Iron therapy for renal anemia: how much needed, how much harmful?

Effect of iron supplementation in patients with heart failure and iron deficiency: A systematic review and meta-analysis

Background

The effectiveness of oral and intravenous iron supplementation in reducing the risk of mortality and hospitalizations in HF patients with iron deficiency is not well-established.

Methods

A thorough literature search was conducted across 2 electronic databases (Medline and Cochrane Central) from inception through March 2021. RCTs assessing the impact of iron supplementation on clinical outcomes in iron deficient HF patients were considered for inclusion. Primary end-points included all-cause mortality and HF hospitalization. Evaluations were reported as odds ratios (ORs) or risk ratios (RRs) with 95% confidence intervals (CI) and analysis was performed using a random effects model. I² index was used to assess heterogeneity.

Results

From the 2599 articles retrieved from initial search, 10 potentially relevant studies (n = 2187 patients) were included in the final analysis. Both oral (OR: 0.93; 95% CI: 0.08-11.30; p = 0.951) and intravenous (OR: 0.97; 95% CI: 0.73-1.29; p = 0.840) iron supplementation did not significantly reduce all-cause mortality. However, intravenous iron supplementation significantly decreased the rates of overall (OR: 0.52; 95% CI: 0.33-0.81; p = 0.004) and HF (OR: 0.42; 95% CI: 0.22-0.80; p = 0.009) hospitalizations. In addition, intravenous ferric carboxymaltose therapy significantly reduced the time to first HF hospitalization or cardiovascular mortality (RR = 0.70; 95% CI = 0.50-1.00; p = 0.048), but had no effect on time to first cardiovascular death (RR: 0.94; 95% CI: 0.70-1.25; p = 0.655).

Conclusion

Oral or intravenous iron supplementation did not reduce mortality in iron deficient HF patients. However, intravenous iron supplementation was associated with a significant decrease in overall and HF hospitalizations.

Oxidation of Unsaturated Phospholipids: A Monolayer Study

Lipid oxidation does strongly influence the self-organization of plasma membranes; the detailed influence is not yet clear. In this work, phospholipid monolayers at the air/water interface were used as model membranes. Oxidation was induced by the reactive oxygen species formed in a H₂O₂-enriched solution. The reaction was found to be diffusion-limited; the concentration of the reactive oxygen species was about 50 nM. Isotherms were recorded for different phosphatidylcholines with saturated and unsaturated acyl chains. For unsaturated lipids, the isotherms showed a constant relative molecular area increase after oxidization, independent of the molecular area and dependent on the degree of peroxidation. Similarly, the compressibility modulus was unchanged, but shifted to larger molecular areas. The correlation between peroxidation and changes of the interaction forces between the lipid molecules is discussed.

Cerebro-renal interaction and stroke

Stroke is an event causing a disturbance in cerebral function leading to death and disability worldwide. Both acute kidney injury and chronic kidney disease (CKD) are associated with an increased risk of stroke and cerebrovascular events. The underlying mechanistic approach between impaired renal function and stroke is limitedly explored and has attracted researchers to learn more for developing therapeutic intervention. Common risk factors such as hypertension, hyperphosphatemia, atrial fibrillation, arteriosclerosis, hyperhomocysteinemia, blood-brain barrier disruption, inflammation, etc. are observed in the general population, but are high in renal failure patients. Also, risk factors like bone mineral metabolism, uremic toxins, and anemia, along with the process of dialysis in CKD patients, eventually increases the risk of stroke. Therefore, early detection of risks associated with stroke in CKD is imperative, which may decrease the mortality associated with it. This review highlights mechanisms by which kidney dysfunction can lead to cerebrovascular events and increase the risk of stroke in renal impairment.

