Completion of radical hysterectomy does not improve survival of patients with cervical cancer and intraoperatively detected lymph node involvement: ABRAX international retrospective cohort study.

BACKGROUND: The management of cervical cancer patients with intraoperative detection of lymph node involvement remains controversial. Since all these patients are referred for (chemo)radiation after the surgery, the key decision is whether radical hysterectomy should be completed as originally planned, taking into account an additional morbidity associated with extensive surgical dissection prior to adjuvant treatment. The ABRAX study investigated whether completing a radical uterine procedure is associated with an improved oncological outcome of such patients. PATIENTS AND METHODS: We performed retrospective analyses of 515 cervical cancer patients (51 institutions, 19 countries) who were referred for primary curative surgery between 2005 and 2015 (stage IA-IIB, common tumour types) in whom lymph node involvement was detected intraoperatively. Patients were stratified according to whether the planned uterine surgery was completed (COMPL group, N = 361) or abandoned (ABAND group, N = 154) to compare progression-free survival. Definitive chemoradiation was given to 92.9% patients in the ABAND group and adjuvant (chemo)radiation or chemotherapy to 91.4% of patients in the COMPL group. RESULTS: The risks of recurrence (hazard ratio [HR] 1.154, 95% confidence intervals [CI] 0.799-1.666, P = 0.45), pelvic recurrence (HR 0.836, 95% CI 0.458-1.523, P = 0.56), or death (HR 1.064, 95% CI 0.690-1.641, P = 0.78) were not significantly different between the two groups. No subgroup showed a survival benefit from completing radical hysterectomy. Disease-free survival reached 74% (381/515), with a median follow-up of 58 months. Prognostic factors were balanced between the two groups. FIGO stage and number of pelvic lymph nodes involved were significant prognostic factors in the whole study cohort. CONCLUSION: We showed that the completion of radical hysterectomy does not improve survival in patients with intraoperatively detected lymph node involvement, regardless of tumour size or histological type. If lymph node involvement is confirmed intraoperatively, abandoning uterine radical procedure should be considered, and the patient should be referred for definitive chemoradiation. CLINICAL TRIALS IDENTIFIER: NCT04037124.

A novel PCR-based point-of-care method facilitates rapid, efficient, and sensitive diagnosis of influenza virus infection.

OBJECTIVE: The aim of this single-centre study was the comparative analysis of the GeneXpert (Cepheid Inc.) and the LIAT (Roche) system for the rapid polymerase chain reaction (PCR)-based detection of influenza A (IA) and influenza B (IB) viruses. PATIENTS AND METHODS: During the 2017-2018 flu season, 651 prospectively collected samples (throat and nasal swabs) of patients with symptoms of influenza-like illness or acute respiratory infection were tested for the presence of IA and IB viruses using the GeneXpert and LIAT systems. To evaluate the usefulness for near-patient testing, a LIAT system was installed at the Department of Emergency Medicine, and sample testing was performed on site. Reference testing of all samples was performed with the Xpert Flu assay and for 313 samples in addition with the Xpert Xpress Flu/RSV (respiratory syncytial virus) assay at the central laboratory. Analysis of all samples was carried out within 24 hr after collection. RESULTS: Overall, 267 of the 651 samples analysed were positive for influenza viruses in at least one of the three assays investigated (IA, 88; IB, 179). The overall rates of agreement between the LIAT assay and the Xpert Flu assay was 96.0% for the detection of IA and IB viruses. The sensitivity and specificity of the LIAT assay compared to the Xpert Flu assay for the detection of IA was 98.80% (95% confidence interval (CI) 93.47-99.97%) and 99.12% (95% CI, 97.96% to 99.71%) and for the detection of IB 98.76% (95% CI 95.58-99.85%), and 96.33% (95% CI 94.26-97.81%), respectively. The LIAT assay showed a statistically significant higher detection rate of IB virus than the Xpert Flu assay (p <0.01). No significant difference was found between the detection rate of the LIAT assay and the Xpert Xpress Flu/RSV assay. The mean time to the availability of a definite test result was significantly shorter with the on-site LIAT system than the GeneXpert system (mean 59 min saving time; p <0.01). CONCLUSION: The LIAT system represents a robust and highly sensitive point-of-care device for the rapid PCR-based detection of influenza A and influenza B viruses.

