ACE inhibitors do not induce recombinant human erythropoietin resistance in hemodialysis patients

Anemia of Chronic Kidney Disease-A Narrative Review of Its Pathophysiology, Diagnosis, and Management

Anemia is one of the most common chronic kidney disease (CKD) complications. It negatively affects patients' quality of life and clinical outcomes. The pathophysiology of anemia in CKD involves the interplay of various factors such as erythropoietin (EPO) deficiency, iron dysregulation, chronic inflammation, bone marrow dysfunction, and nutritional deficiencies. Despite recent advances in understanding this condition, anemia still remains a serious clinical challenge in population of patients with CKD. Several guidelines have been published with the aim to systematize the diagnostic approach and treatment of anemia; however, due to emerging data, many recommendations vary between publications. Recent studies indicate a potential of novel biomarkers to evaluate anemia and related conditions such as iron deficiency, which is often present in CKD patients. Our article aims to summarize the pathophysiology of anemia in CKD, as well as the diagnosis and management of this condition, including novel therapeutic approaches such as hypoxia-inducible factor-prolyl hydroxylase inhibitors (HIF-PHI). Understanding these complex subjects is crucial for a targeted approach to diagnose and treat patients with anemia in CKD effectively.

Low-Dose Erythropoietin Amplifies Beneficial Effects of Angiotensin II Blockade on Glomerulosclerosis

Exogenous erythropoietin (EPO) is used to treat anemia in patients with chronic kidney disease (CKD). Concerns about the possible adverse effect of EPO on the progression of CKD have been raised owing to nonerythroid cell effects. We investigated the effects of low-dose EPO, independent of correcting anemia, on existing glomerulosclerosis. Adult mice underwent 5/6 nephrectomy and were randomized into the following 4 groups at week 8 after surgery: vehicle (VEH), losartan (angiotensin II type 1 receptor blocker [ARB]), darbepoetin-α (DA), or combination (DA+ARB). Four weeks later, mice were euthanized, followed by evaluation of renal structure and function. Glomerular endothelial cells and podocytes were cultured to evaluate the effects of DA on cell migration, apoptosis, and Akt signaling. ARB reduced blood pressure, albuminuria, and the level of serum creatinine and increased hematocrit compared with VEH, whereas low-dose DA only reduced the level of serum creatinine. Combination treatment showed a trend to increase hematocrit and survival compared with ARB alone. Combination treatment but not ARB alone significantly reduced the progression of glomerulosclerosis compared with VEH. Low-dose DA resulted in more preserved glomerular and peritubular capillary endothelial cells with increased p-Akt and even further endothelial cell preservation in combination with ARB. In cultured glomerular endothelial cells, angiotensin II induced more apoptosis, reduced migration, and decreased p-Flk1, a receptor for the proangiogenic vascular endothelial growth factor. DA counteracted these injuries and increased p-Akt, a key factor in angiogenesis and cell survival. DA also protected cultured podocytes against transforming growth factor β-induced apoptosis and synaptopodin loss. Low-dose EPO directly protects glomerular and peritubular endothelial cells via Akt phosphorylation. Therefore, treatment using a combination of low-dose EPO and ARB results in less progression of glomerulosclerosis in an experimental CKD model.

Erythropoietin Resistance Index and the Affecting Factors in Children with Peritoneal Dialysis

BACKGROUND

Erythropoiesis-stimulating agents (ESAs) are used to treat anemia in CKD. Erythropoietin resistance index (ERI) is a useful tool used to evaluate the response to ESAs. In this study, we aimed to evaluate the causes of high ERI in children undergoing peritoneal dialysis (PD).

METHOD

Patients who had been on PD for at least 1 year were included in this retrospective study. Demographic characteristics, residual kidney function (RKF), adequacy of dialysis, peritoneal glucose exposure, the number and reason for hospitalization, and medications were recorded. Anemia and laboratory parameters that may affect anemia were noted by taking the average of laboratory values in the last follow-up year (time-averaged). The weekly ESA dose was proportioned to the annual average hemoglobin value and body weight to calculate the ERI in terms of U/kg/week/g/dL.