Erythropoietic response to oral iron in patients with nondialysis-dependent chronic kidney disease in the FIND-CKD trial

Aims: To evaluate erythropoietic response rates to oral iron over time in iron-deficient anemic patients with nondialysis-dependent chronic kidney disease (ND-CKD). Materials and methods: FIND-CKD was a 1-year, randomized, multicenter trial of iron therapy in patients with ND-CKD, anemia, and iron deficiency, without erythropoiesis-stimulating agent (ESA) therapy. Patients with active infection or C-reactive protein > 20 mg/L were excluded. In this post-hoc analysis, response was defined as ≥ 1 g/dL increase in hemoglobin (Hb) from baseline, before initiation of alternative anemia therapy (i.e., ESA, transfusion, or intravenous iron). Results: 308 patients received oral iron (200 mg elemental iron/day). Mean (SD) Hb at baseline was 10.4 (0.7) g/dL. At week 4, Hb data were available from 292 patients without alternative anemia therapy: 63/292 (21.6%) showed a response. Among the 229 nonresponders at week 4, 48.8% showed a cumulative response on ≥ 1 occasion by week 52 (11.1%, 19.9%, 25.9%, and 28.7% had a response at weeks 8, 12, 24, and 52, respectively), and 27.9% had received alternative iron therapy by week 52. Baseline levels of Hb, ferritin, and transferrin saturation were lower in responders than in nonresponders. Neither concomitant medication nor adherence (as assessed by medication count) was substantially different between early responders and nonresponders. Conclusion: Four weeks after starting oral iron therapy, only 21.6% of anemic patients with ND-CKD and iron deficiency showed an Hb increase of at least 1 g/dL. Among early nonresponders, < 30% responded at any subsequent time point. Earlier consideration of alternative therapy could improve anemia management in this population.

Whole-body iron transport and metabolism: Mechanistic, multi-scale model to improve treatment of anemia in chronic kidney disease

Iron plays vital roles in the human body including enzymatic processes, oxygen-transport via hemoglobin and immune response. Iron metabolism is characterized by ~95% recycling and minor replenishment through diet. Anemia of chronic kidney disease (CKD) is characterized by a lack of synthesis of erythropoietin leading to reduced red blood cell (RBC) formation and aberrant iron recycling. Treatment of CKD anemia aims to normalize RBC count and serum hemoglobin. Clinically, the various fluxes of iron transport and accumulation are not measured so that changes during disease (e.g., CKD) and treatment are unknown. Unwanted iron accumulation in patients is known to lead to adverse effects. Current whole-body models lack the mechanistic details of iron transport related to RBC maturation, transferrin (Tf and TfR) dynamics and assume passive iron efflux from macrophages. Hence, they are not predictive of whole-body iron dynamics and cannot be used to design individualized patient treatment. For prediction, we developed a mechanistic, multi-scale computational model of whole-body iron metabolism incorporating four compartments containing major pools of iron and RBC generation process. The model accounts for multiple forms of iron in vivo, mechanisms involved in iron uptake and release and their regulation. Furthermore, the model is interfaced with drug pharmacokinetics to allow simulation of treatment dynamics. We calibrated our model with experimental and clinical data from peer-reviewed literature to reliably simulate CKD anemia and the effects of current treatment involving combination of epoietin-alpha and iron dextran. This in silico whole-body model of iron metabolism predicts that a year of treatment can potentially lead to 90% downregulation of ferroportin (FPN) levels, 15-fold increase in iron stores with only a 20% increase in iron flux from the reticulo-endothelial system (RES). Model simulations quantified unmeasured iron fluxes, previously unknown effects of treatment on FPN-level and iron stores in the RES. This mechanistic whole-body model can be the basis for future studies that incorporate iron metabolism together with related clinical experiments. Such an approach could pave the way for development of effective personalized treatment of CKD anemia.

Growth and Nutrition in Pediatric Chronic Kidney Disease

Children with chronic kidney disease (CKD) feature significant challenges to the maintenance of adequate nutrition and linear growth. Moreover, the impaired nutritional state contributes directly to poor growth. Therefore, it is necessary to consider nutritional status in the assessment of etiology and treatment of sub-optimal linear growth. The major causes of poor linear growth including dysregulation of the growth hormone/insulin-like growth factor-I (IGF-I) axis, nutritional deficiency, metabolic acidosis, anemia, renal osteodystrophy/bone mineral disease, and inflammation. This review summarizes the causes and assessment tools of growth and nutrition while providing a summary of state of the art therapies for these co-morbidities of pediatric CKD.

Safety, pharmacokinetics and pharmacodynamics of the anti-hepcidin Spiegelmer lexaptepid pegol in healthy subjects

BACKGROUND AND PURPOSE

Anaemia of chronic disease is characterized by impaired erythropoiesis due to functional iron deficiency, often caused by excessive hepcidin. Lexaptepid pegol, a pegylated structured l-oligoribonucleotide, binds and inactivates hepcidin.

