Ferrokinetics: a biologic model for plasma iron exchange in man.

A method is presented for calculating internal iron kinetics. An early reflux associated with extravascular exchange and a late reflux associated with erythropoiesis are described. A biologic model of iron exchange is proposed in which erythron iron turnover is divided into an effective portion (iron fixed in circulating red cells) and wastage iron of erythropoiesis (late reflux). Nonerythroid iron exchange also has a fixed portion (parenchymal uptake) and an early reflux (lymphatic circuit), both of which correlate in amount with the amount of plasma iron. Ferrokinetic measurements in normal subjects and in various pathologic states are presented to validate the model.

The anemia of chronic renal failure in sheep. Response to erythropoietin-rich plasma in vivo.

The hypoproliferative anemia in chronic renal failure has been assumed to be the result of decreased erythropoietin (Ep) production by the damaged kidney and of the shortening of erythrocyte survival. However, many in vitro studies suggest that erythropoietic inhibitors in uremic plasma may contribute to the anemia. To determine the in vivo relevance of uremic inhibitors, increasing amounts of Ep as Ep-rich plasma were infused into six uremic sheep, and their erythropoietic responses were compared with those of nine normal sheep receiving similar amounts of Ep-rich plasma. Three sheep were studied in both normal and uremic states. Ep-rich plasma was obtained from phenylhydrazine- and phlebotomy-induced anemic sheep. Stable uremia was created by subtotal nephrectomy. Erythropoiesis was quantitated by reticulocyte response, ferrokinetics (plasma iron turnover and marrow transit time), and by hemoglobin C synthesis. Ep-rich plasma stimulated erythropoiesis similarly in uremic and normal sheep, regardless of the degree of uremia. Nondialyzed uremic sheep responded as well as dialyzed animals. The anemia was corrected in the uremic dialyzed animals. The anemia was corrected in the uremic sheep after 15-40 daily infusions of Ep-rich plasma, the total dosage depending on the severity of the anemia. Polycythemia was induced when the infusions were continued. Reticulocytes, plasma iron turnover, and erythrocyte mass changes increased as the amount of Ep-rich plasma was increased. These dose-response effects, coupled with the identical erythropoietic response in normal and uremic sheep given the same amount of Ep-rich plasma, imply that there are no physiologically significant erythropoietic inhibitors in uremia.

Methods used to evaluate the quality of evidence underlying the National Kidney Foundation-Dialysis Outcomes Quality Initiative Clinical Practice Guidelines: description, findings, and implications.

This report describes the approach the National Kidney Foundation-Dialysis Outcomes Quality Initiative (NKF-DOQI) used to assess the strength of published evidence pertinent to individual NKF-DOQI Clinical Practice Guidelines, as well as the relationship between that approach and methods used by the US Preventive Services Task Force, the Cochrane Collaboration, and the Agency for Health Care Policy and Research to rate the quality and/or strength of evidence. We also present the results of an analysis of the strength of evidence underlying the NKF-DOQI Guidelines showing that one cannot infer the quality of evidence reported in a study (rated either on a 0-to-1 scale or categorically as excellent, very good, good, fair, or poor) simply by knowing the type of study design used (randomized trial, nonrandomized trial, natural experiment, cohort study, cross-sectional study, case-control study, case report). Issues related to assessment of the strength of evidence underlying a practice guideline opposed to that reported in an individual study are highlighted.

Current concepts of anemia management in chronic renal failure: impact of NKF-DOQI.

Since the introduction of recombinant human erythropoietin (rHuEPO) into clinical nephrology practice 10 years ago, there has been a slow increase in hemoglobin (Hgb) levels, but most patients with the anemia of chronic renal failure are still moderately anemic and have not achieved the target Hgb (11 to 12 g/dL) recommended by the NKF-DOQI anemia guidelines. Functional iron deficiency, insufficient rHuEPO doses and comorbid factors such as inflammation/infection have been the major reasons for not achieving this target. By optimizing iron stores with regular infusions of intravenous iron in the hemodialysis patient (who has significant blood [iron] losses related to the hemodialysis procedure), and giving adequate amounts of rHuEPO, preferably subcutaneously instead of intravenously, the NKF-DOQI recommended target Hb can be achieved in the majority of patients so treated.

Hypertension following erythropoietin therapy in anemic hemodialysis patients.

