Antibody-mediated Pure Red Cell Aplasia Research Articles

Erythropoietin‐induced, antibody‐mediated pure red cell aplasia*

Pure red cell aplasia (PRCA) is a rare haematological condition that is characterized by severe aregenerative anaemia due to an almost complete cessation of red blood cell production. While antibody-mediated PRCA was extremely rare before 1998, the incidence of this disorder increased sharply after 1998 in patients receiving subcutaneous epoetin alfa produced by Ortho-Biotech and marketed outside the USA. The diagnosis of antibody-mediated PRCA relies mostly on the results of bone marrow biopsy or aspirate, which shows an absence of erythroid precursors and/or red cell maturation arrest while counts of white cell and platelet precursors are normal, and on the identification of circulating anti-erythropoietin antibodies. Retrospective analysis of PRCA cases has shown that immunosuppressive therapy can induce a disappearance of anti-erythropoietin antibodies in most patients. Eur J Clin Invest 2005; 35 (Suppl. 3): 95-99.

What is antibody-mediated pure red cell aplasia (PRCA)?

What is antibody-mediated pure red cell aplasia (PRCA)?

Factors influencing the immunogenicity of therapeutic proteins

Several diseases and disorders are treatable with therapeutic proteins, but some of these products may induce an immune response, especially when administered as multiple doses over prolonged periods. Antibodies are created by classical immune reactions or by the breakdown of immune tolerance; the latter is characteristic of human homologue products. Many factors influence the immunogenicity of proteins, including structural features (sequence variation and glycosylation), storage conditions (denaturation, or aggregation caused by oxidation), contaminants or impurities in the preparation, dose and length of treatment, as well as the route of administration, appropriate formulation and the genetic characteristics of patients. The clinical manifestations of antibodies directed against a given protein may include loss of efficacy, neutralization of the natural counterpart and general immune system effects (including allergy, anaphylaxis or serum sickness). An upsurge in the incidence of antibody-mediated pure red cell aplasia (PRCA) among patients taking one particular formulation of recombinant human erythropoietin (epoetin-alpha, marketed as Eprex(R)/Erypo(R); Johnson & Johnson) in Europe caused widespread concern. The PRCA upsurge coincided with removal of human serum albumin from epoetin-alpha in 1998 and its replacement with glycine and polysorbate 80. Although the immunogenic potential of this particular product may have been enhanced by the way the product was stored, handled and administered, it should be noted that the subcutaneous route of administration does not confer immunogenicity per se. The possible role of micelle (polysorbate 80 plus epoetin-alpha) formation in the PRCA upsurge with Eprex is currently being investigated.

Antibody-Mediated Pure Red Cell Aplasia Due to Epoetin Alfa During Antiviral Therapy of Chronic Hepatitis C

Anemia frequently complicates the treatment of chronic hepatitis C with interferon and ribavirin (RVN), requiring dose reduction and jeopardizing sustained virologic response. Increasingly, epoetin alfa is used to prevent anemia in this setting. Below, we report the first case of pure red cell aplasia (PRCA) in a patient with chronic hepatitis C who received epoetin alfa (Procrit) to manage anti-viral treatment-induced anemia. Red blood cell transfusion-dependence developed 16 wk after the patient was started on peginterferon alfa-2b and RVN for chronic hepatitis C despite the simultaneous administration of epoetin alfa and subsequent discontinuation of the antiviral medications. Bone marrow biopsy was consistent with PRCA. High-titer erythropoietin antibodies, assayed by two methods, appeared shortly after epoetin alfa was administered, and were associated with a decline in serum erythropoietin to undetectable levels. Erythropoietin antibodies directed toward epoetin alfa were shown to cross react with darbepoetin alfa (Aranesp), and a neutralization assay confirmed that they inhibited cell growth in the presence of erythropoietin. Transfusion-dependence resolved approximately 16 wk after discontinuing epoetin alfa, and 6 wk after starting danazol. PRCA caused by the development of erythropoietin antibodies is a potentially life-threatening complication of administering epoetin alfa to prevent the anemia associated with antiviral therapy in patients with chronic hepatitis C.