EXPERIMENTAL APPROACH

We conducted a placebo-controlled study on the safety, pharmacokinetics and pharmacodynamics of lexaptepid after single and repeated i.v. and s.c. administration to 64 healthy subjects at doses from 0.3 to 4.8 mg·kg(-1) .

KEY RESULTS

After treatment with lexaptepid, serum iron concentration and transferrin increased dose-dependently. Iron increased from approximately 20 μmol·L(-1) at baseline by 67% at 8 h after i.v. infusion of 1.2 mg·kg(-1) lexaptepid. The pharmacokinetics showed dose-proportional increases in peak plasma concentrations and moderately over-proportional increases in systemic exposure. Lexaptepid had no effect on hepcidin production or anti-drug antibodies. Treatment with lexaptepid was generally safe and well tolerated, with mild and transient transaminase increases at doses ≥2.4 mg·kg(-1) and with local injection site reactions after s.c. but not after i.v. administration.

CONCLUSIONS AND IMPLICATIONS

Lexaptepid pegol inhibited hepcidin and dose-dependently raised serum iron and transferrin saturation. The compound is being further developed to treat anaemia of chronic disease.

Iron uptake and ferrokinetics in healthy male subjects of an iron-based oral phosphate binder (SBR759) labeled with the stable isotope (58)Fe

SBR759 is a novel polynuclear iron(III) oxide-hydroxide starch·sucrose·carbonate complex being developed for oral use in chronic kidney disease (CKD) patients with hyperphosphatemia on hemodialysis. SBR759 binds inorganic phosphate released by food uptake and digestion in the gastro-intestinal tract increasing the fecal excretion of phosphate with concomitant reduction of serum phosphate concentrations. Considering the high content of ∼20% w/w covalently bound iron in SBR759 and expected chronic administration to patients, absorption of small amounts of iron released from the drug substance could result in potential iron overload and toxicity. In a mechanistic iron uptake study, 12 healthy male subjects (receiving comparable low phosphorus-containing meal typical for CKD patients: ≤1000 mg phosphate per day) were treated with 12 g (divided in 3 × 4 g) of stable (58)Fe isotope-labeled SBR759. The ferrokinetics of [(58)Fe]SBR759-related total iron was followed in blood (over 3 weeks) and in plasma (over 26 hours) by analyzing with high precision the isotope ratios of the natural iron isotopes (58)Fe, (57)Fe, (56)Fe and (54)Fe by multi-collector inductively coupled mass spectrometry (MC-ICP-MS). Three weeks following dosing, the subjects cumulatively absorbed on average 7.8 ± 3.2 mg (3.8-13.9 mg) iron corresponding to 0.30 ± 0.12% (0.15-0.54%) SBR759-related iron which amounts to approx. 5-fold the basal daily iron absorption of 1-2 mg in humans. SBR759 was well-tolerated and there was no serious adverse event and no clinically significant changes in the iron indices hemoglobin, hematocrit, ferritin concentration and transferrin saturation.

Manipulation of the hepcidin pathway for therapeutic purposes

Hepcidin, the liver-produced peptide hormone, is a principal regulator of iron homeostasis. Abnormal hepcidin production has emerged as a causative factor in several common iron disorders. Hepcidin insufficiency results in iron overload in hereditary hemochromatosis and iron-loading anemias, whereas hepcidin excess causes or contributes to the development of iron-restricted anemias in inflammatory diseases, infections, some cancers and chronic kidney disease. Not surprisingly, hepcidin and related pathways have become the target for the development of novel therapeutics for iron disorders. In this review, we will summarize the strategies and development programs that have been devised for agonizing or antagonizing hepcidin and its receptor ferroportin.

Iron and infection in hemodialysis patients

Intravenous iron is an important component of the treatment of anemia of end-stage renal disease (ESRD), but it is biologically plausible that iron could increase the risk of infection through impairment of neutrophil and T-cell function and promotion of microbial growth. Any such increase in risk would be particularly important because infection is a significant cause of mortality and morbidity in dialysis patients. The overall evidence favors an association between iron and infection in hemodialysis patients, but the optimal iron management strategy to minimize infection risk has yet to be identified. There is a need for further research on this topic, particularly in light of increased utilization of intravenous iron following implementation of the bundled ESRD reimbursement system.