Combining clinicopathological predictors and molecular biomarkers in the oncogenic K-RAS/Ki67/HIF-1α pathway to predict survival in resectable pancreatic cancer.

BACKGROUND: The dismal prognosis of patients diagnosed with pancreatic cancer points to our limited arsenal of effective anticancer therapies. Oncogenic K-RAS hyperactivation is virtually universal in pancreatic cancer, that confers drug resistance, drives aggressive tumorigenesis and rapid metastasis. Pancreatic tumours are often marked by hypovascularity, increased hypoxia and ineffective drug delivery. Thus, biomarker discovery and developing innovative means of countervailing oncogenic K-RAS activation are urgently needed. METHODS: Tumour specimens from 147 pancreatic cancer patients were analysed by immunohistochemical (IHC) staining and tissue microarray (TMA). Statistical correlations between selected biomarkers and clinicopathological predictors were examined to predict survival. RESULTS: We find that heightened hypoxia response predicts poor clinical outcome in resectable pancreatic cancer. SIAH is a tumour-specific biomarker. The combination of five biomarkers (EGFR, phospho-ERK, SIAH, Ki67 and HIF-1α) and four clinicopathological predictors (tumour size, pathological grade, margin and lymph node status) predict patient survival post surgery in pancreatic cancer. CONCLUSIONS: Combining five biomarkers in the K-RAS/Ki67/HIF-1α pathways with four clinicopathological predictors may assist to better predict survival in resectable pancreatic cancer.

Mathematical modelling can predict adequacy rates and needle passes for fine needle aspiration cytology with rapid on-site evaluation.

OBJECTIVE: Fine needle aspiration is widely used to obtain tissue samples. There are two types of sampling processes: fixed and variable. In fixed sampling, the samples are not observed for adequacy during the sampling process. In variable sampling, samples are evaluated for adequacy as they are received, and sampling is stopped as soon as an adequate sample is obtained. Each sample involves a risk of harm to the patient, and so limits are often imposed on the number of samples. The impact of such limits has not been investigated. The objective of this study was to determine the impact of sampling limits on the adequacy rate. METHODS: A mathematical model of the sampling process was developed. The model describes the per-case adequacy rate in terms of the per-pass probability of success, the number of needle passes, the accuracy of the assessor and an upper limit on the number of needle passes. RESULTS: Per-case adequacy was positively correlated with the per-pass adequacy and the accuracy of the assessor. Sampling limits reduced the per-case adequacy rate. The impact of sampling limits decreased as the sampling limit increased. The model provides good approximations of the adequacy rate even when the constant yield assumption is violated. CONCLUSION: Mathematical modelling provides a useful approach to study sampling processes that would be difficult to evaluate with clinical studies.

The effect of anticoagulant, storage temperature and dilution on cord blood hematology parameters over time.

The objective of the study was to determine whether selected hematologic parameters measured on umbilical cord blood samples using an automated hematology analyzer (Sysmex XE-2100) were affected by (i) anticoagulant (the specimens were collected in EDTA vs. sodium heparin), (ii) temperature (the specimens were maintained at 4 degrees C vs. room temperature for up to 72 h) and (iii) 1 : 5 dilution vs. undiluted using the manufacturer's diluting solution. Use of heparin, instead of EDTA, had little effect on the hematologic results (n = 8) except for lower platelet and progenitor cell counts. Results were remarkably stable for 72 h at either room temperature or 4 degrees C except for modest red blood cell swelling at 24 h. Specimens of blood diluted at 1 : 5 had an immediate small, but significant change on white cell count (+13.3%), reticulocyte count (-11.2%) and reticulocyte hemoglobin content (-19.6%). Diluted samples did not change further over 4 h at room temperature. With a 1 : 5 dilution, analysis of 40 microl of cord blood stored for 3 days at room temperature may provide useful hematologic information with little phlebotomy loss.

Change in erythropoietin pharmacokinetics following hematopoietic transplantation.

