Population pharmacokinetics and target attainment analyses to identify a rational empirical dosing strategy for cefepime in critically ill patients.

OBJECTIVES: We aimed to identify rational empirical dosing strategies for cefepime treatment in critically ill patients by utilizing population pharmacokinetics and target attainment analysis. PATIENTS AND METHODS: A prospective and opportunistic pharmacokinetic (PK) study was conducted in 130 critically ill patients in two ICU sites. The plasma concentrations of cefepime were determined using a validated LC-MS/MS method. All cefepime PK data were analysed simultaneously using the non-linear mixed-effects modelling approach. Monte Carlo simulations were performed to evaluate the PTA of cefepime at different MIC values following different dose regimens in subjects with different renal functions. RESULTS: The PK of cefepime in critically ill patients was best characterized by a two-compartment model with zero-order input and first-order elimination. Creatinine clearance and body weight were identified to be significant covariates. Our simulation results showed that prolonged 3 h infusion does not provide significant improvement on target attainment compared with the traditional intermittent 0.5 h infusion. In contrast, for a given daily dose continuous infusion provided much higher breakpoint coverage than either 0.5 h or 3 h intermittent infusions. To balance the target attainment and potential neurotoxicity, cefepime 3 g/day continuous infusion appears to be a better dosing regimen than 6 g/day continuous infusion. CONCLUSIONS: Continuous infusion may represent a promising strategy for cefepime treatment in critically ill patients. With the availability of institution- and/or unit-specific cefepime susceptibility patterns as well as individual patients' renal function, our PTA results may represent useful references for physicians to make dosing decisions.

Evaluation of Empirical Dosing Regimens for Meropenem in Intensive Care Unit Patients Using Population Pharmacokinetic Modeling and Target Attainment Analysis.

In the present study, population pharmacokinetic (PK) analysis was performed based on meropenem data from a prospective study conducted in 114 critically ill patients with a wide range of renal functions and various disease conditions. The final model was a one-compartment model with linear elimination, with creatinine clearance and continuous renal replacement therapy affecting clearance, and total bodyweight impacting the volume of distribution. Our model is a valuable addition to the existing meropenem population PK models, and it could be particularly useful during implementation of a therapeutic drug monitoring program combined with Bayesian forecasting. Based on the final model developed, comprehensive Monte Carlo simulations were performed to evaluate the probability of target attainment (PTA) of 16 different dosing regimens. Simulation results showed that 2 g administered every 8 h with 3-h prolonged infusion (PI) and 4 g/day by continuous infusion (CI) appear to be two empirical dosing regimens that are superior to many other regimens when both target attainment and potential toxicity are considered and renal function information is not available. Following a daily CI dose of 6 g or higher, more than 30% of the population with a creatinine clearance of <60 mL/min is predicted to have neurotoxicity. With the availability of institution- and/or unit-specific meropenem susceptibility patterns, as well as an individual patient's renal function, our PTA results may represent useful references for physicians to make dosing decisions.

Antibodies against biotin-labeled red blood cells can shorten posttransfusion survival.

BACKGROUND: In hematologic and transfusion medicine research, measurement of red blood cell (RBC) in vivo kinetics must be safe and accurate. Recent reports indicate use of biotin-labeled RBC (BioRBC) to determine red cell survival (RCS) offers substantial advantages over 51 Cr and other labeling methods. Occasional induction of BioRBC antibodies has been reported. STUDY DESIGN AND METHODS: To investigate the causes and consequences of BioRBC immunization, we reexposed three previously immunized adults to BioRBC and evaluated the safety, antibody emergence, and RCS of BioRBC. RESULTS: BioRBC re-exposure caused an anamnestic increase of plasma BioRBC antibodies at 5-7 days; all were subclass IgG1 and neutralized by biotinylated albumin, thus indicating structural specificity for the biotin epitope. Concurrently, specific antibody binding to BioRBC was observed in each subject. As biotin label density increased, the proportion of BioRBC that bound increased antibody also increased; the latter was associated with proportional accelerated removal of BioRBC labeled at density 6 µg/mL. In contrast, only one of three subjects exhibited accelerated removal of BioRBC density 2 µg/mL. No adverse clinical or laboratory events were observed. Among three control subjects who did not develop BioRBC antibodies following initial BioRBC exposure, re-exposure induced neither antibody emergence nor accelerated BioRBC removal. DISCUSSION: We conclude re-exposure of immunized subjects to BioRBC can induce anamnestic antibody response that can cause an underestimation of RCS. To minimize chances of antibody induction and underestimation of RCS, we recommend an initial BioRBC exposure volume of ≤10 mL and label densities of ≤18 µg/mL.

