Published online August 1, 2008
PEDIATRICS Vol. 122 No. 2 August 2008, pp. 383-391 (doi:10.1542/peds.2007-2711)
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ARTICLE

A Phase I/II Trial of High-Dose Erythropoietin in Extremely Low Birth Weight Infants: Pharmacokinetics and Safety

Sandra E. Juul, MD, PhDa, Ronald J. McPherson, PhDa, Larry A. Bauer, PharmDb, Kelly J. Ledbetter, BAa, Christine A. Gleason, MDa and Dennis E. Mayock, MDa

a Departments of Pediatrics
b Pharmacy and Laboratory Medicine, University of Washington, Seattle, Washington


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
OBJECTIVES. High-dose recombinant erythropoietin is neuroprotective in animal models of neonatal brain injury. Extremely low birth weight infants are at high risk for brain injury and neurodevelopmental problems and might benefit from recombinant erythropoietin. We designed a phase I/II trial to test the safety and determine the pharmacokinetics of high-dose recombinant erythropoietin in extremely low birth weight infants.

METHODS. In a prospective, dose-escalation, open-label trial, we compared 30 infants who were treated with high-dose recombinant erythropoietin with 30 concurrent control subjects. Eligible infants were <24 hours old, ≤1000 g birth weight, and ≤28 weeks of gestation and had an umbilical artery catheter in place. Each infant received 3 intravenous doses of 500, 1000, or 2500 U/kg at 24-hour intervals beginning on day 1 of age. Blood samples were collected at scheduled intervals to determine recombinant erythropoietin pharmacokinetics. Safety parameters were also evaluated. In the concurrent control group, only clinical data were collected.

RESULTS. Mean erythropoietin concentrations 30 minutes after recombinant erythropoietin infusion were 5973 ± 266, 12291 ± 403, and 34197 ± 1641 mU/mL after 500, 1000, or 2500 U/kg, respectively. High-dose recombinant erythropoietin followed nonlinear pharmacokinetics as a result of decreasing clearance from the lowest dosage (17.3 mL/hour per kg for 500 U/kg) to the highest dosage (8.2 mL/hour per kg for 2500 U/kg). Steady state was achieved within 24 to 48 hours. Both 1000 and 2500 U/kg recombinant erythropoietin produced peak serum erythropoietin concentrations that were comparable to neuroprotective concentrations that previously were seen in experimental animals. No excess adverse events occurred in the recombinant erythropoietin–treated infants compared with control infants.

CONCLUSIONS. Early high-dose recombinant erythropoietin is well tolerated by extremely low birth weight infants, causing no excess morbidity or mortality. Recombinant erythropoietin dosages of 1000 and 2500 U/kg achieved neuroprotective serum levels.

Key Words: neonate • preterm • neuroprotection

Abbreviations: ELBW—extremely low birth weight • ICH—intracranial hemorrhage • Epo—erythropoietin • rEpo—recombinant erythropoietin • ROP—retinopathy of prematurity • PVL—periventricular leukomalacia • PDA—patent ductus arteriosus • AUC—area under the curve • NEC—necrotizing enterocolitis • TAOC—total antioxidant capacity • t1/2—half-life • Epo-R—erythropoietin receptor • HSD—honestly significant differences

Since 1991, mortality rates for preterm infants <1000 g have improved significantly.1 Although more extremely low birth weight (ELBW) infants now survive, the proportion who sustain significant neurologic impairment remains relatively constant. Thus, the number of impaired survivors has actually increased.2–5 Neurodevelopmental impairment (neurosensory abnormality including cerebral palsy, deafness, blindness, and/or Mental Developmental Index score of <70) is present in 36% to 48% of survivors.4,6 ELBW infants are particularly vulnerable to brain injury during transition between intrauterine and extrauterine life, with >50% of intracranial hemorrhage (ICH) occurring by day 1 of life and >90% by day 4. Hypotension and respiratory distress, which tend to be most acute in the first days of life, may contribute to this early vulnerability.7 Furthermore, periventricular white matter injury, although not usually apparent on neuroimaging studies for several weeks, is believed to occur in the first few days of life. We propose that a safe, effective neuroprotective intervention that targets early brain injury might confer long-term benefit.

High-dose recombinant human erythropoietin (rEpo) decreases both short-term and long-term sequelae of brain injury in neonatal rodent models.8–11 Effective neuroprotective dosages used in neonatal animal models of hypoxia-ischemia range from 1000 to 30000 U/kg,8 and optimal protection is produced with 3 doses of 5000 U/kg given within 72 hours of injury.9 In neonatal rats, a single intraperitoneal dose of 5000 U/kg rEpo produces a peak plasma Epo concentration of ~10000 mU/mL, with corresponding brain tissue Epo concentrations of >3 mU/mg protein.12 The pharmacokinetics of high-dose rEpo in preterm infants have not been studied.