RESULTS

A total of 100 patients were included in the study. The mean ESA dose and ERI value were 119.8 ± 66.22 U/kg/week and 13.01 ± 7.52 U/kg/week/g/dL, respectively. It was determined that the patients <5 years of age have very high ERI value, and these patients need 2 times more ESA than those >10 years of age. Absence of RKF, large number of hospitalization, and ACEI use were also found to affect the ERI value negatively.

CONCLUSION

We demonstrate that the most important factor affecting ERI value is young age. We also reveal that absence of RKF, large number of hospitalization, and ACEI use are also important variables affecting the ERI value.

Angiotensin-Converting Enzyme Gene Polymorphism and Erythropoietin Requirement

Objectives

To study the effect of angiotensin-converting enzyme (ACE) polymorphisms II, ID, and DD on erythropoietin (EPO) requirement in patients on continuous ambulatory peritoneal dialysis (CAPD) therapy.

Design

Retrospective observational study.

Setting

CAPD Unit, Royal London/St. Bartholomews Hospital, London, UK.

Patients

46 patients on the transplant waiting list (age 20 – 70 years), on CAPD therapy for an average of 28 months, seen consecutively over a period of 3 months in the outpatients department.

Main Outcome Measures

Primary end point: EPO dose requirement in different ACE genotypes. Secondary end points: C-reactive protein, ferritin, parathyroid hormone, Kt/V, duration of dialysis, folate, cause of renal failure, and whether or not patients were on ACE inhibitor therapy.

Results

There was a statistically significant difference ( p < 0.05) in EPO requirement in the II/ID group compared to the DD group. The mean ± standard error of EPO for the II/ID group was 144 ± 15 U/kg/week, and for the DD group, 87 ± 9 U/kg/ week. The difference in EPO requirement could not be explained by age, C-reactive protein, ferritin, parathyroid hormone, Kt/V, duration of dialysis, folate, cause of renal failure, or whether or not patients were on ACE inhibitor therapy.

Conclusion

In CAPD patients, ACE genotype has predictive value when determining the EPO dosage, as the II/ID genotype may be associated with a suboptimal response.

Effect of angiotensin-converting enzyme gene insertion/deletion polymorphism and angiotensin-converting enzyme inhibition on erythropoiesis in patients on haemodialysis

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACEis) improve survival; however, their effect on erythropoiesis remains a matter of debate in this population. Since insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene largely influences serum ACE activity, its effect on erythropoiesis is also anticipated.

METHOD

In this multicentre, cross-sectional study of 660 patients on maintenance haemodialysis, we analysed the effect of ACEi use and ACE gene I/D polymorphism on haemoglobin levels and erythropoietin resistance. Patients were allocated in groups based on genotype and ACEi therapy. We identified 128 matched pairs with I/I and D/D genotypes.

RESULT

There was no difference in haemoglobin levels between genotype groups. Haemoglobin levels were lower in patients on ACEi therapy in the entire cohort (95.5±12.1 g/l vs 97.4±13.4 g/l, p=0.02) and patients with I/D (95.2±11 g/l vs 98.2±11.9 g/l, p=0.04) and D/D (93.3±13.2 g/l vs 97.4±14.2 g/l, p=0.02) genotypes. In patient pairs treated with ACEi therapy, subjects with D/D genotype had lower Haemoglobin level (93.0±12.8 g/l vs 98.2±11.9 g/l, p=0.006) and higher erythropoietin resistance index (ERI) (199.1 vs 175.0, p=0.046) than individuals with I/I genotype.

CONCLUSION

These results indicate that ACEi therapy may increase erythropoietin resistance and worsen erythropoiesis in haemodialysis patients with the D allele.

Do diabetic dialysis patients require more or less of erythropoietin?

BACKGROUND AND OBJECTIVES

To evaluate differences in erythropoietin requirements between diabetic and non-diabetic patients on hemodialysis and peritoneal dialysis.

DESIGN AND SETTINGS

This was a retrospective, cross-sectional study conducted between January 2010 and December 2011, at King Khalid University Hospital Riyadh, Saudi Arabia, with 47 peritoneal and 57 hemodialysis patients.

METHODS

A total of 24 (51%) peritoneal dialysis and 30 (52.6%) hemodialysis patients were suffering from diabetes. We compared demographics, hemoglobin, ferritin, transferrin saturation, C-reactive protein, parathyroid hormone, and weekly erythropoietin dose.