Development and validation of a simple and sensitive LC-MS/MS method for the quantification of cefazolin in human plasma and its application to a clinical pharmacokinetic study.

Cefazolin is widely used during surgery to prevent surgical site infections (SSIs). Although cefazolin redosing is often needed due to its short half-life, the appropriate redosing schedule remains controversial and there is limited information on cefazolin disposition following repeated doses during surgery. In parallel with an ongoing cefazolin redosing clinical study, we have developed and fully validated a simple and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of cefazolin in human plasma. A simple protein precipitation was used for sample preparation. MS/MS analysis was performed using multiple reaction monitoring (MRM) under a positive ionization mode. The lower limit of quantification (LLOQ) for cefazolin was evaluated at 0.25 µg/mL and a linearity ranging from 0.25 to 300 µg/mL. Accuracy was ≤ 114.3% for quality controls and ≤ 118.2% for LLOQ; intra-day and inter-day precision ranging from 1.9% to 14.2% for all quality controls and LLOQ. Matrix effect, extraction recovery, stability testing, dilution integrity, hemolysis effects and whole blood stability have all been investigated. A total of 17 parameters were validated and passed their validation criteria. The method was applied in the quantification of cefazolin in clinical plasma samples and was able to successfully determine the concentrations in patients undergoing various surgeries. In comparison with other prior published methods, our method has a simple sample preparation combined with a short analysis run time, a wide dynamic range and low limit of quantification, and is a fully validated assay that abides by FDA guidance.

Sex-specific cytokine responses and neurocognitive outcome after blood transfusions in preterm infants.

BACKGROUND: The objective of this study was to determine sex-specific differences in inflammatory cytokine responses to red blood cell (RBC) transfusion in preterm infants in the neonatal period and their relationship to later neurocognitive status. METHODS: Infants with a birth weight <1000 g and gestational age 22-29 weeks were enrolled in the Transfusion of Prematures (TOP) trial. The total number of transfusions was used as a marker of transfusion status. Nineteen cytokines and biomarkers were analyzed from 71 infants longitudinally during the neonatal period. Twenty-six infants completed the Bayley Scales of Infant & Toddler Development, 3rd Edition (Bayley-III) at 12 months' corrected age. RESULTS: Nine cytokine levels were significantly elevated in proportion to the number of transfusions received. Of those, one cytokine showed a sex-specific finding (p = 0.004): monocyte chemoattractant protein-1, MCP-1, rose substantially in females (8.9% change per additional transfusion), but not in males (-0.8% change). Higher concentrations of MCP-1 exclusively were associated with worse Bayley-III scores: decreased cognitive raw scores (p = 0.0005) and motor scaled scores (p < 0.0001). CONCLUSIONS: This study provides evidence of a sex-specific difference in the inflammatory response to RBC transfusions during neonatal life, with MCP-1 levels rising only in females and inversely correlating with neurocognitive status at 12 months old. IMPACT: It is important to understand the risk factors for abnormal neurodevelopment in preterm infants, including anemia and RBC transfusion, in order to improve outcomes and provide potential targets for therapy. Our study investigates and provides the first evidence of sex-specific differences in inflammatory cytokine responses to RBC transfusions in preterm infants in the neonatal period, and their relationship to later cognitive outcomes. This study critically suggests that different transfusion thresholds may have a sex-specific effect on neurodevelopment: females have worse cognitive outcomes with increased number of transfusions, while males have worse outcomes with lower number of transfusions.

