Neurodevelopmental Outcomes in the Heart Rate Characteristics Monitoring Randomized Controlled Trial.

OBJECTIVE: To test whether the composite outcome of death or neurodevelopmental impairment (NDI) at 18-22 months corrected age for infants ≤1000 g at birth is decreased by continuous monitoring of heart rate characteristics during neonatal intensive care. STUDY DESIGN: We studied a subset of participants enrolled in a multicenter randomized trial of heart rate characteristics monitoring. Survivors were evaluated at 18-22 months corrected age with a standardized neurologic examination and the Bayley Scales of Infant Development-III (BSID-III). NDI was defined as Gross Motor Function Classification System of >2 (moderate or severe cerebral palsy), BSID-III language or cognitive scores of <70, severe bilateral hearing impairment, and/or bilateral blindness. RESULTS: The composite outcome, death or NDI, was obtained for 628 of 884 study infants (72%). The prevalence of this outcome was 44.4% (136/306) among controls (infants randomized to heart rate characteristics monitored but not displayed) and 38.9% (125/322) among infants randomized to heart rate characteristics monitoring displayed (relative risk, 0.87; 95% CI, 0.73-1.05; P = .17). Mortality was reduced from 32.0% (99/307) among controls to 24.8% (81/326) among monitoring displayed infants (relative risk, 0.75; 95% CI, 0.59 to 0.97; P = .028). The composite outcomes of death or severe CP and death or mildly low Bayley cognitive score occurred less frequently in the displayed group (P < .05). CONCLUSIONS: We found no difference in the composite outcome of death or NDI for extremely preterm infants whose heart rate characteristics were and were not displayed during neonatal intensive care. Two outcomes that included mortality or a specific NDI were less frequent in the displayed group.

A neonatal nonhuman primate model of gestational Zika virus infection with evidence of microencephaly, seizures and cardiomyopathy.

Zika virus infection during pregnancy is associated with miscarriage and with a broad spectrum of fetal and neonatal developmental abnormalities collectively known as congenital Zika syndrome (CZS). Symptomology of CZS includes malformations of the brain and skull, neurodevelopmental delay, seizures, joint contractures, hearing loss and visual impairment. Previous studies of Zika virus in pregnant rhesus macaques (Macaca mulatta) have described injury to the developing fetus and pregnancy loss, but neonatal outcomes following fetal Zika virus exposure have yet to be characterized in nonhuman primates. Herein we describe the presentation of rhesus macaque neonates with a spectrum of clinical outcomes, including one infant with CZS-like symptoms including cardiomyopathy, motor delay and seizure activity following maternal infection with Zika virus during the first trimester of pregnancy. Further characterization of this neonatal nonhuman primate model of gestational Zika virus infection will provide opportunities to evaluate the efficacy of pre- and postnatal therapeutics for gestational Zika virus infection and CZS.

The Effect of Extended Continuous Positive Airway Pressure on Changes in Lung Volumes in Stable Premature Infants: A Randomized Controlled Trial.

OBJECTIVE: To compare changes in lung volumes, as measured by functional residual capacity (FRC), through to discharge in stable infants randomized to 2 weeks of extended continuous positive airway pressure CPAP (eCPAP) vs CPAP discontinuation (dCPAP). STUDY DESIGN: Infants born at ≤32 weeks of gestation requiring ≥24 hours of CPAP were randomized to 2 weeks of eCPAP vs dCPAP when meeting CPAP stability criteria. FRC was measured with the nitrogen washout technique. Infants were stratified by gestational age (<28 and ≥ 28 weeks) and twin gestation. A linear mixed-effects model was used to evaluate the change in FRC between the 2 groups. Data were analyzed blinded to treatment group allocation. RESULTS: Fifty infants were randomized with 6 excluded, for a total of 44 infants. Baseline characteristics were similar in the 2 groups. The infants randomized to eCPAP vs dCPAP had a greater increase in FRC from randomization through 2 weeks (12.6 mL vs 6.4 mL; adjusted 95% CI, 0.78-13.47; P = .03) and from randomization through discharge (27.2 mL vs 17.1 mL; adjusted 95% CI, 2.61-17.59; P = .01). CONCLUSIONS: Premature infants randomized to eCPAP had a significantly greater increase in FRC through discharge compared with those randomized to dCPAP. An increased change in FRC may lead to improved respiratory health. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02249143.