Known adverse effects of long-term rEpo treatment in adults include hypertension, seizures, thrombus formation, polycythemia, red cell aplasia secondary to anti-Epo antibodies, and death.13 Anemic neonates who are treated with low-dose rEpo do not experience the same complications that have been observed in adults, and many studies have shown such treatment to be quite safe.14 Differences between erythropoietic and neuroprotective rEpo regimens may result in different responses to treatment. Neuroprotection requires higher dosages, because <2% crosses the blood-brain barrier.15 Duration of therapy is also shorter, typically just 3 doses compared with a minimum of 2 weeks. Although erythropoietic dosages have been well evaluated for safety, to date, only 2 clinical trials have been published using high-dose rEpo neuroprotection regimens: 1 of adult patients who sustained a stroke16 and 1 of adult patients with schizophrenia.17 Both studies found high-dose rEpo to be safe and beneficial. Because preterm neonates are undergoing rapid development, specific concerns must be addressed. These include the possible effects of rEpo on iron use18 and on the development of retinopathy of prematurity (ROP).19

We hypothesized that high-dose rEpo treatment during the first 3 days of life will provide neuroprotection to ELBW infants and decrease both major and minor morbidities; however, before a definitive clinical trial can be designed to test the neuroprotective efficacy of neonatal high-dose rEpo administration, basic information on pharmacokinetics, safety, and associated effects is needed. Therefore, the primary goal of this study was to obtain pharmacokinetic data, and the secondary objective was to obtain preliminary safety data from ELBW infants who were given a neuroprotective regimen of high-dose rEpo for the first 3 days of life.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Study Design
This was a prospective, dose-escalation, open-label phase I/II study. Enrollment occurred from January 2006 through March 2007. A total of 60 patients were enrolled: 30 study patients and 30 concurrent control subjects. Study subjects (n = 10 per group) received 1 of 3 dosages of rEpo (500, 1000, or 2500 U/kg intravenously). Infants received 3 injections at 24-hour intervals beginning on day 1 of life. The lowest dosage was tested first, and dosages were increased by group after data safety monitoring board review and approval. This study was registered with the US Food and Drug Administration under the investigational device exemption approval program (IND 12656).

Patients were enrolled at the University of Washington Medical Center and Providence Everett Medical Center NICUs. Data were collected from admission until home discharge or transfer to another hospital for convalescing. When infants were transferred to the Children's Hospital Regional Medical Care NICU for surgical evaluation or treatment, data from that hospital stay were included as part of this study. University of Washington neonatologists staff all 3 units. The study was approved by the institutional review boards for all hospitals. Of the 60 patients (30 treatment, 30 concurrent control subjects), all but 1 were enrolled at the University of Washington NICU.

Patient Selection
Patients were eligible for the study when they met the following criteria: (1) gestational age of ≤28;6;7> weeks and birth weight of ≤1000 g; (2) consent obtained at <24 hours of age; and (3) umbilical catheter in place. Patients were excluded from the trial when they had major life-threatening anomalies or hematopoietic crises such as disseminated intravascular coagulation, hemolysis as a result of blood group incompatibilities, or polycythemia. Concurrent control subjects met these enrollment criteria but were not approached by 24 hours of age, did not have central arterial access, or consent from legal guardians was given for data collection only.

Criteria for Withholding or Stopping the Study Drug
Criteria for withholding or stopping the study drug included neutropenia (absolute neutrophil count of <500/µL), a hematocrit level of >50% (not attributable to transfusion) with a reticulocyte count of ≥200000 cells per µL, or hypertension (defined as systolic blood pressure of >100 mmHg).

Administration of rEpo
A single lot of rEpo (Epogen, Epoetin Alfa Recombinant [Amgen, Thousand Oaks, CA]) was purchased through the University of Washington hospital pharmacy. Study drug was dispensed from the Investigational Drug Services pharmacist in single-dose 1-mL syringes that contained the preservative-free solutions of rEpo in concentrations of 4000 U/mL. rEpo was administered through a peripheral or central vein as a bolus injection, followed by a saline flush through the most proximal port possible. The flush volume was at least 3 times the volume of the tubing. Epo blood samples were drawn from a different site to avoid specimen contamination.

Data and Safety Monitoring Board
The data and safety monitoring board was chaired by a neonatologist who was not involved with the study and included a nephrologist and a neuroscientist. Data for each group of 10 infants were reviewed before progression to the next higher dosage. All unexpected serious adverse events were reviewed. As requested by the Food and Drug Administration, a 3-week interval was observed between dosing groups to allow possible hematopoietic adverse effects of rEpo (eg, polycythemia) to manifest.

Data Collected
Daily minimum and maximum mean blood pressure for first 2 weeks of life and weight were recorded, as were weekly complete blood counts, zinc protoporphyrin-to-heme ratios,20 and the number and volume of blood transfusions. Renal function (serum urea nitrogen and creatinine) and liver function (total and direct bilirubin and alkaline phosphatase) tests were obtained as clinically indicated. Data points were averaged by week for each patient. Data regarding complications of extreme prematurity (incidence and severity of ICH, periventricular leukomalacia (PVL), patent ductus arteriosus (PDA), bronchopulmonary dysplasia, necrotizing enterocolitis (NEC), infection, ROP, hearing deficits, and death were collected.