Recombinant human erythropoietin (rHuEpo) corrects the anemia of end-stage renal disease. However, hypertension has been observed as an adverse effect of increasing red cell mass. In our study, 44 of 63 patients (70%) treated with rHuEpo had an increase in mean arterial pressure greater than 10 mm Hg or required new or additional hypertensive medications. Retrospective analysis disclosed that increasing blood pressure was associated with pretreatment hematocrit level less than or equal to 0.20 (P = .05) and dependency on red cell transfusions (P less than .01). Factors not associated with hypertension included the rate of rise of the hematocrit, the net rise in hematocrit, age, sex, the number of years on dialysis, the presence or absence of kidneys, smoking, or the presence of pretreatment hypertension. Noninvasive hemodynamic studies in eight normotensive patients before and after improvement of the anemia demonstrated a normalization of the decreased peripheral vascular resistance and a reduction toward normal in the elevated cardiac output. In three of these patients, clinical hypertension subsequently evolved. Follow-up hemodynamic studies in nine other patients receiving new or additional antihypertensive medications were difficult to interpret. Although the hypertension can be controlled with routine medication, hypertensive encephalopathy may occur if the blood pressure increases rapidly when the hematocrit increases with rHuEpo therapy.

Iron overload in renal failure patients: changes since the introduction of erythropoietin therapy.

Iron overload was a common complication in patients with chronic renal failure treated with dialysis prior to the availability of recombinant human erythropoietin (rHuEPO) therapy. Iron overload was the result of hypoproliferative erythroid marrow function coupled with the need for frequent red blood cell transfusions to manage symptomatic anemia. The repetitive use of intravenous iron with or without the use of red blood cell transfusions also contributed to iron loading and was associated with iron deposition in liver parenchymal and reticuloendothelial cells; however, there were no abnormal liver function tests or evidence of cirrhosis unless viral hepatitis resulted from the transfusions. With rHuEPO therapy, the excess iron stores were shifted back into circulating red blood cells as the anemia was partially corrected, and red blood cells were lost from circulation by the hemodialysis procedure. After several years of rHuEPO therapy, most hemodialysis patients required iron supplements to replace the continuing blood losses related to hemodialysis. The potential complications of iron overload (parenchymal iron deposition, permanent organ damage, increased risk of bacterial infections, and increased free radical generation) are reviewed in the context of this setting.

Effects of erythropoietin on strength and functional status of patients on hemodialysis.

The strength, endurance, and functional status of 15 anemic (HCT 21.2 +/- 4.6) hemodialysis patients was quantified prior to the administration of erythropoietin (epoetin) and after the anemia was partially corrected (HCT 35.4 +/- 2.3). Subjects showed significant increases in strength, measured isometrically (p < .01) and isokinetically (p < .01 at four of five speeds). They also demonstrated improved endurance and rated their functional ability higher. Anemia contributes to significant debilitation in hemodialysis patients and, when reversed with epoetin therapy, results in significantly improved muscle function and endurance.

The long-term effects of recombinant human erythropoietin on the cardiovascular system.

Fifty-five hemodialysis patients (pts) received rHuEpo for 3-5 years (51 +/- 11 months, hematocrit 32.5 +/- 3.7). BP medication was required in 42% of pts prior to rHuEpo (Hct 20.8 +/- 3.5) and 69% (38 patients) now require such therapy. BP was controlled with single therapy in 16 pts and only 8 required 3 or more different BP drugs. Vascular access clotting episodes were rare in pts with autologous fistula (17 of 24 pts had no clotting), whereas access clotting episodes were 10 times more common in pts with AV grafts, yet 20% had no clotting after 3-5 years of rHuEpo. Heart size decreased in most who initially had cardiomegaly. Cardiovascular related and other deaths were decreased in this selected group when compared to other dialysis pts matched for age, race and type of renal disease.

Management of iron deficiency in renal anemia: guidelines for the optimal therapeutic approach in erythropoietin-treated patients.

Much progress has been made in recent years in the management of anemia associated with chronic and renal failure with recombinant human erythropoietin (r-Hu EPO). However, there remains much debate surrounding the diagnosis and treatment of iron deficiency. To ensure that full benefit from erythropoietin therapy is received, most patients require iron supplement during treatment. There are, however, few guidelines for the use of iron therapy. Iron deficiency results in an inadequate response to r-Hu EPO and is the main cause of resistance to this treatment. Oral iron therapy is of limited value in patients receiving r-Hu EPO. Thus, intravenous iron supplementation should be administered only in patients who do not tolerate available intravenous iron preparations or who are on continuous ambulatory peritoneal dialysis with no evidence of functional iron deficiency. This article provides guidelines for the diagnosis of absolute or functional iron deficiency in patients with renal anemia and suggests treatment schedules for intravenous iron supplementation. We hope that all dialysis patients will be able on this basis to achieve a satisfactory iron status and benefit fully from r-Hu EPO therapy.

Erythropoietin 1991--an overview.