RESULTS

The mean weekly dose of erythropoietin was 5391.3 (4692.7) units in peritoneal dialysis (diabetic and non-diabetic) patients compared to 9869.7 (5631.7) units in hemodialysis (diabetic and non-diabetic) patients, with a difference of 4478.3 (6615) units (P=.001). The mean weekly dose in diabetic peritoneal dialysis patients was 3818.2 (4489.5) units, compared to 8814.8 (5121.9) units in hemodialysis (P=.001) patients. The mean weekly dose in non-diabetic peritoneal dialysis patients was 6545.4 (3863.5) units compared to 12 222 (6210) units in non-diabetic hemodialysis patients (P=.02). Diabetic peritoneal dialysis patients required a lower dose of erythropoietin compared to non-diabetic peritoneal dialysis patients (3818.2 [4489.5] units vs 6545.4 [3863.5] units per week) (P=.036). In hemodialysis patients, the mean erythropoietin dose was lower in diabetic patients compared to non-diabetic patients (8814.8 [5121.9] units vs 12 222 [6210] units per week) (P=.043).

CONCLUSION

The diabetic patients in both groups (hemodialysis and peritoneal dialysis) required less erythropoietin than non-diabetic patients. Diabetic patients on peritoneal dialysis required less erythropoietin diabetic patients on hemodialysis.

Lisinopril pharmacokinetics and erythropoietin requirement in haemodialysis patients

BACKGROUND

There is ongoing controversy whether angiotensin-converting enzyme inhibitors (ACE-I) contribute to anaemia by causing hyporesponsiveness to erythropoiesis-stimulating agents (ESA). However, it is unknown whether or not plasma levels or area under the curve (AUC) of ACE-I are associated with responsiveness to ESA therapy.

MATERIALS AND METHODS

We examined the association between lisinopril AUC, lisinopril plasma levels and ESA requirements that was assessed using an ESA index [(ESA IU/week/body weight kg)/(haemoglobin g/dL)]. After screening 184 haemodialysis patients, 14 fulfilled the inclusion criteria, mainly long-term use of oral lisinopril in the upper end of dosage range for this population with stable haemoglobin levels and intravenous ESA therapy. Lisinopril plasma levels were measured at eight different time points (predialysis, immediate post-dialysis and hourly for 6h thereafter; AUC1), and the seven post-dialysis lisinopril plasma levels were used for calculation of AUC2.

RESULTS

The mean ESA index of all patients was 27·90±25·84 (IU/week/kg)/(g/dL). Average lisinopril AUC1 was 1212·48±1209·75 [mg*h/L], whereas AUC2 averaged 947·67±977·07 [mg*h/L]. Two patients (14%) had no detectable lisinopril plasma levels, indicating their noncompliance. There was no association between ESA index and AUC or plasma levels of lisinopril at any time point for all 14 or for the 12 compliant patients.

CONCLUSIONS

Our study shows that long-term, high-dose lisinopril therapy has no effect on ESA responsiveness. Thus, avoidance or a dose reduction of ACE-I in dialysis patients will not necessarily lead to reduced ESA requirements and costs.

Role of residual renal function in phosphate control and anemia management in chronic hemodialysis patients

BACKGROUND AND OBJECTIVES

There is increasing awareness that residual renal function (RRF) has beneficial effects in hemodialysis (HD) patients. The aim of this study was to investigate the role of RRF, expressed as GFR, in phosphate and anemia management in chronic HD patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline data of 552 consecutive patients from the Convective Transport Study (CONTRAST) were analyzed. Patients with a urinary output≥100 ml/24 h (n=295) were categorized in tertiles on the basis of degree of GFR and compared with anuric patients (i.e., urinary output<100 ml/24 h, n=274). Relations between GFR and serum phosphate and erythropoiesis-stimulating agent (ESA) index (weekly ESA dose per kg body weight divided by hematocrit) were analyzed with multivariable regression models.

RESULTS

Phosphate levels were between 3.5 and 5.5 mg/dl in 68% of patients in the upper tertile (GFR>4.13 ml/min per 1.73 m2), as compared with 46% in anuric patients despite lower prescription of phosphate-binding agents. Mean hemoglobin levels were 11.9±1.2 g/dl with no differences between the GFR categories. The ESA index was 31% lower in patients in the upper tertile as compared with anuric patients. After adjustments for patient characteristics, patients in the upper tertile had significantly lower serum phosphate levels and ESA index as compared with anuric patients.