Pre-clinical studies have demonstrated that bone marrow ablation has a profound effect in decreasing erythropoietin (EPO) elimination. The study's objective was to determine in humans if EPO pharmacokinetics (PKs) are perturbed following bone marrow ablation. EPO PK studies were performed in eight subjects, aged 4 to 61 years, undergoing fully myeloablative hematopoietic stem cell transplantation. Serial PK studies using intravenous injection of recombinant human EPO (92+/-2.0 U/kg) (mean+/-SEM) were carried out during four periods of altered marrow integrity: baseline pre-ablation, post-ablation pre-transplant, early post-transplant pre-engraftment, and late post-transplant full engraftment. Compared with baseline, post-ablation pre-transplant and early post-transplant EPO PKs demonstrated declines in clearance increases in terminal elimination half-life of 36 and 95%, respectively. Clearance and half-life returned to baseline following full engraftment. The association of EPO elimination with decreased bone marrow activity in patients undergoing transplantation conclusively establishes the bone marrow as a key determinant of EPO elimination in humans.

A 'bottom-up' approach for endo-PK/PD analysis.

A 'bottom-up' PK/PD analysis approach employing system analysis principles of convolution/deconvolution and special nonparametric estimation procedures is presented to resolve the complex 'endo-PK/PD' of the endogenous form of recombinant drugs using erythropoietin (EPO) as an example. A novel cellular deconvolution algorithm is presented that facilitates the identification of the functional relationship between the variables involved in EPO's complex PK/PD. Five sheep each underwent two phlebotomies spaced 4-6 weeks apart when their hemoglobin levels were reduced from 12 g/dl to 3-4 g/dl. EPO levels and reticulocyte counts were frequently sampled. The data were analysed using end-constrained cubic splines. The rate of reticulocyte production was determined using the novel deconvolution methodology. The erythroid progenitor cells activation rate by EPO was estimated from the reticulocyte production rate using a lag-time parameter which determines the delay in the reticulocyte appearance in the blood relative to the activation of erythroid progenitors. Hysteresis minimization combined with cellular deconvolution was employed to determine the population PK/PD transduction function relating the progenitor activation rate to EPO concentrations in a nonparametric manner without assuming a specific structure. The proposed approach provides a rational informative starting point for developing parametric PK/PD models to resolve the complex endo-PK/PD of recombinant drugs.

Erythropoietin production rate in phlebotomy-induced acute anemia.

OBJECTIVE: To estimate the rate of erythropoietin (EPO) production under physiological, conditions and to examine the regulatory mechanism of EPO production in response to acute phlebotomy-induced anemia. METHODS: Six sheep each underwent two phlebotomies in which the hemoglobin (Hb) was reduced to 3-4 g/dl over 4-5 h. The EPO plasma level, reticulocytes, Hb and EPO clearance were followed by frequent blood sampling. The EPO production rate was determined by a semi-parametric method based on a disposition decomposition analysis that accounts for the nonlinear disposition kinetics of EPO and corrects for time-dependent changes in the clearance. RESULTS: The controlled drop in hemoglobin resulted in an abrupt increase in the plasma EPO concentration (peak level 812+/-40 mU/ml, mean+/-CV%) that was followed by a rapid drop 2-4 days after the phlebotomy at a time when the sheep were still anemic (Hb=4.3+/-16 g/dl). The EPO production rate at baseline was 43+/-52 U/day/kg and the amounts of EPO produced over an 8 day period resulting from the first and second phlebotomy were 2927+/-40 U/kg and 3012+/-31 U/kg, respectively. CONCLUSIONS: The rapid reduction in the EPO plasma level observed 2-4 days following the phlebotomy cannot be explained solely by the increase in EPO clearance but also by a reduction in EPO production.

Pharmacokinetic tracer kinetics analysis of changes in erythropoietin receptor population in phlebotomy-induced anemia and bone marrow ablation.

OBJECTIVES: The objective was to study in vivo erythropoietin (Epo) progenitor cell surface receptors (EpoR) in the bone marrow (BM) after phlebotomy and bone marrow ablation. METHODS: Serial tracer interaction method experiments were conducted in adult sheep at baseline and after phlebotomy (PH) and ablation (AB). PH was done 10 days after phlebotomy (to 3-4 g/dl Hb), and the AB was done 8 days after a 3-day oral treatment with bulsulfan (11 mg/kg/day). RESULTS: Bone marrow ablation changed the elimination from non-linear to linear, consistent with an abolition of the non-linear elimination via BM EpoRs. The phlebotomy increased the linear clearance of the ablated elimination pathway (from 63.6+/-12 to 126+/-64 ml/h/kg), consistent with an up-regulation of the erythroid progenitor BM-based EpoR pool, but did not change the clearance of the non-ablated elimination pathway (p>0.05). The EpoR pool size remaining after BM ablation was 7.4+/-2.7% of the pre-ablation pool. CONCLUSIONS: Erythropoietin elimination via EpoR in the bone marrow was non-linear and increased following phlebotomy-induced anemia. This is consistent with an up-regulation of the erythropoietic EpoR pool in BM. Assuming that the elimination of Epo after BM ablation was via non-hematopoietic EpoR, then this post-ablation EpoR population was not significantly up-regulated by the phlebotomy.