Current and future challenges in anaemia management

The introduction of recombinant human erythropoietin (rhEPO; epoetin) nearly 20 years ago revolutionized the management of renal anaemia. The correction of anaemia with epoetin is associated with improvements in the quality of life of patients with chronic kidney disease (CKD), and reductions in morbidity and mortality. In this supplement, the authors present an overview of pertinent issues in renal anaemia management that were tackled during two satellite symposia held on June 9 and 10, 2003 at the World Congress of Nephrology in Berlin, Germany: ‘Current and future challenges in anaemia management’ and ‘Who wants to defeat anaemia? An interactive insight into anaemia management today’. All recombinant human proteins can potentially induce an immune response, especially when administered repeatedly over prolonged periods. A multitude of factors, including structural properties, storage and handling, contaminants and impurities, administration and formulation, may affect immunogenicity. In recent years, a peak was noted in the number of cases of pure red cell aplasia (PRCA) associated primarily with one particular epoetin-a product available outside of the USA, Eprex /Erypo . As a result, regulatory authorities in Europe restricted the administration of this product to the intravenous (i.v.) route. Currently there is no evidence for an increasing trend in antibody-mediated PRCA for this or other epoetin formulations. The optimal route of epoetin administration has been explored in numerous studies. Current European Best Practice Guidelines and K/DOQI Guidelines on renal anaemia management recommend subcutaneous (s.c.) administration as the preferred route for epoetin in CKD patients not on dialysis, in haemodialysis, peritoneal dialysis and transplanted patients, when not contraindicated. These recommendations take into account the efficacy, frequency of dosing, cost and convenience of epoetin treatment, alongside the safety and tolerability of specific products. Target haemoglobin (Hb) levels can be maintained with much lower doses of epoetin when administered by the s.c. route. Clearly, therefore, s.c. administration of epoetin is associated with economic advantages in terms of direct drug cost and may also provide cost benefits by relieving the burden on health care services. In the case of epoetin-b, s.c. administration allows for reduced dosing frequencies at once weekly and even once every 2 week intervals during the maintenance phase of treatment in stable peritoneal dialysis patients, without compromising safety or efficacy. Reduced dosing frequency and the availability of a pen device, specifically designed for the self-administration of s.c. epoetin-b, should increase patients’ readiness to self-administer treatment and should facilitate the early initiation of anaemia treatment in patients with CKD not yet requiring dialysis. Anaemia contributes to the progression of cardiovascular disease. Detrimental effects begin at an early stage of CKD, well before kidney function deteriorates to the point when dialysis is required. Indeed, low Hb is an independent risk factor for left ventricular (LV) growth in CKD patients not needing dialysis, as well as in patients receiving dialysis, and in those who have undergone renal transplantation. Data suggest that management of anaemia can significantly reduce the cardiovascular risks associated with CKD; early correction of anaemia may be especially important in improving patient outcomes. The ability of epoetin to reverse changes in LV geometry may be limited in patients with advanced renal and cardiac disease. In this regard, the ongoing Cardiovascular risk Reduction by Early Anaemia Treatment with Epoetin b (CREATE) study, which is investigating the benefits of early, complete anaemia correction with epoetin-b on cardiovascular events in patients with CKD not receiving renal replacement therapy, will provide important information. The risk of developing cardiovascular disease is even higher in patients with CKD who also have diabetes. Diabetes is now the most common primary diagnosis associated with end-stage renal disease (ESRD), and a Correspondence and offprint requests to: Professor Eberhard Ritz, Department of Internal Medicine, Bergheimer Str. 56a, D-69115 Heidelberg, Germany. Email: Prof.E.Ritz@t-online.de

The increased incidence of pure red cell aplasia with an Eprex formulation in uncoated rubber stopper syringes