Development and validation of a simple and sensitive LC-MS/MS method for quantification of ampicillin and sulbactam in human plasma and its application to a clinical pharmacokinetic study.

Ampicillin-sulbactam is a broad-spectrum combination antibiotic used for a variety of clinical applications, including as a prophylactic agent to reduce the risk of surgical site infection. The pharmacokinetics of ampicillin-sulbactam after redosing during prolonged surgeries remains incompletely understood. In anticipation of further studying the intra-operative pharmacokinetics of this drug, we have developed a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of ampicillin and sulbactam. The plasma samples were prepared using a simple protein precipitation method. Gradient chromatographic elution was used to separate analytes, and MS/MS analysis was performed in negative ionization mode for both analytes via multiple reaction monitoring (MRM). All validation parameters were evaluated under a good laboratory practice (GLP) environment. For both ampicillin and sulbactam, the lower limit of quantitation (LLOQ) was established as 0.25 µg/mL. The calibration curve ranged from 0.25 to 200 µg/mL for ampicillin and 0.25-100 µg/mL for sulbactam. Inter- and intra-day precisions for both analytes were ≤11.5 % for quality controls and ≤17.4 % for LLOQ; accuracies ranged from -11.5 to 12.5% for 3 quality control levels and -18.1-18.7% for LLOQ. In addition to sensitivity, accuracy and precision, 13 other parameters were also validated for both analytes, and the results met the acceptance criteria. Our method was successfully applied to quantify ampicillin and sulbactam concentrations in patients undergoing surgery.

Neonatal Umbilical Arterial Catheter Removal Is Accompanied by a Marked Decline in Phlebotomy Blood Loss.

BACKGROUND: Umbilical arterial catheters (UACs) are frequently used in critically ill neonates. UAC are convenient, reliable, and allow for caregiver convenience in performing painless arterial blood sampling. We hypothesized that UAC removal in extremely low birth weight (ELBW) neonates will result in significantly less phlebotomy blood loss (PBL) after correcting for severity of illness. STUDY DESIGN AND METHODS: PBL was measured at a single center in 99 ELBW infants who survived to day 28. Individual infant's paired daily PBL for the two 24-h periods before and after UAC removal were compared using the paired t test. Daily PBL up to 7 days before and 7 days after UAC removal were compared using a logistic regression with mixed model analysis for repeated measures. Cumulative 28-day phlebotomy loss was evaluated by multiple linear regression analysis. RESULTS: PBL 24 h before and after UAC removal were 1.7 mL (95% CI 1.5-1.9) and 0.9 mL (95% CI 0.8-1.0; p < 0.0001), respectively. Cumulative 28-day PBL increased by 2.2 mL (±0.7) per day that a UAC was present with or without correction for severity of illness (p < 0.001). CONCLUSION: UAC removal is independently associated with a marked decline in PBL. We speculate the ease and convenience of UAC blood sampling lead to more frequent blood testing and greater PBL.

Aspects of matrix and analyte effects in clinical pharmacokinetic sample analyses using LC-ESI/MS/MS - Two case examples.

The increasing focus on high throughput sample analysis has led to the common practice of using simplest sample preparation method possible (i.e. protein precipitation) and shortest sample run-time possible. This means that there will be two aspects of compromise: the first compromise is made between sample cleanliness and sample preparation speed since protein precipitation does not provide very clean final extract; the second compromise is made between peak separation and run-time, meaning that sometimes overlap or co-elution of some peaks has to be accepted. The first compromise may lead to matrix effect, which is caused by co-eluting endogenous substances such as phospholipids. The second compromise can result in analyte effect, which is caused by co-eluting analyte(s). We have encountered the issue of matrix/analyte-mediated ion suppression in multiple preclinical and clinical pharmacokinetic projects during bioanalytical method development/validation or biological sample analysis of many small molecule drugs. As these matrix/analyte effects could occur in different situations with different "syndromes", sometimes it can be easily overlooked, leading to unreliable result, poor sensitivity, and prolonged assay development process. To increase the awareness of this important issue, in this paper we presented two real case examples on signal suppression caused by either endogenous phospholipids or co-eluting analyte.