Urine isoprostane/urine creatinine,21 total antioxidant capacity (TAOC),22 and non–transferrin-bound iron23,24 were assessed at study entry and at 2 weeks of life for patients who were administered rEpo. During the study, the protocol was modified such that blood for these tests was drawn only from infants who weighed >700 g at birth and had arterial lines in place. These tests were not assessed for concurrent control subjects.

Data Analysis
Pharmacokinetic Analysis
Each of the 3 rEpo doses was administered at time 0, 24, and 48 hours. Blood samples (0.1 mL per sample) were collected from the umbilical artery catheter to measure plasma Epo concentrations at timed intervals: 0 (predose baseline); 5, 10, 15, and 30 minutes; and 1, 3, 6, 12, 24, 24.5, 48, 48.5, and 72 hours. First-dose concentrations were used to compute pharmacokinetic parameters after plasma Epo concentrations were corrected for endogenous, baseline values by subtracting the predose concentrations from subsequent values.25,26 Data analysis was conducted using noncompartmental pharmacokinetic techniques.27,28 The elimination rate constant (k) for the plasma data were derived using linear regression to compute the slope of the ln plasma Epo concentration versus time data during the terminal portion of the curve. The trapezoidal rule was used to compute the area under plasma concentration versus time curve (AUC) until the last measured value at 24 hours. The AUC was extended to infinity by taking the quotient of the 24-hour concentration and the elimination rate constant.

The half-life (t1/2) for the plasma Epo concentration versus time curve was computed by dividing 0.693 by the elimination rate constant. Clearance, volume of distribution (using the steady-state [Vss] and area [Varea] methods), and mean residence time (MRT) were calculated by using the following formulas: clearance = D/AUC; Vss = [D(AUMC)]/AUC2; Varea = D/[k(AUC)]; and MRT = AUMC/AUC, where D is the rEpo dosage and AUMC is the area under the first moment curve (computed by using the trapezoidal rule to the last measured concentration and extrapolated to infinity).27,28

The presence of nonlinear pharmacokinetics was identified by plotting the AUC versus dosage. Accumulation after multiple doses and the attainment of steady state was assessed by comparison of concentrations that were obtained 30 minutes (C0.5 hours, C24.5 hours, and C48.5 hours represent peak concentrations) and 24 hours (C24 hours, C48 hours, and C72 hours represent trough concentrations) after the 3 rEpo doses.

Epo Measurements
Plasma Epo concentrations were measured using the Quantikine IVD human Epo immunoassay enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, MN). Depending on the dosage administered and the collection time, blood samples were evaluated undiluted or at appropriate dilutions that ranged from 1:2 to 1:300.

Statistical Analysis
Statistical analysis of pharmacokinetic and safety data was conducted by using 1-way analysis of variance for between-subject and repeated-measures analysis of variance for within-subject comparisons, followed by posthoc testing when appropriate (SPSS software [SPSS Inc, Chicago, IL]). Posthoc tests include Tukey's honestly significant differences (HSD) and paired or unpaired t test. P < .05 was considered significant.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
During the study enrollment period, 82 infants who met weight and gestational age criteria were live born and 68 were admitted to the NICU. Of these infants, 37 were male, 23 were delivered vaginally, and 58 were singleton pregnancies. An additional 6 infants were transferred to the University of Washington NICU in their first hours of life. A total of 60 infants were studied: 30 received high-dose rEpo, and 30 served as concurrent control subjects. Concurrent control subjects were selected as consecutive eligible admissions until the required number was achieved. In the rEpo treatment group, 1 infant (2500 U/kg per dose) had a protocol violation, so blood samples from this infant were not included in the pharmacokinetic analysis. No infants were taken off protocol as a result of medication complications. At study entry, the control and treatment groups had comparable demographic data, as shown in Table 1.


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  		TABLE 1 Demographic Data

 
Pharmacokinetics
Figure 1 shows that the overall exposure to circulating Epo (AUC) increased in a nonlinear manner with increasing dosage. As the rEpo dosage increased, disproportionately larger increases in AUC were noted (P < .0001; Table 2). The mean AUC ratios were 2.6 for the 1000-U/kg and 500-U/kg dosages and 10.1 for the 2500-U/kg and 500-U/kg dosages. This nonlinear increase in AUC is attributable to a dosage-dependent decrease in clearance (53% decrease from 500 U/kg to 2500 U/kg; P < .0001) and a corresponding increase in the mean residence time (60% increase from 500 U/kg to 2500 U/kg; P < .02). We should note also that the changes in t1/2 were on the margin of significance (P = .056). Distribution volumes did not change as dosage increased.


Figure 1
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  		FIGURE 1 AUC for rEpo plasma concentration-time curve versus Epo dosage. The relationship between AUC and dosage for 500 U/kg (n = 10), 1000 U/kg (n = 10), and 2500 U/kg (n = 9) is nonlinear. The reason that Epo exhibits nonlinear pharmacokinetics is that clearance decreases with increasing dosage.