The incidence of pure red cell aplasia (PRCA) in chronic kidney disease patients treated with epoetins increased substantially in 1998, was shown to be antibody mediated, and was associated predominantly with subcutaneous administration of Eprex. A technical investigation identified organic compounds leached from uncoated rubber stoppers in prefilled syringes containing polysorbate 80 as the most probable cause of the increased immunogenicity. This study investigated whether the incidence of PRCA was higher for exposure to the product form containing leachates than for leachate-free product forms. Antibody-mediated PRCA cases were classified according to indication, product form, and route of administration. Exposure estimates were obtained by country, indication, route of administration, and product form. For 2001 to 2003, the PRCA incidence rate for patients with subcutaneous exposure to Eprex in prefilled syringes with polysorbate 80 and uncoated rubber stoppers (leachates present) was 4.61/10,000 patient years (95% CI 3.88-5.43) versus 0.26/10,000 patient years (95% CI 0.007-1.44) for syringes with coated stoppers (leachates absent). The rate difference was 4.35/10,000 patient years (95% CI 3.44-5.26; P < 0.0001); the rate ratio was 17 (95% CI 3.14-707). A substantial rate difference remained in sensitivity analyses that adjusted for exposure to multiple product forms. The epidemiologic data, together with the chemical and immunologic data, support the hypothesis that leachates from uncoated rubber syringe stoppers caused the increased incidence of PRCA associated with Eprex. Currently, all Eprex prefilled syringes contain fluoro-resin coated stoppers, which has contributed to decreased incidence of PRCA with continued surveillance.

Antibody-mediated pure red cell aplasia (PRCA): epidemiology, immunogenicity and risks

Although epoetin-induced antibody (Ab)-mediated pure red cell aplasia (PRCA) was very rare prior to 1998, a large increase in the number of global cases was observed from 1999 to 2002 in patients treated with erythropoiesis-stimulating agents (ESAs) for the anaemia associated with chronic kidney disease (CKD). The number of global cases of this immunological form of PRCA has declined precipitously since 2003 following increased awareness of this disorder and changes in the handling and administration of the formulation of epoetin-alpha (EPO) that was associated with the majority of cases. Current recommendations state that patients should stop treatment immediately following a diagnosis of Ab-mediated PRCA and not resume treatment with the same or another ESA. The feasibility of re-treatment following remission from PRCA or during ongoing immunosuppressive therapy is currently under investigation. The immunological mechanism for developing Ab-mediated PRCA is unknown, but a variety of factors may increase the immunogenicity of epoetin or other ESAs. Product-related factors that have the potential to impact on immunogenicity include sequence variations in proteins, the degree and nature of protein glycosylation, the manufacturing process, handling and storage, and components and properties of the product formulation. Patient-related factors associated with developing Ab-mediated PRCA include skin reactions, immune status and treatment history. Increased awareness among physicians of the factors contributing to the development of PRCA and its distinguishing clinical features has coincided with studies aimed at identifying effective therapies for this disorder. A number of immunosuppressive therapies have been shown recently to reconstitute effectively the erythropoietic response in patients with PRCA. However, therapeutic approaches for this serious immunological reaction to recombinant ESAs remain investigative.

Assays for detecting and diagnosing antibody-mediated pure red cell aplasia (PRCA): an assessment of available procedures