Meningitis, urinary tract, and bloodstream infections in very low birth weight infants enrolled in a heart rate characteristics monitoring trial.

BACKGROUND: Displaying heart rate characteristic (HRC) scores was associated with lower sepsis-associated mortality in very low birth weight (VLBW) infants in a multicenter randomized controlled trial (HeRO trial). The aim of this study was to test whether HRC indices rise before diagnosis of urinary tract infection (UTI) or meningitis, with and without concomitant BSI. METHODS: Blood, urine, and cerebrospinal fluid (CSF) culture data after 3 days of age and within 120 days of study enrollment were analyzed from 2989 VLBW infants. The HRC index was analyzed 12 h prior to positive cultures compared to 36 h prior, using paired signed-rank tests. RESULTS: UTI, meningitis, and BSI were diagnosed in 10%, 2%, and 24% of infants, respectively. The mean hourly HRC index was significantly higher 12 h prior to diagnosis of UTI and BSI compared to 36 h prior (UTI 2.07 versus 1.81; BSI 2.62 versus 2.25, both p < 0.0001). The baseline HRC index was higher for meningitis, compared to UTI or BSI, but without a statistically significant rise in the day prior to meningitis diagnosis. CONCLUSIONS: In a large cohort of VLBW infants enrolled in the HeRO trial, the HRC index increased in the 24-h period prior to diagnosis of UTI and BSI but not meningitis.

Neonatal Intensive Care Unit Length of Stay Reduction by Heart Rate Characteristics Monitoring.

OBJECTIVE: To examine the effect of heart rate characteristics (HRC) monitoring on length of stay among very low birth weight (VLBW; <1500 g birth weight) neonates in the HeRO randomized controlled trial (RCT). STUDY DESIGN: We performed a retrospective analysis of length of stay metrics among 3 subpopulations (all patients, all survivors, and survivors with positive blood or urine cultures) enrolled in a multicenter, RCT of HRC monitoring. RESULTS: Among all patients in the RCT, infants randomized to receive HRC monitoring were more likely than controls to be discharged alive and prior to day 120 (83.6% vs 80.1%, P = .014). The postmenstrual age at discharge for survivors with positive blood or urine cultures was 3.2 days lower among infants randomized to receive HRC monitoring when compared with controls (P = .026). Although there were trends in other metrics toward reduced length of stay in HRC-monitored patients, none reached statistical significance. CONCLUSIONS: HRC monitoring is associated with reduced mortality in VLBW patients and a reduction in length of stay among infected surviving VLBW infants. TRIAL REGISTRATION: ClinicalTrials.gov: NCT00307333.

Beyond the uterine environment: a nonhuman primate model to investigate maternal-fetal and neonatal outcomes following chronic intrauterine infection.

BackgroundIntrauterine infection is a significant cause of early preterm birth. We have developed a fetal-neonatal model in the rhesus macaque to determine the impact of chronic intrauterine infection with Ureaplasma parvum on early neonatal reflexes and brain development.MethodsTime-mated, pregnant rhesus macaques were randomized to be inoculated with U. parvum (serovar 1; 105 c.f.u.) or control media at ~120 days' gestational age (dGA). Neonates were delivered by elective hysterotomy at 135-147 dGA (term=167d), stabilized, and cared for in our nonhuman primate neonatal intensive care unit. Neonatal reflex behaviors were assessed from birth, and fetal and postnatal brain magnetic resonance imaging (MRI) was performed.ResultsA total of 13 preterm and 5 term macaque infants were included in the study. Ten preterm infants survived to 6 months of age. U. parvum-infected preterm neonates required more intensive respiratory support than did control infants. MRI studies suggested a potential perturbation of brain growth and white matter maturation with exposure to intra-amniotic infection.ConclusionWe have demonstrated the feasibility of longitudinal fetal-neonatal studies in the preterm rhesus macaque after chronic intrauterine infection. Future studies will examine long-term neurobehavioral outcomes, cognitive development, neuropathology, and in vivo brain imaging to determine the safety of antenatal antibiotic treatment for intrauterine infection.