CONCLUSIONS

This study suggests a strong relation between RRF and improved phosphate and anemia control in HD patients. Efforts to preserve RRF in HD patients could improve outcomes and should be encouraged.

Association between erythropoietin requirements and antihypertensive agents

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACI) and angiotensin II receptor blockers (ARB) have been reported to increase recombinant human erythropoietin (rHuEPO) requirements. We performed a cross-sectional study to investigate an association of antihypertensive agents including these two with the rHuEPO dose in chronic hemodialysis patients.

METHODS

We studied 625 patients undergoing hemodialysis therapy in 11 dialysis units. The association between the rHuEPO dose and antihypertensive agents was statistically analyzed.

RESULTS

The mean hemoglobin (Hb) level and rHuEPO dose corrected by body weight were 10.5 g/dl and 95.2 U/kg/week, respectively. When the patients were subdivided into four groups according to the number of prescribed antihypertensive agents (G-0, G-1, G-2, and G-3; patients prescribed with no medication, 1, 2, and >3 drugs, respectively), a significantly low dose of rHuEPO was observed in G-0 compared to the other groups. Unpaired t test showed a higher dose of rHuEPO in the presence of ARB, alpha-blockers, or calcium channel blockers (CCB). The rHuEPO dose was higher in the elderly, in females, and in patients with diabetes or hypertension. In multiple regression analysis, age, sex, rHuEPO dose, serum albumin level, and duration of dialysis therapy but not antihypertensive drugs were independent factors for the Hb level. In contrast, the rHuEPO dose was significantly associated with a low level of Hb, age, females, and CCB use. However, since CCB use was strongly associated not only with rHuEPO dose but also with systolic blood pressure and the use of alpha-blockers and ARB, these findings might be caused by erythropoietin (EPO)-induced hypertension.

CONCLUSION

There was an association between the number of antihypertensive agents and rHuEPO dose in chronic hemodialysis patients. However, no significant relation was indicated between ARB/ACI use and EPO requirements.

Multiorgan-protective actions of blockers of the renin-angiotensin system, statins and erythropoietin: common pleiotropic effects in reno-, cardio- and neuroprotection

Renal diseases induce nephroprotective measures that may affect the heart, brain and other organs. In addition, many cardiovascular and neurological diseases are accompanied by renal lesions. For these reasons, multiorgan-protective measures, including cardio-, reno- and neuro-protective measures, are necessary to treat these diseases. The drugs used in nephrology are often pleiotropic. Although they usually address a single organ or tissue, many of them have complex actions that may provide multiorgan-protection. The present paper aims to review 3 classes of drugs that are commonly prescribed in nephrological practice: statins, RAS blockers (such as ACEIs and ARBs) and erythropoietin (EPO). This paper highlights the renoprotective actions, as well as those that are protective of the heart, brain and other organs, of these drugs at the cellular and molecular level. Their protective actions are attributable to their main effects and pleiotropic effects. The protective pleiotropic actions of these drugs may be exerted on multiple organs, making them multiorgan-protective. Another objective is to analyse the shared multiorgan-protective pleiotropic effects of RAS blockers (ACEIs and ARBs), statins and erythropoietin. This will allow for the practical association of the main renoprotective drugs with multiorgan protection.

Prevalence and Prognostic Significance of Anemia in Patients With Congestive Heart Failure Treated With Standard vs High Doses of Enalapril

BACKGROUND

Anemia is common in patients with congestive heart failure (CHF), although its etiology and pathophysiology remain largely unexplained. The purpose of this study was to examine the prognostic significance of a low hematocrit (Hct) in patients with CHF and the possible role of angiotensin-converting enzyme inhibition in anemia development.

METHODS

Hct was measured at the time of enrollment of 160 patients with CHF, mean age 56 +/- 12 years, in New York Heart Association (NYHA) functional class 2.6 +/- 0.7 and with left ventricular ejection fraction of 20 +/- 9%. They were randomized to standard (mean: 17.9 +/- 4.3 mg/day) or high (mean: 42 +/- 19.3 mg/day) doses of enalapril. The follow-up duration was 2 years. Cox regression models were used to identify prognostic factors, and correlations among individual variables were tested.