 

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  		TABLE 2 rEpo Pharmacokinetics According to Dosage (Mean ± SEM)

 
Figure 2 shows the mean change in plasma Epo concentration over time for each dosing group. Baseline Epo concentrations before dosing ranged from undetectable (<0.06 mU/mL) to 546 mU/mL, with a mean of 74.5 and a median value of 2 mU/mL. Mean Epo concentrations 30 minutes after rEpo infusion were 5973 ± 266, 12291 ± 403, and 34197 ± 1641 mU/mL after 500, 1000, or 2500 U/kg, respectively. At the 500 U/kg dosage, Epo peak and trough concentrations accumulated between the first and second doses (peak: P < .02; trough: P < .007) but leveled off after the third dose. At dosages of 1000 U/kg and 2500 U/kg, there was no significant accumulation of rEpo in plasma after the first dose. On the basis of this analysis, steady-state plasma Epo concentrations were attained by the second dose for all 3 dosages.


Figure 2
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  		FIGURE 2 Plasma concentration of rEpo after intravenous injection. Peak (P < .02) and trough (P < .007) rEpo concentrations rose significantly between the first and second doses of 500 U/kg but showed no additional increase after the third dose. For the 1000 U/kg and 2500 U/kg dosages, there was no significant accumulation of rEpo after the first dose.

 
Clinical Outcomes
There were no unexpected serious adverse events in patients who received high-dose rEpo at any of the studied doses. During the treatment period, mean arterial blood pressure was no different between groups, with mean daily values in control infants increasing from 32.0 ± 5.0 mmHg on the first day of life to 37.1 ± 5.5 mmHg by 3 days, compared with 31.3 ± 4.4 to 35.6 ± 4.6 mmHg in rEpo-treated infants (Fig 3); however, control infants tended to require more support to remain normotensive, with more frequent use of fluid boluses and pressors (Fig 3). Table 3 shows that the overall incidence of ICH and PVL was not different between groups, although fewer rEpo-treated infants had ICH (P = .07), and fewer infants had grade IV ICH or PVL (P = .06). The overall incidence of ROP was not different between groups; neither was there a difference in ROP severity or in the need for laser eye surgery. Although there was no difference between the groups in the overall incidence of NEC, none of the rEpo-treated infants who had a diagnosis of NEC required surgery (P = .018). The majority of infants in both groups had documented PDA, with no difference between groups. The incidence of acute and chronic respiratory problems (respiratory distress syndrome, pulmonary interstitial emphysema, and bronchopulmonary dysplasia) was not different between treatment groups. For the infants whose for hearing was tested (42 of 60 infants), there were no differences between groups.


Figure 3
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  		FIGURE 3 A, Blood pressure and pressor treatment received. Shown is the mean (±SEM) blood pressure measured from birth through day 3 of life. B, The number of fluid boluses (squares), pressor treatments (circles), and hydrocortisone days (diamonds) used to treat hypotension for each group. rEpo was given on days 1 to 3. NS indicates normal saline; HC, hydrocortisone.

 

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  		TABLE 3 Complications of Prematurity

 
Three infants in the rEpo group had skin hemangiomas documented before discharge. Two of the affected infants received 500 U/kg, and 1 infant received 2500 U/kg. Two of the 3 also received 14 to 21 days of rEpo to treat anemia, beginning at 6 weeks of age.

Serious infections were common in both groups during the hospital stay. In the rEpo arm, 10 infants had 12 proven bloodstream infections (7 Staphylococcus species, 1 group B Streptococcus, 2 Pseudomonas, 1 Klebsiella, and 1 HSV2), 3 infants had meningitis (1 HSV2, 1 S aureus, and 1 presumptive viral infection), and 1 infant had a documented urinary tract infection. These infections were distributed across all rEpo treatment groups. Similarly, 11 control infants had 12 bloodstream infections (9 Staphylococcus species, 1 Klebsiella, 1 Escherichia coli, and 1 group B Streptococcus), 1 infant had Staphylococcus sepsis with meningitis, and 5 infants had urinary tract infections (2 Klebsiella and 1 E coli).

Survival between groups was not different. Four control infants died during the neonatal period: 3 had grade 4 ICH in addition to severe respiratory distress, 1 had a pulmonary hemorrhage, and 1 had an intestinal perforation with internal bleeding. Death occurred on days 2 and 3. In the rEpo arm, there was 1 neonatal death per treatment group: 1 died of Pseudomonas sepsis on day 8, 1 of respiratory failure with pulmonary interstitial emphysema on day 8, and 1 from sequelae of gastric and intestinal perforation in addition to a grade 4 ICH on day 18. In addition, there were 2 late deaths: 1 was attributed to a surgical complication of PDA ligation on day 29, and the other was attributed to complications of osteomyelitis, liver failure, pulmonary hypertension, and cardiac failure at day 82 of life.

For infants who survived the neonatal period, the length of hospital stay ranged from 27 to 231 days for control infants and 24 to 159 days for rEpo-treated infants. The mean ± SD and median stay for control subjects were 91.1 ± 40.4 and 86.5 days (n = 26) compared with 83.9 ± 36.1 and 83 days (n = 27) for rEpo-treated infants.