Alterations in B cell development, CDR-H3 repertoire and dsDNA-binding antibody production among C57BL/6 ΔD-iD mice congenic for the lupus susceptibility loci sle1, sle2 or sle3.

Systemic lupus erythematosus (SLE) is an autoimmune disease that reflects a failure to block the production of self-reactive antibodies, especially those that bind double-stranded DNA (dsDNA). Backcrossing the lupus-prone NZM2410 genome onto C57BL/6 led to the identification of three genomic intervals, termed sle1, sle2 and sle3, which are associated with lupus susceptibility. We previously generated a C57BL/6 strain congenic for an immunoglobulin DH locus (ΔD-iD) that enriches for arginine at dsDNA-binding positions. We individually introduced the ΔD-iD allele into the three sle strains to test whether one or more of these susceptibility loci could affect the developmental fate of B cells bearing arginine-enriched CDR-H3s, the CDR-H3 repertoire created by the DH and the prevalence of dsDNA-binding antibodies. We found that the combination of the ΔD-iD allele and the sle1 locus led to a decrease in mature, recirculating B cell numbers and an increase in marginal zone cell numbers while maintaining a highly charged CDR-H3 repertoire. ΔD-iD and sle2 had no effect on peripheral B cell numbers, but the CDR-H3 repertoire was partially normalized. ΔD-iD and sle3 led to an increase in marginal zone B cell numbers, with some normalization of hydrophobicity. Mice with ΔD-iD combined with either sle1 or sle3 had increased production of dsDNA-binding IgM and IgG by 12 months of age. These findings indicate that the peripheral CDR-H3 repertoire can be categorically manipulated by the effects of nonimmunoglobulin genes.

Violation of an evolutionarily conserved immunoglobulin diversity gene sequence preference promotes production of dsDNA-specific IgG antibodies.

Variability in the developing antibody repertoire is focused on the third complementarity determining region of the H chain (CDR-H3), which lies at the center of the antigen binding site where it often plays a decisive role in antigen binding. The power of VDJ recombination and N nucleotide addition has led to the common conception that the sequence of CDR-H3 is unrestricted in its variability and random in its composition. Under this view, the immune response is solely controlled by somatic positive and negative clonal selection mechanisms that act on individual B cells to promote production of protective antibodies and prevent the production of self-reactive antibodies. This concept of a repertoire of random antigen binding sites is inconsistent with the observation that diversity (DH) gene segment sequence content by reading frame (RF) is evolutionarily conserved, creating biases in the prevalence and distribution of individual amino acids in CDR-H3. For example, arginine, which is often found in the CDR-H3 of dsDNA binding autoantibodies, is under-represented in the commonly used DH RFs rearranged by deletion, but is a frequent component of rarely used inverted RF1 (iRF1), which is rearranged by inversion. To determine the effect of altering this germline bias in DH gene segment sequence on autoantibody production, we generated mice that by genetic manipulation are forced to utilize an iRF1 sequence encoding two arginines. Over a one year period we collected serial serum samples from these unimmunized, specific pathogen-free mice and found that more than one-fifth of them contained elevated levels of dsDNA-binding IgG, but not IgM; whereas mice with a wild type DH sequence did not. Thus, germline bias against the use of arginine enriched DH sequence helps to reduce the likelihood of producing self-reactive antibodies.

Cytokines associated with necrotizing enterocolitis in extremely-low-birth-weight infants.