RESULTS

Mean baseline Hct was 42.7 +/- 5%. In multivariate analyses, low Hct (p = 0.036), older age (p = 0.022) and low systolic blood pressure (p = 0.032) were independent predictors of death within 2 years. A correlation was found between baseline Hct and NYHA class (Spearman's correlation coefficient: -0.183, p = 0.008). A significant decrease in Hct from 43.2 +/- 4.9% at baseline to 40.7 +/- 4.4% at 2 years was observed in the group treated with high doses of enalapril (p < 0.001).

CONCLUSIONS

Low baseline Hct predicted poor 2-year prognosis in patients with CHF. Enalapril administered in high doses increased the incidence of anemia in this population. The underlying pathophysiologic mechanism and effects of maintaining a normal Hct on clinical outcomes remain to be determined.

Effect of valsartan on erythropoietin and hemoglobin levels in stage III-IV chronic kidney disease patients

Angiotensin-converting enzyme inhibitors (ACEIs) were accepted as a potential cause of inadequate epoetin response in chronic kidney disease (CKD) patients. We aimed to determine the effects of valsartan, an angiotensin receptor blocker (ARB), on serum ertyhropoietin levels and on certain biochemical and haematological parameters in hypertensive CKD patients. Twenty-two stage III-IV CKD patients (mean age; 56.8 +/- 8.9 years, 12 male 10 female) were included in the study. Before initiating the treatment, current anti-hypertensive treatments (if any) were discontinued, and blood samples were collected after a washout period of 3 weeks. Valsartan 80 mg/day was started, and additional anti-hypertensive agents were given according to study protocol if needed. One way Anova and paired t-tests were used for statistical comparisons. Serum blood urea nitrogen (BUN), creatinine, uric acid, potassium, haemoglobin and erythropoietin values were measured, and glomerular filtration rates were calculated before and 3, 6 and 90 days after valsartan treatment, a significant reduction in EPO level was observed at 3rd (19.6 +/- 24.0 vs. 13.8 +/- 8.5, p = 0.010), 6th (12.1 +/- 7.6, p = 0.009), and 90th days (8.3 +/- 5.4, p = 0.007). When pre-treatment values were compared with 90th day results, no significant change was observed in terms of hgb, htc, serum BUN, creatinine, uric acid, potassium, and GFR values. In conclusion, valsartan, an ARB, did not decrease haemoglobin levels in stage III-IV CKD patients despite significant reduction in serum erythropoietinlevels, so ARBs may be preferred to ACEIs in CKD patients when indicated.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

Drug therapy for hypertension in hemodialysis patients

The majority of end-stage renal disease (ESRD) patients are hypertensive. Drug therapy for hypertension in hemodialysis (HD) patients includes all classes of antihypertensive drugs, with the sole exception of diuretics. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers may decrease morbidity and mortality by reducing the mean arterial pressure (MAP), aortic pulse wave velocity, and aortic systolic pressure augmentation, as well as left ventricular hypertrophy (LVH) and probably reduction of C-reactive protein (CRP) and oxidant stress. Potential risk factors include hyperkalemia, anaphylactoid reaction with AN69 membranes (particularly ACE inhibitors), and aggravation of renal anemia. beta-blockers decrease not only mortality, blood pressure (BP), and ventricular arrhythmias, but also improve left ventricular function in ESRD patients. Nonselective beta-blockers can cause an increase in serum potassium (particularly during fasting or exercise). Lisinopril and atenolol have a predominant renal excretion and therefore a prolonged half life in ESRD patients. Thus thrice-weekly supervised administration of these drugs after HD can enhance BP control. The use of calcium channel blockers is also associated with lower total and cardiovascular-specific mortality in HD patients. Minoxidil is a very potent vasodilator that is generally reserved for dialysis patients with severe hypertension. Hypertensive dialysis patients who are noncompliant with their medications may benefit from transdermal clonidine therapy once a week. The majority of dialysis patients need a combination of several antihypertensive drugs for adequate BP control.