Laboratory Parameters
High-dose rEpo given in the first 3 days of life had no clinically significant effect on any laboratory parameter. Infants who received 2500 U/kg had a significant increase in reticulocytes and nucleated red blood cells noted in week 2 of life, but there was no difference in hematocrit or number of blood transfusions. As might be expected with a brief increase in erythropoiesis, zinc protoporphyrin-to-heme ratios increased in the second week of life, suggesting increased iron use (Fig 4). During the initial hospitalization, rEpo-treated infants received 5.2 ± 3.4 transfusions (range: 1–22), compared with control subjects (4.6 ± 4.0; range: 0–14). Two infants in the rEpo group received an unusually large number of transfusions (15 and 22); 1 had disseminated intravascular coagulopathy associated with late sepsis, and the other had a torn PDA during surgery that resulted in death. The mean volume of blood transfused into the rEpo survivors was 75 ± 40 (median: 73 mL) compared with 79 ± 80 (median: 67 mL) in control subjects. When all infants are included, the mean volume of blood transfused into the rEpo-treated infants was 90 ± 97 (median: 73 mL) compared with 72 ± 76 (median: 56 mL) in control subjects. The use of rEpo to stimulate erythropoiesis later during hospitalization was not different between groups: 15 rEpo-treated infants received late rEpo, compared with 14 control subjects.


Figure 4
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  		FIGURE 4 Effect of high-dose rEpo on erythropoiesis and iron use. Shown is the mean (±SEM) hematocrit level for each treatment group according to week of life (A) with corresponding absolute reticulocyte count (B) and zinc protoporphyrin (ZnPP)/heme ratio (C).

 
No abnormalities of any blood cell line resulted from rEpo treatment. Specifically, no neutropenia, neutrophilia, thrombocytopenia, thrombophilia, or polycythemia occurred in rEpo-treated infants. There was also no difference in renal function tests (serum urea nitrogen or creatinine) or liver function tests (bilirubin and alkaline phosphatase) between groups.

Baseline and 2-week measures of TAOC, non–transferrin-bound iron, and urine isoprostane/urine creatinine ratios are shown in Table 4. There were no differences between these measures when baseline and 2-week values are compared within treatment groups (ie, high-dose rEpo was not associated with a significant increase or decrease in these values). There were differences unrelated to rEpo treatment in the TAOC and free iron values between groups such that the 1000 U/kg per dose group had higher TAOC values at study entry and the 2500 U/kg per dose group had higher free iron values at both entry and 2 weeks of age.


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  		TABLE 4 Antioxidant, Isoprostane, and Iron Values

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
This phase I/II study examined the pharmacokinetics of 3 doses of intravenous rEpo in newborn ELBW infants, with the secondary goal of assessing rEpo safety in this population.

Pharmacokinetics
As expected from pharmacokinetic studies of erythropoietic dosages of rEpo in ELBW infants,25,29 high-dose rEpo followed nonlinear pharmacokinetics (Fig 1). When dosages were increased two- and fivefold (1000 U/kg and 2500 U/kg) compared with the 500 U/kg doses, AUC increased 2.6 and 10.1 times, respectively. Although there is still some uncertainty about Epo clearance,30–32 it seems that rEpo is not substantially metabolized by the liver or eliminated unchanged by the kidney.32–37 Recent data suggest that rEpo is primarily degraded by erythroid progenitors located in bone marrow26; therefore, it is reasonable to speculate that nonlinear rEpo pharmacokinetics are attributable to the limited number of Epo receptors (Epo-R) available on red blood cell precursors.38–40 As the dosage of rEpo increases, binding to Epo-R becomes relatively saturated, breakdown of rEpo slows, and rEpo clearance decreases. Also, as Epo-R binding sites are increasingly occupied with rising dosages, it is possible that rEpo volume of distribution could decrease at higher dosages.

We saw no substantial change in t1/2 between rEpo dosing groups. Given that t1/2 is directly related to clearance and volume of distribution (V) by the formula t1/2 = [0.693V]/clearance, the stable t1/2 indicates that changes in clearance and volume of distribution offset one another. Comparing the data between the lowest and highest dosing groups, clearance decreased from 17.3 ± 1.8 mL/hour per kg to 8.2 ± 0.6 mL/hour per kg (P < .0001), whereas volume of distribution at steady state changed from 109 ± 8 mL/kg to 89 ± 14 mL/kg (nonsignificant).

Correspondingly, mean residence time increased from 6.7 ± 0.6 hours to 10.7 ± 1.3 hours (P < .02), and t1/2 increased from 5.4 ± 0.6 hours to 8.7 ± 1.4 hours (nonsignificant) from the lowest to the highest dosage. All of these changes are consistent with a saturable site in the bone marrow that mediates degradation of rEpo in humans. By this mechanism, the previous observations that volume of distribution and clearance are higher in ELBW infants compared with adults would be expected because infants have a higher proportion of red marrow space than older humans.26

For agents that follow nonlinear pharmacokinetics, it is important to assess accumulation of drug after multiple doses and the time needed to attain steady-state conditions. Nonlinear pharmacokinetics can lead to excessive accumulation and prolonged time to steady state. For doses up to 2500 U/kg per day administered for 3 consecutive days, peak and trough concentrations were stable after the second dose, and steady-state conditions were achieved within 24 to 48 hours.