Anemia induces gut inflammation and injury in an animal model of preterm infants.

BACKGROUND: While very low birth weight (VLBW) infants often require multiple red blood cell transfusions, efforts to minimize transfusion-associated risks have resulted in more restrictive neonatal transfusion practices. However, whether restrictive transfusion strategies limit transfusions without increasing morbidity and mortality in this population remains unclear. Recent epidemiologic studies suggest that severe anemia may be an important risk factor for the development of necrotizing enterocolitis (NEC). However, the mechanism whereby anemia may lead to NEC remains unknown. STUDY DESIGN AND METHODS: The potential impact of anemia on neonatal inflammation and intestinal barrier disruption, two well-characterized predisposing features of NEC, was defined by correlation of hemoglobin values to cytokine levels in premature infants and by direct evaluation of intestinal hypoxia, inflammation and gut barrier disruption using a pre-clinical neonatal murine model of phlebotomy-induced anemia (PIA). RESULTS: Increasing severity of anemia in the preterm infant correlated with the level of IFN-gamma, a key pro-inflammatory cytokine that may predispose an infant to NEC. Gradual induction of PIA in a pre-clinical model resulted in significant hypoxia throughout the intestinal mucosa, including areas where intestinal macrophages reside. PIA-induced hypoxia significantly increased macrophage pro-inflammatory cytokine levels, while reducing tight junction protein ZO-1 expression and increasing intestinal barrier permeability. Macrophage depletion reversed the impact of anemia on intestinal ZO-1 expression and barrier function. CONCLUSIONS: Taken together, these results suggest that anemia can increase intestinal inflammation and barrier disruption likely through altered macrophage function, leading to the type of predisposing intestinal injury that may increase the risk for NEC.

Quantification of Cefepime, Meropenem, Piperacillin, and Tazobactam in Human Plasma Using a Sensitive and Robust Liquid Chromatography-Tandem Mass Spectrometry Method, Part 2: Stability Evaluation.

Although the stability of ß-lactam antibiotics is a known issue, none of the previously reported bioanalytical methods had an adequate evaluation of the stability of these drugs. In the current study, the stability of cefepime, meropenem, piperacillin, and tazobactam under various conditions was comprehensively evaluated. The evaluated parameters included stock solution stability, short-term stability, long-term stability, freeze-thaw stability, processed sample stability, and whole-blood stability. When stored at -20°C, the stock solution of meropenem in methanol was stable for up to 3 weeks, and the stock solutions of cefepime, piperacillin, and tazobactam were stable for up to 6 weeks. All four antibiotics were stable in human plasma for up to 3 months when stored at -80°C and were stable in whole blood for up to 4 h at room temperature. Short-term stability results indicated that all four ß-lactams were stable at room temperature for 2 h, but substantial degradation was observed when the plasma samples were stored at room temperature for 24 h, with the degradation rates for cefepime, meropenem, piperacillin, and tazobactam being 30.1%, 75.6%, 49.0%, and 37.7%, respectively. Because the stability information is method independent, our stability results can be used as a reference by other research groups that work with these antibiotics.

Quantification of Cefepime, Meropenem, Piperacillin, and Tazobactam in Human Plasma Using a Sensitive and Robust Liquid Chromatography-Tandem Mass Spectrometry Method, Part 1: Assay Development and Validation.