Treating anemia early in renal failure patients slows the decline of renal function: a randomized controlled trial

BACKGROUND

Erythropoietin is known to improve outcomes in patients with anemia from chronic renal disease. However, there is uncertainty about the optimal timing of initiation of erythropoietin treatment in predialysis patients with non-severe anemia.

METHODS

We conducted a randomized controlled trial of early versus deferred initiation of erythropoietin in nondiabetic predialysis patients with serum creatinine 2 to 6 mg/dL and hemoglobin 9 to 11.6 g/dL. The early treatment arm was immediately started on 50 U/kg/wk of erythropoietin alpha with appropriate titration aiming for hemoglobin of > or =13 g/dL. The deferred treatment arm would start erythropoietin only when hemoglobin decreased to <9 g/dL. The primary end point was a composite of doubling of creatinine, renal replacement, or death.

RESULTS

Eighty-eight patients were randomized (early treatment N= 45, deferred treatment N= 43) and followed for a median of 22.5 months. During follow-up, 13 versus 23 patients reached the primary end point in the two arms, respectively (log-rank P= 0.0078). The relative hazard for reaching an end point was 0.42 (P= 0.012). Adjusting for baseline serum creatinine, the adjusted relative hazard was 0.37 (P= 0.004), while the risk increased 2.23-fold (P < 0.001) per 1 mg/dL higher creatinine at baseline. The benefit was similar regardless of the baseline hemoglobin and proteinuria. No patients had any severe adverse events.

CONCLUSION

Early initiation of erythropoietin in predialysis patients with non-severe anemia significantly slows the progression of renal disease and delays the initiation of renal replacement therapy.

Cardiovascular risk in stage 4 and 5 nephropathy

Severity of heart disease of almost all types, as well as mortality risk associated with heart disease, increases in step with severity of kidney disease, although not necessarily in a linear fashion. Heart failure is more common and just as lethal as ischemic heart disease in patients with severe chronic kidney disease (CKD). The incidence of nonfatal heart disease in dialysis and transplant populations has now been described in detail. Although standard risk factors for heart disease that are more common among patients with CKD than in the general population do not adequately explain the greatly increased risk of heart disease in patients with severe CKD, neither do as yet identified "nontraditional" risk factors. However, in addition to the factors not common in the general population, such as anemia, hyperphosphatemia, and markers of systemic inflammation, patients with CKD in the modern era may also exhibit excessive thrombotic tendencies. Screening for heart disease in this population relies mainly on dobutamine stress echocardiography or nuclear scintigraphy. The role of electron beam CT (EBCT) scanning is currently controversial. The indications for coronary angiography are the same for patients with CKD as for the general population, but patients with CKD are at greatly increased risk for contrast-associated nephropathy, the least controversial preventive therapy, which consists of isotonic saline and N-acetylcysteine. Finally, patients with CKD do not currently receive adequate medical therapy for prevention and treatment of heart disease.

Congestive heart failure in patients with chronic kidney disease and on dialysis

CHF is highly prevalent in ESRD and is a leading cause of death in such patients. Hypertension, renal anemia, and comorbid conditions such as coronary artery disease are particularly important risk factors for CHF in ESRD. Dialysis hypotension may be a marker of poor prognosis in such persons. Recent studies suggest that lipid peroxidation and L-carnitine deficiency may contribute to CHF in some patients with ESRD. All forms of renal replacement therapy are capable of ameliorating symptoms of CHF, but their effect on cardiovascular mortality has not been firmly established. Drug therapy, particularly angiotensin-converting enzyme inhibitors and beta-adrenergic receptor blockers, is under-used in patients with ESRD and CHF. Heart/kidney transplantation may be a viable option for some patients with advanced CHF and ESRD.

Why is erythropoietin made in the kidney? The kidney functions as a 'critmeter' to regulate the hematocrit