Recombinant human erythropoietin (epoetin) is a remarkably safe and effective biological product. Many dialysis patients are benefiting from the use of this drug when administered intravenously (IV) or subcutaneously (SC) three times a week. However, many patients are not receiving optimal therapy. Optimal therapy requires an understanding of the principles of effective usage and a definition of an optimal hematocrit (Hct) level. These therapeutic principles include (1) the erythroid response to epoetin is dose-dependent, but variable within a given dose; (2) the SC route of injection is as effective, if not more so, than IV injections; (3) the frequency of administration is route-dependent; (4) adequate iron stores are necessary for optimal response; (5) blood pressure may increase as the Hct increases, but may improve with time due to hemodynamic adjustments; (6) the anemia is primarily a hormone-deficiency state and not due to uremia; and (7) infections and traumatic (ie, surgical) inflammation may blunt the response to epoetin. Many patients with the anemia of renal failure have yet to benefit from treatment. These include patients with progressive renal failure or chronic transplant rejection, and dialysis patients who have had incomplete correction of their anemia.

The future of r-HuEPO.

Since the introduction of recombinant human erythropoietin (r-HuEPO) 9 years ago, there have been tremendous physiological improvements in patients with various anaemias due to absolute and relative erythropoietin (Epo) deficiencies. However, not all patients that could benefit from r-HuEPO are being treated, not all are responding who should be responding, and most dialysis patients (who comprise the single largest group of treatment recipients) are being inadequately treated. The future of r-HuEPO will depend upon whether clinicians can optimize the use of r-HuEPO and determine what should be the optimal haematocrit. These issues will, in turn, depend upon whether three interdependent variables are addressed: the need for more scientific studies to evaluate various aspects of the use and effectiveness of r-HuEPO; the need for physician education to better understand the role of r-HuEPO in optimizing health in patients with anaemia in chronic renal failure and in the anaemia of chronic disease; and the need for less costly r-HuEPO therapy so that more patients can be treated and receive optimal therapy. Better use of r-HuEPO could result in significantly improved morbidity and perhaps improved survival of patients with Epo-deficient anemias.

Implementation of the Anemia Guidelines.

Implementation of the National Kidney Foundation-Dialysis Outcomes Quality Initiative (NKF-DOQI) Guidelines for the treatment of the anemia of chronic renal failure is a great challenge to all concerned with the improvement in the quality of life and survival of patients with chronic renal failure. These include physicians, nurses, technicians, dietitians, social workers, administrators, and private and public (Health Care Financing Administration) payers of the care. The principles of the process of implementation are reviewed and the barriers that can prevent implementation are discussed, showing how most of these can be overcome. Several of the more controversial Guidelines are discussed in detail, showing that with protocols that address the means for implementation, the goals of these Guidelines can be achieved.

Guidelines for recombinant human erythropoietin therapy.

Extensive testing has proven that recombinant human erythropoietin (r-HuEPO; EPOGEN [epoetin alfa], AMGEN Inc, Thousand Oaks, CA) corrects the anemia of end-stage renal disease and eliminates the need for transfusions in virtually all patients. Patients whose hematocrit levels are less than 0.30 or who are transfusion dependent are candidates for therapy. A dosage of 50 to 150 U/kg body weight intravenously three times a week produces an increase in hematocrit by approximately 0.01 to 0.02 per week. Once the hematocrit reaches 0.30 the dose is adjusted so that a target hematocrit of 0.32 to 0.38 is maintained. Eighty percent of patients need maintenance doses of r-HuEPO of less than or equal to 150 U/kg; the other 20% of patients require larger doses. Reasons for poor responses include iron deficiency, inflammation due to surgery or infection, and osteitis fibrosa. Most patients require iron supplementation to prevent functional iron deficiency. BP increased in one third of patients, and in 3% seizures occurred during the initial phase of therapy, often associated with a sudden increase in BP. This hypertension can be controlled with medication. Increased dialyzer clotting may occur, which is prevented when heparin doses are adjusted, and dialyzer solute clearances may decrease slightly. Treatment with r-HuEPO does not elicit an antibody response. The mechanism of action of r-HuEPO is identical to that of natural erythropoietin, and therefore is an appropriate therapy for the long-term management of anemia in chronic renal failure.

The use of recombinant human erythropoietin in humans.

Recombinant human erythropoietin (rhEPO) has now been in clinical trials for over three years. It has been shown to be nearly uniformly effective in correcting the anaemia of patients on haemodialysis or patients with progressive chronic renal failure not yet on dialysis. Preliminary results indicate that rhEPO is effective in increasing the ability of individuals to donate blood for self-use and early trials have shown the drug to increase the haematocrit in patients with rheumatoid arthritis. Trials in patients with anaemia associated with cancer or myelodysplastic syndromes are warranted. rhEPO will have a major impact as a therapeutic, particularly in patients with renal disease.