The highly variable pharmacokinetics of ß-lactam antibiotics and ß-lactamase inhibitors poses a significant challenge to clinicians in ensuring appropriate antibiotic doses in critically ill patients. Therefore, routine monitoring of plasma concentrations is important for individualization of antimicrobial therapy. Accordingly, a simple and robust analytical method for the simultaneous measurement of multiple ß-lactam antibiotics and ß-lactamase inhibitors is highly desirable to ensure quick decisions on dose adjustments. In this study, a sensitive, simple, and robust method for the simultaneous quantification of cefepime, meropenem, piperacillin, and tazobactam in human plasma was developed and rigorously validated according to FDA guidance. Sample extraction was accomplished by simple protein precipitation. Chromatographic separation of analytes was achieved using stepwise gradient elution. Analytes were monitored using tandem mass spectrometry (MS/MS) with a turbo ion spray source in positive multiple-reaction-monitoring mode. The calibration curve ranged from 0.5 to 150 µg/ml for cefepime, 0.1 to 150 µg/ml for meropenem and piperacillin, and 0.25 to 150 µg/ml for tazobactam. Inter- and intraday precision and accuracy, sensitivity, selectivity, dilution integrity, matrix effect, extraction recovery, and hemolysis effect were investigated for all four analytes, and the results met the acceptance criteria. Compared to other reported methods, our method is more robust because of the combination of the following features: (i) a simple sample extraction procedure, (ii) a short sample run time, (iii) a wide dynamic range, and (iv) the small plasma sample volume needed. Since our method already covers ß-lactams and a ß-lactamase inhibitor with highly heterogeneous physicochemical properties, further antibiotic candidates may easily be incorporated into this multianalyte method.

Development, validation, and potential applications of biotinylated red blood cells for posttransfusion kinetics and other physiological studies: evidenced-based analysis and recommendations.

The current reference method in the United States for measuring in vivo population red blood cell (RBC) kinetics utilizes chromium-51 (51 Cr) RBC labeling for determining RBC volume, 24-hour posttransfusion RBC recovery, and long-term RBC survival. Here we provide evidence supporting adoption of a method for kinetics that uses the biotin-labeled RBCs (BioRBCs) as a superior, versatile method for both regulatory and investigational purposes. RBC kinetic analysis using BioRBCs has important methodologic, analytical, and safety advantages over 51 Cr-labeled RBCs. We critically review recent advances in labeling human RBCs at multiple and progressively lower biotin label densities for concurrent, accurate, and sensitive determination of both autologous and allogeneic RBC population kinetics. BioRBC methods valid for RBC kinetic studies, including successful variations used by the authors, are presented along with pharmacokinetic modeling approaches for the accurate determination of RBC pharmacokinetic variables in health and disease. The advantages and limitations of the BioRBC method-including its capability of determining multiple BioRBC densities simultaneously in the same individual throughout the entire RBC life span-are presented and compared with the 51 Cr method. Finally, potential applications and limitations of kinetic BioRBC determinations are discussed.

In premature infants there is no decrease in 24-hour posttransfusion allogeneic red blood cell recovery after 42 days of storage.

BACKGROUND: Critically ill preterm very-low-birthweight (VLBW) neonates (birthweight ≤ 1.5 kg) frequently develop anemia that is treated with red blood cell (RBC) transfusions. Although RBCs transfused to adults demonstrate progressive decreases in posttransfusion 24-hour RBC recovery (PTR24 ) during storage-to a mean of approximately 85% of the Food and Drug Administration-allowed 42-day storage-limited data in infants indicate no decrease in PTR24 with storage. STUDY DESIGN AND METHODS: We hypothesized that PTR24 of allogeneic RBCs transfused to anemic VLBW newborns: 1) will be greater than PTR24 of autologous RBCs transfused into healthy adults and 2) will not decrease with increasing storage duration. RBCs were stored at 4°C for not more than 42 days in AS-3 or AS-5. PTR24 was determined in 46 VLBW neonates using biotin-labeled RBCs and in 76 healthy adults using 51 Cr-labeled RBCs. Linear mixed-model analysis was used to estimate slopes and intercepts of PTR24 versus duration of RBC storage. RESULTS: For VLBW newborns, the estimated slope of PTR24 versus storage did not decrease with the duration of storage (p = 0.18) while for adults it did (p < 0.0001). These estimated slopes differed significantly in adults compared to newborns (p = 0.04). At the allowed 42-day storage limit, projected mean neonatal PTR24 was 95.9%; for adults, it was 83.8% (p = 0.0002). CONCLUSIONS: These data provide evidence that storage duration of allogeneic RBCs intended for neonates can be increased without affecting PTR24 . This conclusion supports the practice of transfusing RBCs stored up to 42 days for small-volume neonatal transfusions to limit donor exposure.