Preliminary Safety
To the degree possible in a phase I/II study, the safety of administration of high-dose rEpo to ELBW infants in the first 3 days of life was assessed, with particular attention given to adverse effects that have been noted in adults (hypertension, increased thrombosis, seizures, strokes, polycythemia, immune-mediated anemia, or death),13 and those anticipated on the basis of the distribution of Epo receptors and their potential actions during development.41 It is important that we acknowledge that a large, randomized, control trial will be required to establish safety definitively. Nevertheless, we found no evidence of unexpected serious adverse events attributable to rEpo. Specifically, there was no hypertension and no increase in thrombotic events, seizures, strokes, polycythemia, immune-mediated anemia, or death in any of the rEpo treatment groups. There was also no increase in the incidence or severity of ROP, a concern that has previously been raised.19 There were also no differences in free iron or indicators of oxidative injury between groups.

Assessment of long-term neurodevelopmental outcomes was beyond the scope of this study. Nonetheless, it was encouraging to note that even in this phase I/II trial, there were trends toward benefit in many aspects of the health of infants who received high-dose rEpo. The severity of ICH and white matter injury was diminished (P = .06). Although there is a great deal of evidence from animal models of brain injury that once an injury occurs rEpo is protective, it was unexpected that the incidence or severity of intracranial bleeding might be affected. Improved cardiovascular stability might decrease fluctuations in cerebral perfusion, decreasing risk for hemorrhage during the critical first days of life.7 rEpo-treated infants received fewer fluid boluses and less vasopressor support in the first 2 days of life. Furthermore, rEpo has been shown to lessen vasoconstriction after subarachnoid hemorrhage and to lessen subsequent neurologic injury.42 We can speculate that rEpo might have similar stabilizing effects in this patient population. Early rEpo was also associated with decreased severity of NEC. Epo receptors are present in the developing intestine, and rEpo has previously demonstrated trophic and protective effects in this system.43,44


   CONCLUSIONS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
The pharmacokinetics of intravenous rEpo differs from intraperitoneal or subcutaneous dosing and results in a more rapid, higher peak concentration, with more rapid clearance. We know that in rat pups subjected to hypoxia-ischemia, neuroprotection is achieved with 5000 U/kg rEpo given intraperitoneally or subcutaneously. Such dosing results in peak plasma concentrations between 6000 and 12000 mU/kg, with sustained levels in the 6000 mU/mL range for up to 12 hours.12 In this study, both 1000 U/kg and 2500 U/kg rEpo intravenously resulted in peak concentrations that, on the basis of animal studies, are likely to be therapeutic9,12; however, only the 2500 U/kg dosage provided plasma levels >6000 mU/mL 12 hours after injection. This study provides essential data needed to inform future clinical trials. More studies are needed to determine whether it is peak concentration or overall exposure that is most important for optimal neuroprotection.


   ACKNOWLEDGMENTS
 
This study was supported by a grant from the Children's Hospital and Regional Medical Center.

We thank Joan Zerzan, Jared Boasen, Sheree Miller, the University of Washington Neonatal Nursing Staff and Faculty, and the participating families for invaluable assistance with this project. We also thank Paola Costa-Mallen, S.M. Hossein Sadrzadeh, and Mike Edenfield for help in assessing the indicators of oxidative injury.


   FOOTNOTES
 
Accepted Dec 4, 2007.

Address correspondence to Sandra E. Juul, MD, PhD, University of Washington, Department of Pediatrics, Division of Neonatology, Box 356320, Seattle, WA 98195. E-mail: sjuul{at}u.washington.edu

The authors have indicated they have no financial relationships relevant to this article to disclose.


What's Known on This Subject

There have been no published studies of high-dose rEpo pharmacokinetics or safety in ELBW infants or any other pediatric population. Dosages used for neuroprotection are ~10-fold higher than erythropoietic dosages, so this information is needed before proceeding to a randomized, controlled trial of neuroprotection.

 

What This Study Adds

This study provides essential data needed to proceed with neuroprotective studies of ELBW infants. We show the pharmacokinetics of 3 dosages of rEpo that were given to ELBW infants in the first 3 days of life. We also provide safety information.