Antibody (Ab)-mediated pure red cell aplasia (PRCA) develops when patients mount a neutralizing Ab response to recombinant erythropoiesis-stimulating agents (ESAs) such as epoetin-alpha (EPO). These neutralizing Abs can also cross-neutralize endogenous EPO, leading to a state of absolute EPO resistance and transfusion dependence. The diagnosis of Ab-mediated PRCA in part relies on the sensitive and specific detection of serum anti-EPO Abs and a confirmatory examination of patients' bone marrow for lack of erythroid precursors. To date, a variety of assays have been used to detect anti-EPO Abs, including radioimmunoprecipitation (RIP) assay, enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR) and bioassays that measure neutralizing Abs. Each of these assays can yield informative results and possess characteristic benefits and limitations, so it is unclear whether or not a "superior" assay is required or possible. To date, a universal standardized assay has not yet been established that would facilitate the comparison of Ab data derived from different laboratories and retrospective analysis of stored sera. This review evaluates the results of studies measuring anti-EPO Abs with different assays and compares their relative advantages and disadvantages in terms of specificity, sensitivity, ease of use and ability to measure Ab-binding affinities and subclasses. These comparisons provide a basis for determining the optimal assay(s) for screening and/or analysis of patients' serum for anti-EPO Abs during treatment or after onset of Ab-mediated PRCA.

Antibody-mediated pure red cell aplasia (PRCA): ensuring future progress by collecting data from a registry

The recent emergence of antibody (Ab)-mediated pure red cell aplasia (PRCA) resulting from administration of certain erythropoiesis-stimulating agents (ESAs) has heightened awareness of the potential for this disorder in patients receiving ESAs for anaemia associated with chronic kidney disease (CKD). The Spanish Society of Nephrology sponsored an independent registry for analysis of patients who developed epoetin-induced, Ab-mediated PRCA in Spain. Twelve patients from 11 regional hospitals were included in the Spanish PRCA registry from November 2000 to December 2002 that met the criteria for Ab-mediated PRCA. Patients were reported using a standardized form specifically developed for PRCA, and serum samples were analysed in a central laboratory at Reina Sofia University Hospital in Cordoba, Spain. The characteristics of these patients, their serological and haematological results, and the outcomes of immunosuppressive therapies are presented. The Spanish PRCA registry serves as a model for establishing an independent global PRCA registry sponsored by the various nephrology societies in European Union countries, and elsewhere and coordinated by key investigators from the respective countries.

Antibody-mediated pure red cell aplasia (PRCA) treatment and re-treatment: multiple options

In the vast majority of patients with antibody (Ab)-mediated pure red cell aplasia (PRCA), simple withdrawal of the erythropoiesis-stimulating agent (ESA) does not effectively reverse PRCA. In contrast, immunosuppressive treatments can induce the disappearance of anti-erythropoietin Abs and a reversal of PRCA. Consensus opinion on the optimal therapy has not been established, but individual case reports or case series suggest that kidney transplantation or treatment with corticosteroids plus cyclophosphamide are the most effective therapies. However, treatment with cyclosporine is an interesting alternative, since it appears to be effective in at least two-thirds of patients and with minimal side effects. Due to the key role of ESAs in the management of patients with chronic kidney disease (CKD), some patients have been re-treated with an ESA following resolution of Ab-mediated PRCA. In all reported cases, this treatment increased haemoglobin levels, alleviated the need for transfusions and did not have side effects. However, one should be extremely cautious when deciding to re-treat a patient with ESA, due to the small number of reported cases and the possibility of publication bias.

What is antibody-mediated pure red cell aplasia (PRCA)?

Antibody (Ab)-mediated pure red cell aplasia (PRCA) is an immunological pathology associated with the production of neutralizing Abs that inhibit the erythropoietic activity of endogenous erythropoietin (EPO) and recombinant erythropoiesis-stimulating agents (ESAs). Although this disorder occurs very rarely, the number of reported cases has increased dramatically in recent years, predominantly in patients with chronic kidney disease (CKD)-associated anaemia receiving subcutaneous (s.c.) injections of one particular formulation of recombinant epoetin-alpha. This disorder is differentiated from classic forms of PRCA that are caused by chemical toxaemia (i.e. erythroblastopenia induced by chemical compounds), lymphoproliferative neoplasms, thymoma, human parvovirus B19 and certain autoimmune disorders. Patients with Ab-mediated PRCA develop resistance to EPO and severe anaemia that follows a period of successful erythropoietic response, and exhibit characteristic decreases in blood haemoglobin (Hb) level and in the number of circulating reticulocytes. However, it is not yet possible to predict which patients will develop PRCA or when in the course of their treatments PRCA may develop. Laboratory confirmation of Ab-mediated PRCA requires bone marrow examination demonstrating few or no erythroid precursors and the presence of serum anti-EPO Abs using a validated assay. These neutralizing anti-EPO Abs recognize the protein core of the EPO molecule; carbohydrate groups on EPO can affect the binding of Abs but are themselves not immunological determinants. Animal models are being developed to increase further our understanding of the immunological mechanisms underlying the onset and progression of Ab-mediated PRCA.