Antibodies to biotinylated red blood cells in adults and infants: improved detection, partial characterization, and dependence on red blood cell-biotin dose.

BACKGROUND: Biotin-labeled red blood cells (BioRBCs) are used for in vivo kinetic studies. Because BioRBC dosing occasionally induces antibodies, a sensitive and specific anti-BioRBC detection assay is needed. STUDY DESIGN AND METHODS: Aims were to 1) develop a gel card assay to evaluate existing, naturally occurring and BioRBC-induced plasma antibodies, 2) compare gel card and tube agglutination detection results, and 3) test for a relationship of antibody induction and BioRBC dose. Reagent BioRBCs were prepared using sulfo-NHS biotin ranging from densities 18 (BioRBC-18) to 1458 (BioRBC-1458) µg/mL RBCs. RESULTS: Among BioRBC-exposed subjects, gel card and tube agglutination results were concordant in 21 of 22 adults and all 19 infant plasma samples. Gel card antibody detection sensitivity was more than 10-fold greater than tube agglutination. Twelve to 16 weeks after BioRBC exposure, induced anti-antibodies were detected by gel card in three of 26 adults (12%) at reagent densities BioRBC-256 or less, but in none of 41 infants. Importantly, induced anti-BioRBC antibodies were associated with higher BioRBC dose (p = 0.008); no antibodies were detected in 18 subjects who received BioRBC doses less than or equal to BioRBC-18. For noninduced BioRBC antibodies, six of 1125 naïve adults (0.3%) and none of 46 naïve infants demonstrated existing anti-BioRBC antibodies using reagent BioRBC-140 or -162. Existing anti-BioRBCs were all neutralized by biotin compounds, while induced antibodies were not. CONCLUSIONS: The gel card assay is more sensitive than the tube agglutination assay. We recommend reagent BioRBC-256 for identifying anti-BioRBCs. Use of a low total RBC biotin label dose (≤ BioRBC-18) may minimize antibody induction.

Estimation of adult and neonatal RBC lifespans in anemic neonates using RBCs labeled at several discrete biotin densities.

BACKGROUND: Prior conclusions that autologous neonatal red blood cells (RBC) have substantially shorter lifespans than allogeneic adult RBCs were not based on direct comparison of autologous neonatal vs. allogeneic adult RBCs performed concurrently in the same infant. Biotin labeling of autologous neonatal RBCs and allogeneic adult donor RBCs permits concurrent direct comparison of autologous vs. allogeneic RBC lifespan. METHODS: RBCs from 15 allogeneic adult donors and from 15 very-low-birth-weight (VLBW) neonates were labeled at separate biotin densities and transfused simultaneously into the 15 neonates. Two mathematical models that account for the RBC differences were employed to estimate lifespans for the two RBC populations. RESULTS: Mean ± SD lifespan for adult allogeneic RBC was 70.1 ± 19.1 d, which is substantially shorter than the 120 d lifespan of both autologous and adult allogeneic RBC in healthy adults. Mean ± SD lifespan for neonatal RBC was 54.2 ± 11.3 d, which is only about 30% shorter than that of the adult allogeneic RBCs. CONCLUSION: This study provides evidence that extrinsic environmental factors primarily determine RBC survival (e.g., small bore of the capillaries of neonates, rate of oxygenation/deoxygenation cycles) rather than factors intrinsic to RBC.