Pharmacokinetic/pharmacodynamic analysis of paradoxal regulation of erythropoietin production in acute anemia.

The regulatory mechanism responsible for a paradoxal, rapid drop in the erythropoietin (EPO) plasma level seen 2 to 4 days after acute, phlebotomy-induced anemia was investigated in seven adult sheep. To introduce acute anemia, each sheep underwent two phlebotomies where the hemoglobin (Hb) was reduced to 3 or 4 g/dl over 4 to 5 h. The phlebotomies were spaced 4 to 6 weeks apart in three animals, and 8 days apart in four other animals. EPO plasma levels, reticulocyte count, Hb, and p50 for oxygen-Hb dissociation were determined from frequent blood samplings throughout the study period. EPO's disposition pharmacokinetic (PK) and plasma clearance were determined from i.v. bolus injections of tracer amounts of a recombinant human EPO tracer. The controlled drop in Hb resulted in a rapid increase in plasma EPO to 836 +/- 52 mU/ml (mean +/- coefficient of variation percentage) that was followed by a paradoxical rapid drop 2 to 4 days after the phlebotomy while the animals were still very anemic (Hb = 4.3 +/- 15 g/dl). The rapid drop in plasma EPO level could not be explained by the up-regulated clearance (clearance increased by a factor of less than 2.5) or by physiological adaptation (no change in p50, p > 0.05, second phlebotomy to Hb = 3g/dl inadequately stimulated the EPO production). The PK/pharmacodynamic (PD) analysis supports the hypothesis of a limited sustained high EPO production rate in acute anemia, which indicates an apparent deficiency in the regulation of EPO production in acute anemia. The hypothesis was supported by a PK/PD feedback inhibition model that showed good agreement with the data (r = 0.973 +/- 1.57).

A differential pharmacokinetic analysis of the erythropoietin receptor population in newborn and adult sheep.

Strong evidence indicates that erythropoietin (Epo) is eliminated via Epo receptors (EpoR). Epo receptors may be classified as erythropoietic receptors that are largely located on erythroid progenitor cells in the bone marrow (BM) and nonerythropoietic receptors present in most tissues. Epo's elimination kinetics was studied using a very sensitive tracer interaction method (TIM) before and after chemical ablation of BM as an indirect way of evaluating the EpoR through an assortment of pharmacokinetic parameters (VM, KM, K, and CL) used in differentiating the EpoR population in newborn and adult sheep. TIM identified a parallel nonlinear Michaelis-Menten (VM and KM), and linear (K) elimination pathway and found the latter pathway to be significantly (p < 0.01) more dominant in lamb: K/(VM/KM + K) = 0.309 (25.3) versus 0.0895 (18.4) mean (CV%) lambs versus adult sheep. The significantly (p < 0.01) larger total clearance found for lambs indicates a larger nonhematopoietic tissue clearance of Epo (CL = 118 (10.9) ml/h/kg versus 67.8 (19.3) lamb versus adult sheep). The VM/KM ratio for the nonlinear pathway was not found to be significantly different (p > 0.05) between newborn and adults with values of 1.10 (15.8) and 1.30 (3.81) h-1, respectively. We proposed the hypothesis that the linear pathway is via nonhematopoietic EpoR. Assuming that Epo's elimination largely depends not only on erythropoietic EpoR but also on nonhematopoietic EpoR, this work shows a significant difference in the relative proportions of the two EpoR populations in lamb and adult sheep. The larger dominance of the nonhematopoietic EpoR in lamb supports the hypothesis that these receptors are more needed in early life, e.g., providing neuroprotection from perinatal hypoxemic-ischemic episodes.