The normal hematocrit is not a random number, but one that maximizes oxygen delivery. While the feedback loop wherein tissue oxygen pressure determines the production of erythropoietin, which further drives the production of red blood cells in the bone marrow, explains how the hematocrit is generated, it does not speak to how the hematocrit is regulated. The regulation of the hematocrit requires the coordination of the plasma volume and the red cell mass. By controlling red cell mass via erythropoietin and plasma volume through excretion of salt and water, the kidney is able to generate the hematocrit. It is hypothesized that the kidney functions as a critmeter by sensing the relative volumes of each component of the blood through the common signal of tissue oxygen tension. The kidney's unique ability to sense ECF volume through tissue oxygen signal allows it to coordinate these two volumes to produce the normal hematocrit. Hence, it may be the kidneys ability to report a measure of ECF volume as a tissue oxygen signal and thus to regulate the hematocrit that establishes it as the logical site of erythropoietin production. The critmeter is proposed to be a functional unit located at the tip of the cortical labyrinth at the juxta-medullary region of the kidney where erythropoietin is made physiologically. Renal vasculature and nephron segment heterogeneity in sodium reabsorption likely provides the anatomical construct to generate the marginal tissue oxygen pressure required to trigger the production of erythropoietin. The balance of oxygen consumption for sodium reabsorption and oxygen delivery is reflected by the tissue oxygen pressure. This balance hence determines RBC mass adjusted to plasma volume. Factors that affect blood supply and sodium reabsorption in a discordant manner may modulate the critmeter, e.g. angiotensin II. The objective of this work is to describe the hypothesis of the kidney's function as a critmeter, including the anatomical and physiological components, and the role of the renin-angiotensin system in modulating erythropoietin. Clinical examples of the dysregulation of the critmeter may be found in the anemia of renal failure and in sports anemia.

Advances in Anemia Management in Chronic Kidney Disease

The prevalence of chronic kidney disease (CKD) is increasing in the United States. Efforts to promote earlier intervention to screen for CKD and manage secondary complications are of paramount importance to improve overall care of this population. Anemia is a secondary complication of CKD that develops as kidney function declines. Historically, anemia management efforts have been primarily emphasized in patients with end-stage renal disease; however, early detection and treatment of anemia in the early stages of the disease are essential to prevent negative consequences of anemia such as reduced quality of life, left ventricular hypertrophy and mortality. With the increased prevalence of CKD and efforts focused on identifying this disorder early in its course, it is likely that more pharmacists will be involved in the management of CKD and secondary complications such as anemia. Treatment approaches must also be based on the more recently advocated guidelines from the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI). This article reviews therapeutic issues of anemia of CKD, new agents for management, and the NKF-K/DOQI anemia management guidelines from a clinical perspective that will assist pharmacists involved in the care of these patients.

Mortality benefit of angiotensin-converting enzyme inhibitors after cardiac events in patients with end-stage renal disease

HYPOTHESIS/INTRODUCTION: The risks and benefits of angiotensin-converting enzyme (ACE) inhibitors in patients with end-stage renal disease (ESRD) after cardiac events are unknown. We sought to determine the independent effect of ACE inhibitors (ACE-I) on long-term mortality in ESRD patients after cardiac events.

MATERIALS AND METHODS

We analysed a prospective coronary care unit registry and identified 527 ESRD patients, 368 with complete data on medications prescribed, over eight years at a single, tertiary centre.

RESULTS

The overall mean age was 64.4+13.8 years with 54.9% men, and 59.2% African-American. A total of 143/386 (37.0%) were prescribed ACE-I during the hospital stay for cardiac reasons, including congestive heart failure (CHF) 52.8% and acute coronary syndromes (ACS) 47.2%. There were no significant differences in the rates of hypotension or arrhythmias in those who were treated with ACE-I versus those who were not. Survival analysis over three years, adjusted for known confounders, demonstrated a 37% reduction in all-cause mortality in those who received ACE-I, (p=0.0145).

CONCLUSIONS

In the setting of coronary care unit admission for CHF and ACS, ESRD patients selected for ACE-I, did not have increased rates of adverse haemodynamic or arrhythmic complications. The use of ACE-I conferred an independent mortality reduction over long-term follow-up.

Darbepoetin alfa: a novel erythropoiesis-stimulating protein

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical efficacy, and safety of darbepoetin alfa.

DATA SOURCES

Pertinent references were identified by a MEDLINE search (1995-January 2001) of the medical literature, review of English-language literature and references of these articles, product information, and abstracts from professional meetings.

STUDY SELECTION

Clinical efficacy data were gathered from all available trial data citing darbepoetin alfa. Additional information concerning pharmacology, pharmacokinetics, and safety was also reviewed.