 


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 

  1. Meadow W, Lee G, Lin K, Lantos J. Changes in mortality for extremely low birth weight infants in the 1990s: implications for treatment decisions and resource use. Pediatrics. 2004;113 (5):1223 –1229[Abstract/Free Full Text]
  2. Hack M, Youngstrom EA, Cartar L, et al. Behavioral outcomes and evidence of psychopathology among very low birth weight infants at age 20 years. Pediatrics. 2004;114 (4):932 –940[Abstract/Free Full Text]
  3. Litt J, Taylor HG, Klein N, Hack M. Learning disabilities in children with very low birthweight: prevalence, neuropsychological correlates, and educational interventions. J Learn Disabil. 2005;38 (2):130 –141[Abstract/Free Full Text]
  4. Wilson-Costello D, Friedman H, Minich N, Fanaroff AA, Hack M. Improved survival rates with increased neurodevelopmental disability for extremely low birth weight infants in the 1990s. Pediatrics. 2005;115 (4):997 –1003[Abstract/Free Full Text]
  5. Moore M, Gerry Taylor H, Klein N, Minich N, Hack M. Longitudinal changes in family outcomes of very low birth weight. J Pediatr Psychol. 2006;31 (10):1024 –1035[Abstract/Free Full Text]
  6. Vohr BR, Wright LL, Dusick AM, et al. Center differences and outcomes of extremely low birth weight infants. Pediatrics. 2004;113 (4):781 –789[Abstract/Free Full Text]
  7. Kluckow M, Evans N. Low superior vena cava flow and intraventricular haemorrhage in preterm infants. Arch Dis Child Fetal Neonatal Ed. 2000;82 (3):F188 –F194[Abstract/Free Full Text]
  8. Demers EJ, McPherson RJ, Juul SE. Erythropoietin protects dopaminergic neurons and improves neurobehavioral outcomes in juvenile rats after neonatal hypoxia-ischemia. Pediatr Res. 2005;58 (2):297 –301[CrossRef][Web of Science][Medline]
  9. Kellert BA, McPherson RJ, Juul SE. A comparison of high-dose recombinant erythropoietin treatment regimens in brain-injured neonatal rats. Pediatr Res. 2007;61 (4):451 –455[CrossRef][Web of Science][Medline]
  10. Dzietko M, Felderhoff-Mueser U, Sifringer M, et al. Erythropoietin protects the developing brain against N-methyl-D-aspartate receptor antagonist neurotoxicity. Neurobiol Dis. 2004;15 (2):177 –187[CrossRef][Web of Science][Medline]
  11. Keller M, Yang J, Griesmaier E, et al. Erythropoietin is neuroprotective against NMDA-receptor-mediated excitotoxic brain injury in newborn mice. Neurobiol Dis. 2006;24 (2):357 –366[CrossRef][Web of Science][Medline]
  12. Statler PA, McPherson RJ, Bauer LA, Kellert BA, Juul SE. Pharmacokinetics of high-dose recombinant erythropoietin in plasma and brain of neonatal rats. Pediatr Res. 2007;61 (6):671 –675[Web of Science][Medline]
  13. Amgen. Epogen (epoietin alfa) for injection. 2005. Available at: www.fda.gov/medwatch/safety/2008/epo_DHCP_03102008.pdf. Accessed June 17, 2008
  14. Ohls RK. The use of erythropoietin in neonates. Clin Perinatol. 2000;27 (3):681 –696[CrossRef][Web of Science][Medline]
  15. Juul SE, McPherson RJ, Farrell FX, Jolliffe L, Ness DJ, Gleason CA. Erythropoietin concentrations in cerebrospinal fluid of nonhuman primates and fetal sheep following high-dose recombinant erythropoietin. Biol Neonate. 2004;85 (2):138 –144[CrossRef][Web of Science][Medline]
  16. Ehrenreich H, Hasselblatt M, Dembowski C, et al. Erythropoietin therapy for acute stroke is both safe and beneficial. Mol Med. 2002;8 (8):495 –505[Web of Science][Medline]
  17. Ehrenreich H, Hinze-Selch D, Stawicki S, et al. Improvement of cognitive functions in chronic schizophrenic patients by recombinant human erythropoietin. Mol Psychiatry. 2007;12 (2):206 –220[CrossRef][Web of Science][Medline]
  18. Pollak A, Hayde M, Hayn M, et al. Effect of intravenous iron supplementation on erythropoiesis in erythropoietin-treated premature infants. Pediatrics. 2001;107 (1):78 –85[Abstract/Free Full Text]
  19. Ohlsson A, Aher SM. Early erythropoietin for preventing red blood cell transfusion in preterm and/or low birth weight infants. Cochrane Database Syst Rev. 2006;(3):CD004863
  20. Juul SE, Zerzan JC, Strandjord TP, Woodrum DE. Zinc protoporphyrin/heme as an indicator of iron status in NICU patients. J Pediatr. 2003;142 (3):273 –278[CrossRef][Web of Science][Medline]
  21. Roberts IIL, Morrow J. Measurement of F2-isoprostanes as an index of oxidative stress in vivo. Free Radic Biol Med. 2000;28 (4):505 –513[CrossRef][Web of Science][Medline]
  22. Miller NJ, Rice-Evans C, Davies MJ, Gopinathan V, Milner A. A novel method for measuring antioxidant capacity and its application to monitoring the antioxidant status in premature neonates. Clin Sci (Lond). 1993;84 (4):407 –412[Medline]