An integrated pharmacodynamic analysis of erythropoietin, reticulocyte, and hemoglobin responses in acute anemia.

PURPOSE: To determine by pharmacodynamic (PD) analysis physiologically relevant parameters of the cellular kinetics of erythropoiesis in acute anemia. METHODS: The PD relationships among erythropoietin (EPO), reticulocyte, and RBC (Hb) responses were investigated in young adult sheep in acute anemia induced twice by two controlled phlebotomies separated by a 4-week recovery period. RESULTS: The phlebotomies resulted in rapid increases in plasma EPO, with maximal levels occurring at 3 to 8 days, followed by a reticulocyte response with a delay of 0.5 to 1.5 days. The Hb returned to prephlebotomy base line at the end of the 4-week recovery period. The EPO, reticulocyte count, and Hb responses were well described by a PK/PD model (r = 0.975) with the following cellular kinetics parameters: the lag time between EPO activation of erythroid progenitor cells and reticulocyte formation; the reticulocyte-to-RBC maturation time; the reticulocyte and Hb formation efficacy coefficients, quantifying EPO's efficacy in stimulating the formation of reticulocytes and Hb, respectively; the C50 PK/PD transduction parameter defined as the EPO level resulting in half the maximum rate of erythropoiesis. CONCLUSION: Physiologically relevant cellular kinetics parameters can be obtained by an endogenous PK/PD analysis of phlebotomy data and are useful for elucidating the pathophysiologic etiology of various anemias.

Changes in erythropoietin pharmacokinetics following busulfan-induced bone marrow ablation in sheep: evidence for bone marrow as a major erythropoietin elimination pathway.

The contribution of the bone marrow to in vivo erythropoietin (EPO) elimination was evaluated by determining EPO pharmacokinetic (PK) parameters in five adult sheep in a paired manner before and after chemotherapy-induced marrow ablation. After busulfan-induced bone marrow ablation, EPO PK demonstrated progressive decreases in plasma clearance (CL), elimination half-life [t1/2(beta)], and volume of distribution at steady state (Vss) with concomitant increases in mean residence time (MRT). Eight days after beginning busulfan treatment, there were no further changes in CL, t1/2(beta), MRT, and Vss. Only 20% of baseline CL remained by day 8. The volume of distribution (Vc) and distribution half-life [t1/2(alpha)], in contrast, remained unchanged from baseline. White blood cell counts and reticulocytes gradually declined after the start of marrow ablation. Examination of bone marrow core biopsy samples obtained on day 10 revealed less than 10% of baseline marrow cellularity. No colony-forming unit erythroid (CFU-E) colonies were found after 6 days of incubation for bone marrow aspirates drawn at days 8 and 13 following busulfan treatment, whereas pre-busulfan aspirates yielded 29 CFU-E colonies per 10(5) cells in CFU-E cultures. Treatment of a sheep with 5-fluorouracil showed changes in PK parameters that were similar to the results from treatment with busulfan. The present study indicates that the bone marrow significantly contributes to the elimination of EPO in vivo.

Receptor-based model accounts for phlebotomy-induced changes in erythropoietin pharmacokinetics.

Previous clinical studies have demonstrated two distinctive pharmacokinetic behaviors of erythropoietin (EPO): changes in pharmacokinetics (PK) after a period of rhEPO treatment and nonlinear pharmacokinetics. The objective of this work was to study the temporal changes in EPO's PK following phlebotomy in order to propose possible mechanisms for this behavior. Five healthy adult sheep were phlebotomized on two separate occasions 4-6 weeks apart to hemoglobin levels of PK 3-4 g/dL. PK parameters were estimated from the concentration-time profiles obtained following repeated intravenous bolus PK studies using tracer doses of biologically active 125I-rhEPO. Based on the changes in clearances, a PK model was derived to provide a mechanistic receptor-based description of the observed phenomena. Phlebotomy resulted in a rapid increase in the EPO plasma concentration, which peaked at 760 +/- 430 mU/mL (mean +/- SD) at 1.8 +/- 0.65 days, and which coincided with a transient reduction in EPO clearance from prephlebotomy values, i.e., from 45.6 +/- 11.2 mL/hr/kg to 24.3 +/- 9.7 mL/hr/kg. As plasma EPO levels returned toward baseline levels in the next few days, a subsequent increase in EPO clearance was noted. EPO clearance peaked at 90.2 +/- 26.2 mL/hr/kg at 8.5 +/- 3.3 days and returned to baseline by 4-5 weeks postphlebotomy. The proposed model derived from these data includes positive feedback control of the EPO receptor (EPOR) pool. The model predicts that: 1) the initial reduction in EPO plasma clearance is due to a transient saturation of EPORs resulting from the phlebotomy-induced high EPO concentration; and 2) the EPOR pool is expandable not only to compensate for EPOR loss but also to adjust to a greater need for EPORs/progenitor cells to restore hemoglobin (Hb) concentration to normal levels.