A Mass Balance-Based Semiparametric Approach to Evaluate Neonatal Erythropoiesis.

Postnatal hemoglobin (Hb) production in anemic preterm infants is determined by several factors including the endogenous erythropoietin levels, allogeneic RBC transfusions administered to treat anemia, and developmental age. As a result, their postnatal Hb production rate can vary considerably. This work introduces a novel Hb mass balance-based semiparametric approach that utilizes infant blood concentrations of Hb from the first 30 postnatal days to estimate the amount of Hb produced and the erythropoiesis rate in newborn infants. The proposed method has the advantage of not relying on specific structural pharmacodynamic model assumptions to describe the Hb production, but instead utilizes simple mass balance principles and nonparametric regression analysis. The developed method was applied to the Hb data from 79 critically ill anemic very low birth weight preterm infants to evaluate the dynamic changes in erythropoiesis during the first month of life and to determine the inter-subject variability in Hb production. The estimated mean (±SD) cumulative amount of Hb produced by the infants over the first month of life was 6.6 ± 3.4 g (mean body weight, 0.768 kg), and the mean estimated body weight-scaled Hb production rate over the same period was 0.23 ± 0.12 g/day/kg. A significant positive correlation was observed between infant gestational age and the mean body weight-scaled Hb production rate over the first month of life (P < 0.05). We conclude that the proposed mathematical approach and its implementation provide a flexible framework to evaluate postnatal erythropoiesis in newborn infants.

Reticulocyte Hemoglobin Content During the First Month of Life in Critically Ill Very Low Birth Weight Neonates Differs From Term Infants, Children, and Adults.

BACKGROUND: Reticulocyte hemoglobin content (RET-He)-an established indicator of iron status in children and adults-was determined in very low birth weight (VLBW) infants. METHODS: Longitudinal retrospective RET-He data in 26 VLBW neonates during the first month of age were compared with: (a) concurrent complete blood counts (CBCs), including hemoglobin (Hb) concentration, reticulocyte count, and immature reticulocyte fraction (IRF), and erythropoietin (EPO) levels; (b) clinical variables; and (c) RET-He data from the literature for term infants, children, and adults. RESULTS: RET-He within 24 hr following birth was 31.8 ± 1.1 pg (mean ± SEM). This was followed by an abrupt, significant decline to 28.3 ± 1.1 pg at 2-4 days, and to steady state levels of 28.4 ± 0.5 pg thereafter. The changes in RET-He were mirrored by changes in plasma EPO, reticulocyte count, and IRF, but not Hb. Steady state RET-He values after 4 days were significantly lower than RET-He values for term infants, children, and adults (31.6 ± 0.11, 32.0 ± 0.12, and 33.0 ± 0.13 pg, respectively). CONCLUSION: Although RET-He values in VLBW infant were lower than term infants, children, and adults, the significance and mechanism(s) responsible are unknown. The present VLBW infant data are relevant to investigations assessing hemoglobinization following treatment with recombinant human EPO (r-HuEPO) and/or iron.

Autologous Infant and Allogeneic Adult Red Cells Demonstrate Similar Concurrent Post-Transfusion Survival in Very Low Birth Weight Neonates.

