Severe FGF23-based hypophosphataemic osteomalacia due to ferric carboxymaltose administration

[Iron supplementation in patients with chronic inflammatory bowel disease: recommendations for a practical approach]

Iron deficiency is the predominant cause of anemia. Iron deficiency anemia plays a major role, especially in patients with inflammatory bowel disease (IBD), and is the most common extraintestinal manifestation and IBD-associated systemic complication. The presence of anemia leads to a reduction in quality of life in patients with IBD associated with limitations in physical, emotional, and cognitive function. In addition, it is associated with an increased hospitalization rate. For this reason, iron supplementation is of particular importance. Oral and intravenous iron supplements are used to treat iron deficiency. Due to the lack of absorption and gastrointestinal side effects of oral substitution, intravenous supplementation is becoming increasingly important. However, there are still certain concerns about intravenous administration.With the help of this review, we want to address the topic of iron substitution in patients with IBD, summarize current guideline recommendations, and provide a practical approach.

Ironing It All Out: A Comprehensive Review of Iron Deficiency Anemia in Inflammatory Bowel Disease Patients

Iron deficiency anemia affects approximately 45% of patients with inflammatory bowel disease (IBD), negatively impacts the quality of life in this patient population, and significantly burdens our healthcare system. The pathogenesis of iron deficiency in IBD patients is multifactorial, including intestinal bleeding, malabsorption, and inadequate oral intake. Regular screening and diagnosis in these patients are imperative, and often patients have mixed iron deficiency anemia and anemia of chronic disease, especially in those with active inflammation. Iron may be replenished either orally or intravenously. While oral iron is safe, affordable, and easy to administer, patients often suffer from intolerable gastrointestinal side effects, and particularly in IBD patients, oral iron may increase inflammation and contribute to flares. Therefore, although it is substantially underused, intravenous (IV) iron is considered first-line treatment for patients with active disease, severe anemia, oral iron intolerance, and erythropoietin requirements. Several IV iron formulations are available, and iron sucrose and ferric carboxymaltose are the most frequently used and well studied in patients with IBD. However, iron isomaltoside could potentially become a popular choice among providers given its safety, efficacy, and convenience. Overall, screening, diagnosis, and treatment of iron deficiency anemia are important in patients with IBD. Individual patient characteristics, risks, and benefits, and advantages and disadvantages, should be considered when determining the best route and formulation for iron repletion.

High-Dose Intravenous Iron with Either Ferric Carboxymaltose or Ferric Derisomaltose: A Benefit-Risk Assessment

The intravenous iron formulations ferric carboxymaltose (FCM) and ferric derisomaltose (FDI) offer the possibility of administering a large amount of iron in one infusion. This results in faster correction of anemia and the formulations being better tolerated than oral iron formulations. This triad of logistic advantages, improved patient convenience, and fast correction of anemia explains the fact that intravenous iron formulations nowadays are frequently prescribed worldwide in the treatment of iron deficiency anemia. However, these formulations may result in hypophosphatemia by inducing a strong increase in active fibroblast growth factor-23 (FGF-23), a hormone that stimulates renal phosphate excretion. This effect is much more pronounced with FCM than with FDI, and therefore the risk of developing hypophosphatemia is remarkably higher with FCM than with FDI. Repeated use of FCM may result in severe osteomalacia, which is characterized by bone pain, Looser zones (pseudofractures), and low-trauma fractures. Intravenous iron preparations are also associated with other adverse effects, of which hypersensitivity reactions are the most important and are usually the result of a non-allergic complement activation on nanoparticles of free labile iron-Complement Activation-Related Pseudo-Allergy (CARPA). The risk on these hypersensitivity reactions can be reduced by choosing a slow infusion rate. Severe hypersensitivity reactions were reported in < 1% of prospective trials and the incidence seems comparable between the two formulations. A practical guideline has been developed based on baseline serum phosphate concentrations and predisposing risk factors, derived from published cases and risk factor analyses from trials, in order to establish the safe use of these formulations.

Risk Factors for and Effects of Persistent and Severe Hypophosphatemia Following Ferric Carboxymaltose

CONTEXT

Hypophosphatemia, osteomalacia, and fractures are complications of certain intravenous iron formulations.

OBJECTIVE

This study investigated risk factors for incident, severe, and persistent hypophosphatemia, and associated alterations in bone and mineral biomarkers following intravenous iron treatment.

METHODS

We analyzed data from the PHOSPHARE-IDA randomized clinical trials, comprising 245 patients aged 18 years or older with iron deficiency anemia at 30 outpatient clinics in the United States who received intravenous ferric carboxymaltose (FCM) or ferric derisomaltose (FDI). Outcome measures included serum phosphate, intact fibroblast growth factor-23 (iFGF23), 1,25-dihydroxyvitamin D (1,25(OH)2D), ionized calcium, parathyroid hormone (PTH), and alkaline phosphatase.