A pharmacodynamic analysis of erythropoietin-stimulated reticulocyte response in phlebotomized sheep.

The pharmacodynamics (PD) of the reticulocyte response resulting from phlebotomy-induced erythropoietin (EPO) was investigated in adult sheep. The anemia caused by the controlled phlebotomy (Hb < 4 g/dl, t = 0) resulted in a rapid increase in EPO with peak concentrations from 200 to 1400 mU/ml at 0.5 to 3 days generating a delayed reticulocyte response with peak levels from 9.3 to 14.1% at 2.5 to 5.1 days. The PD EPO-reticulocyte relationship is well described by a simple kinetic model involving 3 relevant physiologic parameters: T(1) = lag-time (0.73 +/- 0.32 days, mean +/- S.D.), T(2) = reticulocyte maturation time (5.61 +/- 1.41 days), and k = EPO efficacy coefficient (0.052 +/- 0.048% g/dl mU/ml/day). Accordingly, 0.52% reticulocytes at 10 g/dl Hb level are generated per day at an EPO concentration of 100 mU/ml. The difference between the T(2) parameter in this study and the maturation time reported for humans may be due to interspecies differences or different technique and experimental conditions. The PD transduction appears largely linear in the observed EPO concentration range, indicating a full utilization of EPO without any significant PD saturation. Also, the EPO concentration versus time profiles resulting from the phlebotomy were similar to exogenous EPO profiles resulting from s.c. therapeutic dosing. This study supports the hypothesis that s.c. EPO dosing is more efficacious than i.v. dosing.

A comparison of nonlinear pharmacokinetics of erythropoietin in sheep and humans.

The primary mechanism of erythropoietin's (EPO) in vivo elimination and the tissue, or tissues, responsible are unknown. Previous studies indicating that EPO pharmacokinetic (PK) behaviour is nonlinear suggest that EPO elimination takes place by a saturable mechanism. A versatile PK system analysis, the Disposition Decomposition Analysis (DDA), capable of quantification of the Michaelis-Menten parameters, V(m) and k(m) was used to analyze and compare EPO's PK behaviour in newborn sheep and preterm infants. Lambs and infants both demonstrated nonlinear PK behaviour appropriately analyzed with DDA. Compared to preterm infants, lambs had significantly greater (p<0.05) elimination capacity as determined by the V(m) (2789+/-525 versus 1767+/-250 mU/mL per h (mean+/-S.E.), respectively), and larger extrapolated linear clearances (116+/-19.1 versus 21.3+/-1.75 mL/kg per h, respectively) (p<0.01). Lambs also demonstrated significantly larger (p<0.01) degrees of nonlinearity as judged by smaller mean k(m) values (2142+/-258 versus 6796+/-1.007 mU/mL, respectively). Of note, although the DDA does not distinguish what the mechanism of EPO elimination is, enzymatic degradation and receptor-mediated cellular internalization are two possibilities. The in vivo DDA-derived k(m) values were similar to reported in vitro binding affinity k(d) data for erythroid progenitors and cell lines having EPO-R's, i.e. 240-2400 mU/mL. The present study's demonstration that EPO's nonlinear PK behaviour in both sheep and humans can be analyzed by the DDA methodology indicates that the sheep model may be used in invasive studies needed to further characterize the mechanism of EPO elimination.

Correction for non-ideal tracer pharmacokinetic disposition by disposition decomposition analysis (DDA).