Infection risk with bolus versus maintenance iron supplementation in hemodialysis patients

Intravenous iron may promote bacterial growth and impair host defense, but the risk of infection associated with iron supplementation is not well defined. We conducted a retrospective cohort study of hemodialysis patients to compare the safety of bolus dosing, which provides a large amount of iron over a short period of time on an as-needed basis, with maintenance dosing, which provides smaller amounts of iron on a regular schedule to maintain iron repletion. Using clinical data from 117,050 patients of a large US dialysis provider merged with data from Medicare's ESRD program, we estimated the effects of iron dosing patterns during repeated 1-month exposure periods on risks of mortality and infection-related hospitalizations during the subsequent 3 months. Of 776,203 exposure/follow-up pairs, 13% involved bolus dosing, 49% involved maintenance dosing, and 38% did not include exposure to iron. Multivariable additive risk models found that patients receiving bolus versus maintenance iron were at increased risk of infection-related hospitalization (risk difference [RD], 25 additional events/1000 patient-years; 95% confidence interval [CI], 16 to 33) during follow-up. Risks were largest among patients with a catheter (RD, 73 events/1000 patient-years; 95% CI, 48 to 99) and a recent infection (RD, 57 events/1000 patient-years; 95% CI, 19 to 99). We also observed an association between bolus dosing and infection-related mortality. Compared with no iron, maintenance dosing did not associate with increased risks for adverse outcomes. These results suggest that maintenance iron supplementation may result in fewer infections than bolus dosing, particularly among patients with a catheter.

Efficacy of epigallocatechin-3-gallate and Amla (Emblica officinalis) extract for the treatment of diabetic-uremic patients

Uremic patients with diabetes suffer from high levels of oxidative stress due to regular hemodialysis therapy (neutrophil activation induced by hemo-incompatibility between the hemodialyser and blood) and complications associated with diabetes. Several plasma biomarkers were screened in 13 uremic diabetic patients after receiving the mixture of (-)-epigallocatechin gallate (EGCG), a major component of green tea extract, and Amla extract (AE), from Emblica officinalis, the Indian gooseberry, for 3 months. We found that oral administration of a 1:1 mixture of EGCG and AE for 3 months significantly improved antioxidant defense as well as diabetic and atherogenic indices in uremic patients with diabetes. Furthermore, no significant changes in hepatic function, renal function, or inflammatory responses were observed. These results suggest that a 1:1 combination of EGCG and AE is a safe and effective treatment for uremic patients with diabetes.

Proteinuria induced by parenteral iron in chronic kidney disease--a comparative randomized controlled trial

BACKGROUND AND OBJECTIVES

Among patients with chronic kidney disease (CKD), differences in proteinuria are seen between intravenous iron preparations after a single dose exposure. This study examined differences in proteinuria between two intravenous iron preparations after multiple doses.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with iron-deficiency anemia and CKD, stratified by angiotensin converting enzyme inhibitor (ACEI)/angiotensin receptor-blocker (ARB) use, were randomized to iron sucrose or ferric gluconate. Each patient at 12 centers received 100 mg of study drug weekly for 5 weeks. Urine protein/urine creatinine ratio was measured before each dose and frequently thereafter for 3 hours.

RESULTS

Postbaseline data were available from 33 patients receiving iron sucrose and 29 patients receiving ferric gluconate. Although neither preparation of intravenous iron increased the predose level of proteinuria, the proteinuric response to intravenous iron was dependent on the type of iron and ACEI/ARB use. Without ACEIs/ARBs, ferric gluconate tended to cause less proteinuria with repeated iron administration; iron sucrose did not mitigate or aggravate proteinuria. Among patients receiving ACEIs/ARBs, in contrast to ferric gluconate, which produced only mild transient proteinuria, iron sucrose produced a consistent and persistent proteinuric response that was on average 78% greater.

CONCLUSIONS

Although multiple doses of either intravenous iron did not increase basal levels of proteinuria, postdose proteinuria was greater with iron sucrose than with ferric gluconate. These data suggest that nephrotoxicity of iron may depend on type of intravenous iron and on ACEI/ARB use. The long-term effects on kidney function need to be further evaluated.

