Erythropoietin concentration

Erythropoietin concentrated solution Ph.Eur. Identification Series of closely related glycoproteins na ... 

In Table 4, an overview is presented of the different experimental parameters of the CE analyses that are included in the analytical instructions part of the specific monographs mentioned above. Notice that the first 13 parameters (from capillary dimensions up to system suitability tests ) are those described in the FDA draft guidance for industry described in paragraph II From this overview it can be concluded that most experimental parameters required by the draft guidance are included in the specific monographs, currently published in the Ph.Eur. and USP. In the monograph for erythropoietin concentrated solution the injection parameters are not included. Only the injection mode (pressure or vacuum) is defined. Instead,... 

EIGURE 32.13 Correlation betwreen observed and predicted erythropoietin concentration values analyzing sparse sampling data Auth a population pharmacokinetic model (no r value given). (Reproduced wnth permission from Hayashi W et al. Br J Clin Pharmacol 1998 46 11-9.)... 

Anemia in hemodialysis (10) and mainly in renal transplant patients has been reported (11-13). The suggested mechanism is by an action on erythropoietin, similar to that of ACE inhibitors, which produce the same adverse effect. However, in a small uncontrolled but prospective study, losartan given for 3 months to 15 patients on chronic hemodialysis with anemia, neither altered plasma erythropoietin concentrations nor aggravated the anemia (14). In those taking losartan there was no need for higher doses of co-administered r-Hu Epo in order to correct anemia, in contrast to controls. 

Anemia is observed in some CF patients despite chronic hypoxia. The apparent deficient erythroid response occurs, at least in part, from disturbances in erythropoietin regulation and iron availabihty (impaired gastrointestinal absorption). Despite chronic hypoxia in some patients with CF, erythropoietin concentrations are normal or low. The condition is characterized by decreased hematocrit and serum ferritin, increased carboxyhemoglobin, and normal or low hemoglobin. Vitamin E concentrations may be normal. Many patients may have iron deficiency owing to decreased dietary intake, malabsorption, or blood loss. 

These range-finding results and data from the literature can be used to provide the initial target assay range. For example, erythropoietin concentrations in nonsmokers, smokers, and cancer patients are shown in Table 6.2. The concentrations, 9.2, 15.2, and 21.9mU/mL for nonsmokers (A =25), smokers (N = 14), and cancer patients (N= 10), respectively, illustrate the need for establishing normal ranges in a target population. 

A mathematical model of the control system for erythropoiesis is presented. It is postulated that the rate of erythropoiesis is controlled by a hormone, erythropoietin, which is released from the kidney in response to reduced renal oxygen supply. Equations are developed relating erythropoietin release to arterial oxyhemoglobin concentration, and hemoglobin production to plasma erythropoietin concentration, with appropriate time delays. Effects of plasma volume changes during hypoxia are included. The model simulates the dynamic response of the erythropoietic system to a step decrease in the pOt of inspired air. Contributions of the parameters and relationships to the predicted response are analyzed. The model response compares favorably with experimental data obtained from mice subjected to different degrees of hypoxia. 

Figure 1. Block diagram of a model for the control of erythropoiesis (HbO), oxyhemoglobin concentration Vi, viscosity factor (HbO), effective oxyhemoglobin concentration R, rate of erythropoietin release (E), plasma erythropoietin concentration E0, normal plasma erythropoietin concentration V , distribution volume for erythropoietin P, rate of hemoglobin production MT, erythrocyte maturation time L, rate of hemoglobin loss TH, total circulating hemoglobin (Hb), blood hemoglobin concentration Vb, blood volume Vp, plasma volume Vp0, normal plasma volume Vpf, steady-state hypoxic plasma volume MCV, mean corpuscular volume MCH, mean corpuscular hemoglobin k, constant...

A delay of 4 hours (Ti) was incorporated into the model between changes in oxyhemoglobin concentration and subsequent erythropoietin release to account for the time required from release of the renal erythropoietic factor to the development of active erythroproietin in the blood stream (3). Values for Ki and K2 were estimated for the mouse by scaling a relationship derived from data in rats, relating oxyhemoglobin concentration to erythropoietin release (I). It was assumed that the released erythroproietin mixes instantly in a volume equal to twice the plasma volume and that the disappearance rate of erythropoietin is proportional to the plasma erythropoietin concentration with a disappearance constant of. 130 day (4). 

In the model, plasma erythropoietin concentration was used to determine the amount of hemoglobin produced and the time delay before new red blood cells (hemoglobin) are released into the blood stream. Equation 2 shows the postulated relationship between the rate of hemoglobin production and plasma erythropoietin concentration. 