PURPOSE: Pharmacokinetic (PK) studies assume that the tracer's PK is equivalent to the parent compound. This assumption is often violated. The aim of this work is to present a method enabling the ideal tracer PK, i.e. the PK of the parent compound, to be predicted from the non-ideal tracer. METHODS: The procedure uses a disposition decomposition-recomposition (DDR) that assumes that the labeling mainly changes the elimination kinetics while the distribution kinetics is not significantly affected. In the DDR procedure an elimination rate constant correction factor (kCOR) is determined from a simultaneously fitting to plasma concentration data resulting from an i.v. injection of both the tracer and the parent compound. The correction factor is subsequently used to predict the ideal tracer PK behavior from the disposition function (i.v. bolus response) of the non ideal tracer. RESULTS: The DDR method when applied to plasma level data of erythropoietin (r-HuEPO) and its iodinated tracer (125I-r-HuEPO) from a high (4000U/kg) and a low (400U/kg) dosing of r-HuEPO in newborn lambs (n=13) resulted in excellent agreements in the elimination rate corrected dispositions in all cases (r=0.995, SD=0.0095). The correction factor did not show a dose dependence (p > 0.05). The correction factors were all larger than 1 (kCOR=1.94, SD=0.519) consistent with a reduction in the EPO elimination by the iodination labeling. CONCLUSIONS: The DDR tracer correction methodology produces a better differentiation of the PK of endogenously produced compounds by correcting for the non-ideal PK behavior of chemically produced tracers.

A tracer interaction method for nonlinear pharmacokinetics analysis: application to evaluation of nonlinear elimination.

A drug tracer is most commonly applied to get information about the pharmacokinetics (PK) of a drug that is not confounded by an endogenously produced drug or an unknown drug input. An equally important use of tracers that has not been fully recognized is their use in the study of nonlinear PK behavior. In the present study a system analysis is applied to examine the interaction between drug molecules characteristic and intrinsic to any nonlinear process which enables the nonlinearity to be identified and modeled using a drug tracer. The proposed Tracer Interaction Methodology (TIM) forms a general developmental framework for novel methods for examining nonlinear phenomena. Such methods are potentially much more sensitive and accurate than previous methods not exploiting the tracer principle. The methodology proposed is demonstrated in a simulation study and with real data in a specific implementation aimed at determining the Michaelis-Menten (MM) parameters of nonlinear drug elimination while accounting for drug distribution effects. The simulation study establishes that the TIM-based, MM parameter evaluation produces substantially more accurate parameter estimates than a nontracer (NT) conventional method. In test simulations the accuracy of the TIM was in many cases an order of magnitude better than the NT method without evidence of bias. The TIM-based, MM parameter estimation methodology proposed is ideally suitable for dynamic, non-steady-state conditions. Thus, it offers greater applicability and avoids the many problems specific to steady state evaluations previously proposed. TIM is demonstrated in an evaluation of the nonlinear elimination behavior of erythropoietin, a process that likely takes place via receptor-based endocytosis. Due to its high sensitivity, accuracy, and intrinsic nonlinearity the TIM may be suitable for in-vivo studies of receptor binding of the many biotechnology produced peptide drugs and endogenous compounds displaying receptor-mediated elimination.

Intravenous iron supplementation effect on tissue iron and hemoproteins in chronically phlebotomized lambs.

Chronic phlebotomy is an important mechanism of iron loss in premature infants. We studied inter- and intraorgan iron allocation in 10 twin lamb pairs undergoing an acute 40-50% reduction in red cell volume followed by smaller intermittent phlebotomies over an 11-day period. One twin received no supplemental iron sucrose, while the other received an average daily intravenous dose of iron sucrose of either 1 (n = 3), 2 (n = 3), 5 (n = 3), or 15 (n = 1) mg.kg-1.day-1. The total iron content of the red blood cells, liver, skeletal muscle, heart, and brain was directly related to iron dose up to 2 mg.kg-1.day-1. Tissue iron concentrations remained stable until liver iron was < 200 g/g dry wt, after which iron was preferentially directed to red blood cells over skeletal muscle, heart, and brain. Hemoprotein concentrations decreased proportionately to tissue iron, except myocardial cytochrome c, which remained preserved. Any available iron in phlebotomized, rapidly growing lambs is preferentially directed to red blood cells, and lambs require iron supplementation to maintain tissue iron and hemoprotein concentrations. A decrease in nonheme tissue iron results in the high prioritization of iron among iron-containing proteins.