Epoetin-associated pure red cell aplasia in patients with chronic kidney disease: solving the mystery

A substantial increase in the incidence of pure red cell aplasia (PRCA) associated with recombinant human erythropoietin (epoetin) treatment occurred in 1998. The upsurge of antibody-mediated PRCA was almost exclusively associated with chronic kidney disease patients who received subcutaneous epoetin therapy and the formulation of epoetin-alpha distributed outside the USA (EPREX/ERYPO). A systematic programme of technical, immunological and epidemiological investigations was initiated to identify the possible causes. The potential causes were evaluated on the basis of the following criteria: temporal correlation with the increase in incidence of PRCA, significant difference between EPREX/ERYPO and other epoetin products, sufficient concentration in the product to elicit a weak immune response, evidence of immunogenic activity in animals supportive, and consistent with available clinical data. Organic compounds that were leached from rubber stoppers through the action of polysorbate 80 were detected in pre-filled syringes with uncoated rubber stoppers containing polysorbate 80-formulated EPREX/ERYPO (introduced outside the USA in 1998). The leachates were not present when the stoppers were coated, in the product formulated with human serum albumin or in other epoetin products. The adjuvant activity of the leachates was demonstrated in mice. The incidence of PRCA was significantly higher in patients exposed to the polysorbate 80 formulation of epoetin-alpha delivered from pre-filled syringes with uncoated rubber stoppers, which were recalled in 2003, than in patients exposed to the same formulation from syringes with coated rubber stoppers. In conclusion, these data strongly suggest that leachates were the critical contributory factor in the increased incidence of antibody-mediated PRCA attributed to EPREX/ERYPO.

Re-importation of pharmaceuticals may be unsafe: Lessons learned from the RADAR assessment of erythropoietin (EPO)-associated pure red cell aplasia (PRCA)

2512 Background: Recombinant human erythropoietin (EPO) has been a breakthrough in cancer- and renal insufficiency-associated anemia since 1988. Antibody-mediated PRCA is a rare, serious toxicity characterized by severe anemia and neutralizing antibodies to EPO. Methods: The Research on Adverse Drug events And Reports (RADAR) project reviewed all suspected (n=448) and antibody-confirmed cases of PRCA reported worldwide from 1988 to Oct 2003. Results: Among 208 confirmed cases, median age was 66 (range, 14–86), male to female ratio was 2.4:1, median time from EPO initiation to PRCA suspicion was 9.4 months, and reports varied according to geography [Europe (58%), Asia (19%), Canada (13%), Australia (7%), and USA (3%)]; type of EPO used (EPO alpha alone, 81% and EPO alpha plus EPO beta, 16%); administration route (subcutaneous 97%); and year {incidence: pre-1998, 3 cases per million patient-years (MPY) and post-1998 [Australia (64 MPY), France (48 MPY), England (57 MPY), Canada (46 MPY), Spain (37 MPY), Italy (8 MPY), and Germany (7 MPY)]. 97% of cases were associated with Eprex brands. Reporting according to 4 milestones was evaluated: FDA approval in 1988 to Human Serum Albumin (HSA) removal from Eprex in Europe and Canada (1998; T1); from HSA removal to the first warning about PRCA from its manufacturer in 2001 (T2); to the second sponsor warning recommending a change from SC to IV administration in 2002 (T3), to the packet insert for Eprex brands of EPO contraindicating SC use for renal patients (T4), to Oct 2003 (T5), with variations according to country. In the more recent time periods, Canada had the highest incidence. Conclusions: EPO-associated PRCA remains an international concern, especially in Canada. Re-importation of Eprex products from Canada may allow for this severe complication to occur in the U.S. No significant financial relationships to disclose.