FDA report: Ferumoxytol for intravenous iron therapy in adult patients with chronic kidney disease

On June 30, 2009, the United States Food and Drug Administration (FDA) approved ferumoxytol (Feraheme injection, AMAG Pharmaceuticals), an iron-containing product for intravenous (IV) administration, for the treatment of iron deficiency anemia in adult patients with chronic kidney disease (CKD). The safety and efficacy of ferumoxytol were assessed in three randomized, open-label, controlled clinical trials. Two trials evaluated patients with nondialysis dependent CKD and a third trial assessed patients undergoing hemodialysis. Randomization was either to ferumoxytol or oral iron. Ferumoxytol was administered as two 510 mg IV injections, separated by 3-8 days. Oral iron, Ferro-Sequels, was administered at a dose of 100 mg twice daily for 21 days. In all three clinical trials, ferumoxytol administration increased the mean blood hemoglobin (Hgb) concentrations by approximately 1.0 g/dL over the 35 day period, a mean increase that was greater than what was observed in patients receiving oral iron. Patients receiving ferumoxytol also had increases in blood transferrin saturation (TSAT) and ferritin values. For the proposed ferumoxytol dosing regimen, 4.9% of patients had serum ferritin >or=800 ng/mL and TSAT >or=50% post-treatment. The most important ferumoxytol safety concerns were hypersensitivity reactions and/or hypotension. Anaphylaxis or anaphylactoid reactions were reported in 0.2% of subjects, and other adverse reactions potentially associated with hypersensitivity (e.g., pruritus, rash, urticaria, or wheezing) were reported in 3.7%. Hypotension was observed in 1.9%, including three patients with serious hypotensive reactions. Ferumoxytol administration may transiently affect the diagnostic ability of magnetic resonance imaging and the drug label provides further information regarding this effect.

Characterization of a rat model of moderate chronic renal failure--focus on hematological, biochemical, and cardio-renal profiles

The pathophysiological modifications underlying chronic renal failure seems to be dependent on the insufficiency degree, which will determine the moment to start therapy. As there is yet limited information about animal models of moderate chronic renal failure, we intended to perform a complete characterization of the hematological and cardio-renal alterations induced by partial nephrectomy. Blood samples from control and chronic renal failure rats were collected at 0, 3, 9, and 15 weeks in order to evaluate renal function, hematological parameters, iron metabolism, blood lipids, peripheral sympathetic nervous system, and inflammatory and redox status markers. BP, tissues trophy indexes, and kidney histomorphology were also assessed. Our data are consistent with a sustained moderate degree of chronic renal failure with a quickly compensated modest anaemia, though presenting iron metabolism disturbances. Despite the reasonable degree of functionality of the remnant kidney, as suggested by the anaemia correction and by the kidney hypertrophy and moderate lesions, several important cardiovascular modifications were developed. Our model presented hypertension, dyslipidemia, erythropoietic disturbances, sympathetic activation, and oxidative stress. This model might be a good tool to study the cellular/molecular mechanisms underlying moderate stages of chronic renal failure and to evaluate the therapeutic efficacy for prevention and treatment/correction of cardio-renal anaemia syndromes and complications in early stages.

Gene therapy by electroporation for the treatment of chronic renal failure in companion animals

Background

Growth hormone-releasing hormone (GHRH) plasmid-based therapy for the treatment of chronic renal failure and its complications was examined. Companion dogs (13.1 ± 0.8 years, 29.4 ± 5.01 kg) and cats (13.2 ± 0.9 years, 8.5 ± 0.37 kg) received a single 0.4 mg or 0.1 mg species-specific plasmid injection, respectively, intramuscularly followed by electroporation, and analyzed up to 75 days post-treatment; controls underwent electroporation without plasmid administration.

Results

Plasmid-treated animals showed an increase in body weight (dogs 22.5% and cats 3.2%) compared to control animals, and displayed improved quality of life parameters including significant increases in appetite, activity, mentation and exercise tolerance levels. Insulin-like growth factor I (IGF-I, the downstream effector of GHRH) levels were increased in the plasmid treated animals. Hematological parameters were also significantly improved. Protein metabolism changes were observed suggesting a shift from a catabolic to an anabolic state in the treated animals. Blood urea nitrogen and creatinine did not show any significant changes suggesting maintenance of kidney function whereas the control animal's renal function deteriorated. Treated animals survived longer than control animals with 70% of dogs and 80% of cats surviving until study day 75. Only 17% and 40% of the control dogs and cats, respectively, survived to day 75.