DATA SYNTHESIS

Darbepoetin alfa is a new erythropoiesis-stimulating protein with a threefold longer half-life than recombinant human erythropoietin (r-HuEPO). Darbepoetin alfa is approved for intravenous and subcutaneous administration in patients requiring and not requiring dialysis. Clinical studies in patients with chronic kidney disease (CKD) have shown darbepoetin alfa to be equivalent to r-HuEPO in terms of increases in hemoglobin concentration, percentage of patients obtaining target hemoglobin, and average time to reach target hemoglobin concentration. Trials are currently ongoing in patients receiving cancer chemotherapy. The adverse event profile appears to be similar between the 2 agents.

CONCLUSIONS

The equivalent efficacy and safety profile, as well as the longer half-life, may make darbepoetin alfa an attractive alternative to r-HuEPO in patients with CKD. Since these patients need to receive r-HuEPO 1-3 times weekly at the expense of increased healthcare utilization to improve their hemoglobin, agents such as darbepoetin alfa, with longer durations of action, may reduce healthcare expenses. In addition, enhanced patient compliance may be realized with once-weekly or once every-other-week administration.

Effects of angiotensin-converting enzyme inhibitors on the treatment of anemia with erythropoietin

BACKGROUND

The hypothesis that angiotensin-converting enzyme (ACE) inhibitors interfere with the treatment of anemia with recombinant human erythropoietin (rHuEPO) remains controversial. To test this hypothesis, a retrospective analysis was conducted in a large group of hemodialysis patients with renal anemia.

METHODS

The effects of ACE inhibitors in these patients were evaluated by measuring the weekly increment in hematocrit (DeltaHct) values within 12 weeks of the initiation of rHuEPO treatment. Results from 2213 rHuEPO naïve patients were compared between patients receiving rHuEPO alone and patients receiving both rHuEPO and ACE inhibitors. Because of the demographic differences between the two groups, a propensity score was used to eliminate the influence of confounding factors and to match the patient population in these two patient groups. Multiple regression analysis also was performed.

RESULTS

When the DeltaHct values were compared directly between the two groups or were assessed by multiple regression analysis, no effect of ACE inhibitors was observed (P = 0.941 and P = 0.308, respectively). When the effects of ACE inhibitors on the treatment of anemia with rHuEPO were analyzed in 329 patients extracted from each group by their propensity score, DeltaHct did not differ between the two groups (P = 0.355).

CONCLUSIONS

These results suggest that ACE inhibitors have no effect on the rHuEPO treatment for anemia in hemodialysis patients who were treated with a relatively low dose of ACE inhibitors and low-dose rHuEPO.

Plasma levels and metabolism of AcSDKP in patients with chronic renal failure: relationship with erythropoietin requirements

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP) is a physiological inhibitor of hematopoiesis that is maintained at stable levels in normal plasma. Its degradation in vivo and in vitro by angiotensin-converting enzyme (ACE) accounts for the high plasma concentrations of AcSDKP in patients treated with ACE inhibitors. Because ACE inhibitors can induce anemia in some patients, we measured plasma AcSDKP concentrations in 176 patients with chronic renal failure: 120 hemodialysis (HD) and 56 nondialysis (nD) patients, 39 of whom were administered ACE inhibitors. We studied the relationships between AcSDKP levels, hematologic parameters, and recombinant human erythropoietin (rHuEPO) requirements in these patients. AcSDKP levels were significantly greater in HD (10.3 +/- 3.9 pmol/mL) and nD (3.1 +/- 1.8 pmol/mL) patients not administered ACE inhibitors than controls (1.8 +/- 0.2 pmol/mL). In all patients, treatment with ACE inhibitors significantly increased these levels fourfold. HD sessions significantly decreased AcSDKP concentrations by 66% and reduced the predialysis in vitro half-life of AcSDKP (270 +/- 109 minutes) to values (182 +/- 67 minutes) not significantly different from those of controls or nD patients. Most HD patients treated with ACE inhibitors had AcSDKP levels greater than 24 pmol/mL (the greatest concentration found in other nD and HD patients). Only in this group of patients did weekly doses of rHuEPO correlate with AcSDKP levels. Our results show that renal function is essential to maintain stable AcSDKP plasma levels, and at high levels, AcSDKP acts as a uremic toxin causing partial resistance to erythropoietin and inhibiting erythropoiesis.