Evaluation of Methods to Detect and Characterize Antibodies against Recombinant Human Erythropoietin

Background: From May 1998 to November 2000, 13 European patients developed antibody-mediated pure red cell aplasia during treatment with recombinant human erythropoietin (rHuEPO), reinforcing the need for analytical testing for antibodies against erythropoietic agents. Specimens from 8 patients were provided for further antibody testing and characterization. Methods: We evaluated 4 analytical methods with these sera: radioimmune precipitation (RIP), enzyme-linked immunosorbent assay (ELISA), biosensor immunoassay, and a bioassay for identification of neutralizing antibodies. Results: The RIP, biosensor immunoassay, and biological assay performed equally to detect and quantify anti-rHuEPO antibodies. The ELISA failed to detect antibodies in 2 patient samples. The biosensor immunoassay could determine antibody isotypes, subclasses, and dissociation rates and the bioassay could determine whether these antibodies were able to neutralize the biological effect of the drug; the other assays could not make this determination. Conclusion: We recommend the use of the biosensor immunoassay followed by a bioassay to best identify and characterize anti-rHuEPO antibodies. The biosensor immunoassay allows for identification of all classes and subclasses of immunoglobulins and is a preferred method for the identification of lower-affinity antibodies. The bioassay is needed to determine if the antibodies identified have the capacity to neutralize a biological effect of the drug in a cell-based system.

Pure red cell aplasia with anti-erythropoietin antibodies occurs more commonly with one formulation of epoetin alfa than another

SUMMARYObjective: To compare rates of pure red cell aplasia (PRCA) over time in patients with chronic renal failure treated with subcutaneous injections of two brands of epoetin alfa (either Eprex or Epogen) or epoetin beta (NeoRecormon).Methods: Cases of antibody-mediated PRCA associated with epoetin alfa-treated patients were obtained from public databases and company websites and limited to time periods when exposure data also were available The subcutaneous exposure rates per 100000 patient-years were calculated for the periods 1989-1998and 1999-2002.Results: The event rate for antibody-mediated PRCA for Epogen and Eprex were similar from 1989 to 1998, but the number of cases of Eprex-associated PRCA has increased markedly since 1999, even after accounting for subcutaneous exposure. In contrast, rates have remained low for Epogen and NeoRecormon.Conclusions: The recent increase in PRCA appears to be product specific and cannot be explained solely as a consequence of increased use of the subcutaneous route of administration.

Pure red cell aplasia and anti-erythropoietin antibodies in patients treated with epoetin.

Recombinant human erythropoietin (epoetin) was first used for the treatment of renal anaemia in 1986. During the first 10 years of its use, epoetin-induced antibodies were a rare complication and only three cases of patients with epoetin-induced antibodies associated with pure red cell aplasia (PRCA) were published. Since 1998, however, there has been a significant increase in the number of patients developing severe anaemia during the course of epoetin treatment due to neutralizing antibodies. Patients with PRCA present with an absolute resistance to epoetin therapy and then rapidly develop severe anaemia with a very low reticulocyte count (<10 000/mm(3)). Consequently, patients become dependent on blood transfusions to maintain an acceptable level of haemoglobin. By December 2002, approximately 142 patients worldwide had been diagnosed with antibody-positive PRCA after receiving epoetin. The vast majority of these patients had been treated with the Eprex/Erypo brand of epoetin alfa, but there were also some cases in which patients had been receiving epoetin beta (NeoRecormon). To date, there have been no cases of antibody-mediated PRCA reported with the sole use of darbepoetin alfa (Aranesp). All patients with epoetin-induced anti-erythropoietin antibodies had received the drug subcutaneously (s.c.), and almost all had chronic kidney disease-related anaemia. To our knowledge, no patient treated exclusively by intravenous (i.v.) administration has developed anti-erythropoietin antibodies. The increase in reported cases coincides with the removal of human serum albumin from the ex-US formulation of epoetin alfa, in order to comply with new regulations from the European regulatory authorities. It has been proposed that the new formulation is less stable, allowing aggregates of erythropoietin molecules to form, which increases the probability of antibody formation. Treatment with epoetin must be discontinued if PRCA is suspected. Patients do not respond to an increase in dose. Furthermore, patients must not be switched to another form of erythropoietic therapy as the antibodies cross-react with all erythropoietic therapies available. In around 70% of cases, immunosuppressive regimens are effective in eliminating the antibodies; cessation of epoetin therapy without concomitant immunosuppression is rarely effective. Kidney transplantation seems to provide an immediate and effective cure.