Conclusion

Improved quality of life, survival and general well-being indicate that further investigation is warranted, and show the potential of a plasmid-based therapy by electroporation in preventing and managing complications of renal insufficiency.

Characterization and differentiation of iron status in anemic very low birth weight infants using a diagnostic nomogram

BACKGROUND

In the early weeks of life, very low birth weight (VLBW) infants experience intense laboratory blood sampling leading to clinically significant anemia and the need for red blood cell transfusion. Although controversial, treatment with recombinant human erythropoietin (EPO) and iron has been recommended to stimulate erythropoiesis; optimal dosing of EPO and iron is still uncertain.

OBJECTIVES

To assess the validity of a four-quadrant diagnostic plot of iron availability (ferritin index) versus iron demand for erythropoiesis (reticulocyte hemoglobin content, CHr) for differentiating iron status in anemic VLBW infants.

METHODS

Study subjects were enrolled in a previously reported randomized controlled trial of clinically stable VLBW infants <31 weeks' gestation and <1,300 g at birth to receive 18 days of treatment with: group 1: oral iron; group 2: EPO + oral iron, and group 3: EPO + intravenous + oral iron.

RESULTS

At the end of treatment the ferritin index was significantly higher in both EPO groups compared to the control group. By day 18, CHr of the control group declined into the quadrant of the diagnostic plot characteristic of functional iron deficiency and anemia of chronic disease. Both EPO groups ended in the quadrants that are characteristic for latent iron deficiency and iron deficiency anemia, respectively.

CONCLUSIONS

The diagnostic plot for differentiating anemia in VLBW infants may be an informative, clinically useful tool for iron status assessment under different physiologic and therapeutic erythropoietic states. Larger additional studies in difficult patient populations are needed before the clinical utility of this diagnostic procedure can be unequivocally confirmed.

Iron, oxidative stress, and clinical outcomes

It is well known that iron is pro-oxidant. Chronic kidney disease (CKD) is a pro-oxidant state, and intravenous administration of iron is frequently used to correct anemia. On one hand, there is little doubt that iron causes oxidative stress. On the other, it is far from clear whether oxidative stress, so generated, leads to poor clinical outcomes. Iron has benefits that may be independent of the correction of anemia. Furthermore, concerns surround the use of high doses of erythropoietin in causing excess heart failure and death in patients with CKD. Thus, it would be prudent if iron were to continue to be used judiciously in patients who require erythropoietin. Iron, given orally, would be the preferred first-line agent in patients not on hemodialysis. In patients with sepsis, intravenous treatment with iron should be avoided, because, in animal experiments, intravenous administration of iron can compound the inflammatory response and increase mortality. Clinical trials are needed to ascertain the risk and benefits of the intravenous administration of iron in patients with CKD.

Comparative toxicity and cell-tissue distribution study on nanoparticular iron complexes using avian embryos and HepG2-cells

In this study the toxicity and intracellular availability of iron from iron dextran (FeD), iron sucrose (FeS), and iron gluconate (FeG) was compared in organs of avian (turkey) embryos and in isolated cells (HepG2) in cell culture. Iron uptake was more pronounced in embryonic liver than in renal tissue. Cellular iron uptake in liver and kidney was more or less similar for the different compounds. Only some experiments showed slightly greater iron concentrations in liver and kidney with FeG compared with FeD and FeS. Significant differences were found in the survival ratios of the eggs and the embryo weights depending on the type of iron complex administered. The rank order of toxicities was FeG>FeS>FeD. Iron accumulation in HepG2-cells was extremely high with FeS and FeG, whereas FeD did not lead to a relevant iron uptake by HepG2 cells. The excessively high iron content of the cells is an in vitro phenomenon found neither in the in ovo model with the turkey embryos nor in the clinical use of the compounds. The rank order of toxicities in HepG2 cells was FeS>FeG>FeD. Iron uptake in cell culture does not reflect the in vivo situation. The in ovo model is more suitable to assess the cellular iron uptake and iron toxicity in cells and tissues than the in vitro model. In both in ovo and in vitro experiments, FeD seemed to be superior in terms of toxicity.