BACKGROUND: The goal was to identify cytokines associated with necrotizing enterocolitis (NEC). Based on our earlier reports of decreased tissue expression of transforming growth factor (TGF)-ß, we hypothesized that infants with NEC also have low blood TGF-ß levels. We further hypothesized that because fetal inflammation increases the risk of NEC, infants who develop NEC have elevated blood cytokine levels in early neonatal period. METHODS: Data on 104 extremely-low-birth-weight infants with NEC and 893 without NEC from 17 centers were analyzed. Clinical information was correlated with blood cytokine levels on postnatal day 1 (D1), D3, D7, D14, and D21. RESULTS: Male gender, non-Caucasian/non-African American ethnicity, sepsis, lower blood TGF-ß and interleukin (IL)-2 levels, and higher IL-8 levels were associated with NEC. The NEC group had lower TGF-ß levels than controls since D1. The diagnosis of NEC was associated with elevated IL-1ß, IL-6, IL-8, IL-10, monocyte chemoattractant protein-1/CC-motif ligand-2, macrophage inflammatory protein-1ß/CC-motif ligand-3, and C-reactive protein. CONCLUSION: Clinical characteristics, such as gender and ethnicity, and low blood TGF-ß levels are associated with higher risk of NEC. Infants who developed NEC did not start with high blood levels of inflammatory cytokines, but these rose mainly after the onset of NEC.

Septicemia mortality reduction in neonates in a heart rate characteristics monitoring trial.

BACKGROUND: Abnormal heart rate characteristics (HRC) wax and wane in early stages of culture-positive, late-onset septicemia (LOS) in patients in the neonatal intensive care unit (NICU). Continuously monitoring an HRC index leads to a reduction in mortality among very low birth weight (VLBW) infants. We hypothesized that the reduction in mortality was due to a decrease in septicemia-associated mortality. METHODS: This is a secondary analysis of clinical and HRC data from 2,989 VLBW infants enrolled in a randomized clinical trial of HRC monitoring in nine NICUs from 2004 to 2010. RESULTS: LOS was diagnosed 974 times in 700 patients, and the incidence and distribution of organisms were similar in HRC display and nondisplay groups. Mortality within 30 d of LOS was lower in the HRC display as compared with the nondisplay group (11.8 vs. 19.6%; relative risk: 0.61; 95% confidence interval: 0.43, 0.87; P < 0.01), but mortality reduction was not statistically significant for patients without LOS. There were fewer large, abrupt increases in the HRC index in the days leading up to LOS diagnosis in infants whose HRC index was displayed. CONCLUSION: Continuous HRC monitoring is associated with a lower septicemia-associated mortality in VLBW infants, possibly due to diagnosis earlier in the course of illness.

Recirculating bone marrow B cells in C57BL/6 mice are more tolerant of highly hydrophobic and highly charged CDR-H3s than those in BALB/c mice.

To test whether mechanisms controlling the range of diversity of the developing antibody repertoire in C57BL/6 mice (IgH(b)) operate similarly to those identified in BALB/c mice (IgH(a)), we compared the sequences of VH 7183-containing H-chain transcripts from sorted adult bone marrow C57BL/6 B-cell subsets with those previously obtained from BALB/c mice. Patterns of VDJ gene segment utilization and CDR-H3 amino acid composition, charge, and average length in C57BL/6 pro-B cells were similar, although not identical, to BALB/c pro-B cells. However, C57BL/6 mature, recirculating B cells failed to demonstrate the reduction in the use of VH81X and the narrowing in the range of variance of CDR-H3 hydrophobicity that characterizes B-cell maturation in BALB/c mice. To further test the ability of the C57BL/6 strain to discard B cells expressing highly charged CDR-H3s, we introduced a mutant IgH(a) DH allele that forces use of arginine, asparagine, and histidine. Unlike BALB/c mice, C57BL/6 mice congenic for the charged DH maintained normal numbers of mature, recirculating B cells that were enriched for charged CDR-H3s. Together these findings indicate that the mature C57BL/6 B-cell pool permits expression of immunoglobulins with antigen-binding sites that are typically discarded during late-stage bone marrow B-cell development in BALB/c mice.

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.