Darbepoetin alfa: a novel erythropoiesis-stimulating protein.

Darbepoetin alfa is a novel erythropoiesis-stimulating protein developed for the treatment of anemia. It is a hyperglycosylated analog of recombinant human erythropoietin with the same mechanism of action as erythropoietin, but with a three-fold longer terminal half-life after intravenous administration than recombinant human erythropoietin and the native hormone both in animal models and in humans. Clinical studies in patients with chronic renal failure either receiving or not receiving dialysis have shown that darbepoetin alfa is equivalent to recombinant human erythropoietin in terms of increases in hemoglobin concentration, percentage of patients achieving target hemoglobin concentration and average time to reach target hemoglobin concentration, although darbepoetin alfa is administered less frequently (once weekly or every other week). Clinical trials in cancer patients either receiving or not receiving chemotherapy have demonstrated that darbepoetin alfa is safe and effective in alleviating anemia at dose intervals of once every 1, 2 or 3 weeks, and results suggest that it may achieve greater and more rapid responses than recombinant human erythropoietin in cancer patients. Furthermore, an improvement in health-related quality of life has been observed in association with anemia correction using darbepoetin alfa therapy in these patients. Darbepoetin alfa has been approved for intravenous and subcutaneous administration by the European Commission and the FDA for the treatment of anemia in patients with chronic renal failure. Additionally, this product was recently approved by the FDA for the treatment of anemia in patients with nonmyeloid malignancies where anemia is due to the effect of concomitantly administered chemotherapy. The recommended starting dose in chronic renal failure patients is 0.45 microg/kg once weekly for both intravenous and subcutaneous administration, with subsequent titration based on the hemoglobin concentration. In cancer patients, the recommended starting dose is 2.25 microg/kg once weekly by subcutaneous injection and subsequent titration. The adverse event profile of darbepoetin alfa is similar to that of recombinant human erythropoietin in both settings. There are no reports of antibody formation associated with darbepoetin alfa in chronic renal failure patients, and three cases of antibody formation, with neutralizing activity in one of the cases, have been reported in cancer patients. However, no cases of antibody-mediated pure red cell aplasia have been reported. The longer half-life of darbepoetin alfa, together with a similar efficacy and safety profile, confers the clinical advantage over recombinant human erythropoietin of allowing a less frequent dosing (once weekly or every other week versus one to three times weekly in renal patients), thus reducing health-care utilization and probably improving patient compliance.

Pure red cell aplasia.

Pure red cell aplasia.

Gamma Globulin for Antibody-Mediated Pure Red-Cell Aplasia

Gamma Globulin for Antibody-Mediated Pure Red-Cell Aplasia

Antibody-mediated Pure Red Cell Aplasia with Erythropoietic Maturation Arrest: in vitro studies on the etiology

Antibody-mediated Pure Red Cell Aplasia with Erythropoietic Maturation Arrest: <i>in vitro</i> studies on the etiology