OBJECTIVE: Based on the hypothesis that neonatal autologous red blood cell (RBC) survival (RCS) is substantially shorter than adult RBC, we concurrently tracked the survival of transfused biotin-labeled autologous neonatal and allogeneic adult RBC into ventilated, very low birth weight infants. STUDY DESIGN: RBC aliquots from the first clinically ordered, allogeneic adult RBC transfusion and from autologous infant blood were labeled at separate biotin densities (biotin-labeled RBC [BioRBC]) and transfused. Survival of these BioRBCs populations were concurrently followed over weeks by flow cytometric enumeration using leftover blood. Relative tracking of infant autologous and adult allogeneic BioRBC was analyzed by linear mixed modeling of batched weekly data. When possible, Kidd antigen (Jka and Jkb) mismatches between infant and donor RBCs were also used to track these 2 populations. RESULTS: Contrary to our hypothesis, concurrent tracking curves of RCS of neonatal and adult BioRBC in 15 study infants did not differ until week 7, after which neonatal RCS became shortened to 59%-79% of adult enumeration values for uncertain reasons. Analysis of mismatched Kidd antigen RBC showed similar results, thus, confirming that BioRBC tracking is not perturbed by biotin RBC labeling. CONCLUSIONS: This study illustrates the utility of multidensity BioRBC labeling for concurrent measurement of RCS of multiple RBC populations in vivo. The similar RCS results observed for neonatal and adult BioRBCs transfused into very low birth weight infants provides strong evidence that the circulatory environment of the newborn infant, not intrinsic infant-adult RBC differences, is the primary determinant of erythrocyte survival. TRIAL REGISTRATION: Clinicaltrials.gov: NCT00731588.

A Method to Evaluate Fetal Erythropoiesis from Postnatal Survival of Fetal RBCs.

Fetal RBCs are produced during a period of very rapid growth and stimulated erythropoiesis under hypoxic intrauterine conditions. Fetal RBC life span varies with gestational age (GA) and is shorter than that in healthy adults. Due to the special kinetic properties of life span-based survival of human RBCs, a mathematical model-based kinetic analysis of the survival of fetal RBCs shortly after birth provides a unique opportunity to "look backward in time" to evaluate fetal erythropoiesis. This work introduces a novel method that utilizes postnatal in vivo RBC survival data collected within 2 days after birth to study both nonsteady-state (non-SS) in utero RBC production and changing fetal RBC life span over time. The effect of changes in erythropoiesis rate and RBC life span and the effect of multiple postnatal phlebotomies on the RBC survival curves were investigated using model-based simulations. This mathematical model, which considers both changes in the rate of erythropoiesis and RBC life span and which accurately accounts for the confounding effect of multiple phlebotomies, was applied to survival curves for biotin-labeled RBCs from ten anemic very low birth weight preterm infants. The estimated mean fetal RBC production rate scaled by body weight was 1.07 × 10(7) RBCs/day g, and the mean RBC life span at birth was 52.1 days; these values are consistent with reported values. The in utero RBC life span increased at a rate of 0.51 days per day of gestation. We conclude that the proposed mathematical model and its implementation provide a flexible framework to study in utero non-SS fetal erythropoiesis in newborn infants.

Mean remaining life span: a new clinically relevant parameter to assess the quality of transfused red blood cells.

BACKGROUND: The quality of transfused red blood cells (RBCs) to treat anemia depends on its potential for oxygen delivery, governed by two properties: 1) initial posttransfusion recovery and 2) life span of initially surviving RBCs. The latter property is poorly evaluated by the traditional mean potential life span (MPL) or mean cell age (MA), because these parameters do not evaluate how long transfused RBCs remain in circulation. Furthermore, evaluation of MPL is based on two problematic assumptions regarding transfused RBCs: 1) they were produced at a constant steady-state rate and 2) they have similar storage life spans. STUDY DESIGN AND METHODS: This work introduces a new parameter, the mean remaining life span (MRL) to quantify transfused RBC survival (TRCS) and presents a simple algorithm for its evaluation. The MRL was calculated for four adult subjects with sickle cell disease and four adult diabetic and nondiabetic subjects using RBC survival data sets with existing TRCS parameters. RESULTS: The RBC survival curves in the sickle cell subjects were nonlinear with rapid decline in survival within the first 5 days. The MRL was approximately 4.6 days. Thus, the MRL was indicative of the survival of all transfused RBCs. For the diabetic and nondiabetic subjects, the RBC disappearance curves did not deviate substantially from a linear decline. Thus, the estimates for MRL ranging from 39 to 51 days are similar to the MA previously computed. CONCLUSION: MRL overcomes limitations of previously proposed TRCS parameters, is simpler to calculate, and is physiologically and clinically more appropriate.