  23. Buonocore G, Perrone S, Longini M, et al. Non protein bound iron as early predictive marker of neonatal brain damage. Brain. 2003;126 (Pt 5):1224 –1230[Abstract/Free Full Text]
  24. Gosriwatana I, Loreal O, Lu S, Brissot P, Porter J, Hider R. Quantification of non-transferrin-bound iron in the presence of unsaturated transferrin. Anal Biochem. 1999;273 (2):212 –220[CrossRef][Web of Science][Medline]
  25. Widness JA, Veng-Pedersen P, Peters C, Pereira LM, Schmidt RL, Lowe LS. Erythropoietin pharmacokinetics in premature infants: developmental, nonlinearity, and treatment effects. J Appl Physiol. 1996;80 (1):140 –148[Abstract/Free Full Text]
  26. Widness JA, Schmidt RL, Hohl RJ, et al. Change in erythropoietin pharmacokinetics following hematopoietic transplantation. Clin Pharmacol Ther. 2007;81 (6):873 –879[CrossRef][Web of Science][Medline]
  27. Benet LZ, Galeazzi RL. Noncompartmental determination of the steady-state volume of distribution. J Pharm Sci. 1979;68 (8):1071 –1074[Web of Science][Medline]
  28. Perrier D, Mayersohn M. Noncompartmental determination of the steady-state volume of distribution for any mode of administration. J Pharm Sci. 1982;71 (3):372 –373[CrossRef][Web of Science][Medline]
  29. Brown MS, Jones MA, Ohls RK, Christensen RD. Single-dose pharmacokinetics of recombinant human erythropoietin in preterm infants after intravenous and subcutaneous administration. J Pediatr. 1993;122 (4):655 –657[Web of Science][Medline]
  30. Bozzini CE. Influence of the erythroid activity of the bone marrow on the plasma disappearance of injected erythropoietin in dogs. Nature. 1966;209 (5028):1140 –1141
  31. Erslev AJ, Wilson J, Caro J. Erythropoietin titers in anemic, nonuremic patients. J Lab Clin Med. 1987;109 (4):429 –433[Web of Science][Medline]
  32. Emmanouel DS, Goldwasser E, Katz AI. Metabolism of pure human erythropoietin in the rat. Am J Physiol. 1984;247 (1 pt 2):F168 –F176[Web of Science][Medline]
  33. Macdougall IC, Roberts DE, Coles GA, Williams JD. Clinical pharmacokinetics of epoetin (recombinant human erythropoietin). Clin Pharmacokinet. 1991;20 (2):99 –113[Web of Science][Medline]
  34. Schuster SJ, Caro J. Erythropoietin: physiologic basis for clinical applications. Vox Sang. 1993;65 (3):169 –179[Web of Science][Medline]
  35. Kindler J, Eckardt KU, Ehmer B, Jandeleit K, Kurtz A, Schreiber A, Scigalla P, Sieberth HG. Single-dose pharmacokinetics of recombinant human erythropoietin in patients with various degrees of renal failure. Nephrol Dial Transplant. 1989;4 (5):345 –349[Abstract/Free Full Text]
  36. Widness JA, Veng-Pedersen P, Schmidt RL, Lowe LS, Kisthard JA, Peters C. In vivo 125I-erythropoietin pharmacokinetics are unchanged after anesthesia, nephrectomy and hepatectomy in sheep. J Pharmacol Exp Ther. 1996;279 (3):1205 –1210[Abstract/Free Full Text]
  37. Spivak JL, Hogans BB. The in vivo metabolism of recombinant human erythropoietin in the rat. Blood. 1989;73 (1):90 –99[Abstract/Free Full Text]
  38. Kato M, Kato Y, Sugiyama Y. Mechanism of the upregulation of erythropoietin-induced uptake clearance by the spleen. Am J Physiol. 1999;276 (5 pt 1):E887 –E895[Web of Science][Medline]
  39. Sawyer ST, Krantz SB, Goldwasser E. Binding and receptor-mediated endocytosis of erythropoietin in Friend virus-infected erythroid cells. J Biol Chem. 1987;262 (12):5554 –5562[Abstract/Free Full Text]
  40. Mufson RA, Gesner TG. Binding and internalization of recombinant human erythropoietin in murine erythroid precursor cells. Blood. 1987;69 (5):1485 –1490[Abstract/Free Full Text]
  41. Juul SE, Yachnis AT, Christensen RD. Tissue distribution of erythropoietin and erythropoietin receptor in the developing human fetus. Early Hum Dev. 1998;52 (3):235 –249[CrossRef][Web of Science][Medline]
  42. Grasso G, Buemi M, Alafaci C, et al. Beneficial effects of systemic administration of recombinant human erythropoietin in rabbits subjected to subarachnoid hemorrhage. Proc Natl Acad Sci USA. 2002;99 (8):5627 –5631[Abstract/Free Full Text]
  43. Juul SE, Joyce AE, Zhao Y, Ledbetter DJ. Why is erythropoietin present in human milk? Studies of erythropoietin receptors on enterocytes of human and rat neonates. Pediatr Res. 1999;46 (3):263 –268[Web of Science][Medline]
  44. Juul SE, Ledbetter DJ, Joyce AE, et al. Erythropoietin acts as a trophic factor in neonatal rat intestine. Gut. 2001;49 (2):182 –189[Abstract/Free Full Text]
PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics

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