P(t) = rate of hemoglobin production at time t Pm = maximum rate of hemoglobin production [E( t)] = plasma erythropoietin concentration at time t K3 and K4 are constants... 

The maximum rate of hemoglobin production is assumed to be seven times the normal production. The two constants, K3 and K4, were calculated using the conditions that (1) normal erythropoietin concentration results in normal hemoglobin production and (2) a basal hemoglobin production of. 005 gram/day occurs when erythropoietin concentration is zero. 

Two relationships were used to determine the time delay (maturation time) between the stimulation of red blood cell production by erythropoietin and the release of mature red blood cells (hemoglobin) into the blood stream. Normally cells are assumed to mature and enter the blood stream 3.75 days after stimulation by erythropoietin. However, this maturation time can vary from 2.5 to approximately 4.0 days, depending on the plasma erythropoietin concentration at the time of stimulation. This relationship is shown in Equation 3. 

E is the arbitrarily selected value of erythropoietin concentration above which the maturation time will remain at 2.5 days. was calculated by assuming 3.75 days maturation time for normal erythropoietin concentration. 

With very high concentrations of erythropoietin, a few of the cells skip one of the mitotic divisions during maturation and are released prematurely into the blood stream. In the model these early cells mature and enter the blood stream 1.5 days after stimulation by erythropoietin. Early cells are produced only when erythropoietin concentration is greater than a preselected value (Ee). The percentage of hemoglobin released in early cells is calculated as shown in Equation 4. 

Ee) = erythropoietin concentration below which no early cells are produced... 

In response to sustained hypoxia, the model predicts a sudden increase in plasma erythropoietin concentration followed by a rapid decrease with the maximum at approximately 12 hours. This type of response has been reported for man and animals (9, 10, II, 12). However, in contrast to the reported experimental data, the erythropoietin levels predicted by the original model did not return to baseline levels after a few days of hypoxia. It appears that some mechanism not included in the model allows a continuing high level of erythropoiesis even after the plasma erythropoietin concentration has returned to near baseline levels. Such a mechanism has been proposed by Kretchmar in a model for the action of erythropoietin (13). His model predicts that the sensitivity of erythropoietin depends on the preceding level of stem cell differentiation. Increased erythropoietin concentration causes an immediate increase in stem cell differentiation as well as an increase in the effectiveness of erythropoietin during a subsequent period. His model also predicts a temporary reduction in the effectiveness of erythropoietin between an initial increase in erythropoietin concentration and the subsequent increase in erythropoietin effectiveness. 

With the relationship between oxyhemoglobin concentration and erythropoietin production selected to provide good agreement of erythropoietin concentration changes and experimental data, the constants in Equation 2 (hemoglobin production) were modified to produce a better total hemoglobin response. The conditions were that (1) normal plasma... 

Figure 8. Model predictions for plasma erythropoietin concentration as a function of duration of hypoxic exposure at 360 mm Hg total pressure. The model responses were obtained with the parameter values listed in Table 1. The solid line was generated with the changes in plasma volume and arterial p0 as described in the text and included in the model. The broken lines were obtained with either the plasma volume held constant or arterial p02 held at the acute level for the duration of hypoxic exposure.

Hopeee SM, Sundeeman FW JR and Goldwasser E (1985a) Effects of unilateral intrarenal administration of nickel subsulfide to rats on erythropoietin concentrations in serum and in extracts of both kidneys. In Brown SS, Sunderman FW Jr, eds. Progress in Nickel Toxicology, pp. 97-100. Blackwell, Oxford. 

Pratt MC, Lewis-Bamed NJ, Walker RJ, Bailey RR, Shand BI, Livesey J. Effect of angiotensin converting enz5nne irihibitors on erythropoietin concentrations in healthy volunteers. BrJ Clin Pharmacol (1992) 34, 363-5. 

Ranges fcr the current EP standard, thEPO BRP batch 2 have been modified (see Behr-Gross, M.-E., Daas, A. and Bristow, A., Pharmemopa Bio, 2004, 1, 23, 2004). Source Erythropoietin concentrated solution,... 

Erythropoietin concentrated solution 01/2005 1316, European Pharmacopoeia 5th edition, published by EDQM. June 2004. 

Liebelt, Ei., Schonfeld, DJ., Gallagher, P., 1999. Elevated blood lead levels in children are associated with lower erythropoietin concentrations. J. Pediatr. 134, 107—109. 

Batch potency testing of erythropoietin concentrated solution In vivo... 

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