RESULTS

FCM was the only consistent risk factor for incident hypophosphatemia (< 2.0 mg/dL; odds ratio vs FDI: 38.37; 95% CI: 16.62, 88.56; P < 0.001). Only FCM-treated patients developed severe hypophosphatemia (< 1.0 mg/dL; 11.3%; 13/115) or persistent hypophosphatemia (< 2.0 mg/dL at study end; 40.0%; 46/115). More severe hypophosphatemia associated with significantly greater increases in iFGF23, PTH, and alkaline phosphatase, and more severe decreases in 1,25(OH)2D and ionized calcium (all P < 0.05). Patients with persistent vs resolved hypophosphatemia demonstrated significantly greater changes in iFGF23, PTH, 1,25(OH)2D, and N-terminal procollagen-1 peptide levels (all P < 0.01), but alkaline phosphatase increased similarly in both groups.

CONCLUSION

Treatment with FCM was the only consistent risk factor for hypophosphatemia. Patients who developed severe or persistent hypophosphatemia after FCM treatment manifested more severe derangements in bone and mineral metabolism. Changes in bone biomarkers continued beyond resolution of hypophosphatemia, suggesting ongoing effects on bone that may help explain the association of FCM with osteomalacia and fractures.

Intravenous Iron-Induced Hypophosphatemia: An Emerging Syndrome

Some, but not all, intravenous iron formulations have been recognized to induce renal phosphate wasting syndrome. Most commonly this has been reported following treatment of iron deficiency anemia (IDA) with ferric carboxymaltose (FCM). A search of PubMed identified relevant randomized controlled trials (RCTs), and case studies evaluating hypophosphatemia (HPP) resulting from intravenous iron treatment. While more recent larger comparative RCTs have confirmed that the majority of patients receiving FCM, especially those with normal renal function, may experience severe HPP, complete documentation is hampered by inconsistent reporting of serum phosphate in such trials. Similarly, while case series and RCTs have documented the persistence of HPP for several weeks or even months, the lack of studies lasting beyond 5–6 weeks has constrained full understanding of the duration of effect. Clinical trials have established that the mechanism involves the bone/metabolic axis with the elevation of intact fibroblast growth factor 23 playing the central role. Reports continue to accumulate of the clinical consequences of severe HPP which are, most commonly, bone abnormalities following repetitive dosing. Case reports and studies, however, have also shown that symptomatic hypophosphatemia can occur after a single FCM dose. The frequency of such events remains unknown, in part due to lack of awareness of hypophosphatemia coupled with the fact that the most common acute symptoms of HPP (fatigue and weakness) are the same for IDA and for many of the chronic diseases that cause IDA. Changes to US and European prescribing information for FCM should raise awareness of the potential for HPP and need to monitor patients at risk for it.

The HIF-PHI BAY 85-3934 (Molidustat) Improves Anemia and Is Associated With Reduced Levels of Circulating FGF23 in a CKD Mouse Model

Fibroblast growth factor-23 (FGF23) is a critical factor in chronic kidney disease (CKD), with elevated levels causing alterations in mineral metabolism and increased odds for mortality. Patients with CKD develop anemia as the kidneys progressively lose the ability to produce erythropoietin (EPO). Anemia is a potent driver of FGF23 secretion; therefore, a hypoxia-inducible factor prolyl hydroxylase inhibitor (HIF-PHI) currently in clinical trials to elevate endogenous EPO to resolve anemia was tested for effects on iron utilization and FGF23-related parameters in a CKD mouse model. Mice were fed either a casein control diet or an adenine-containing diet to induce CKD. The CKD mice had markedly elevated iFGF23 and blood urea nitrogen (BUN), hyperphosphatemia, and anemia. Cohorts of mice were then treated with a patient-equivalent dose of BAY 85-3934 (BAY; Molidustat), which elevated EPO and completely resolved aberrant complete blood counts (CBCs) in the CKD mice. iFGF23 was elevated in vehicle-treated CKD mice (120-fold), whereas circulating iFGF23 was significantly attenuated (>60%) in the BAY-treated CKD mice. The BAY-treated mice with CKD also had reduced BUN, but there was no effect on renal vitamin D metabolic enzyme expression. Consistent with increased EPO, bone marrow Erfe, Transferrin receptor (Tfrc), and EpoR mRNAs were increased in BAY-treated CKD mice, and in vitro hypoxic marrow cultures increased FGF23 with direct EPO treatment. Liver Bmp-6 and hepcidin expression were downregulated in all BAY-treated groups. Femur trabecular parameters and cortical porosity were not worsened with BAY administration. In vitro, differentiated osteocyte-like cells exposed to an iron chelator to simulate iron depletion/hypoxia increased FGF23; repletion with holo-transferrin completely suppressed FGF23 and normalized Tfrc1. Collectively, these results support that resolving anemia using a HIF-PHI during CKD was associated with lower BUN and reduced FGF23, potentially through direct restoration of iron utilization, thus providing modifiable outcomes beyond improving anemia for this patient population. © 2021 American Society for Bone and Mineral Research (ASBMR).

Newer formulations of intravenous iron: a review of their chemistry and key safety aspects - hypersensitivity, hypophosphatemia, and cardiovascular safety

Introduction: The newest intravenous (IV) iron products show an improved safety profile over predecessors, allowing for the rapid administration of relatively high doses. Ferric derisomaltose (FDI; also known as iron isomaltoside), ferric carboxymaltose (FCM), and ferumoxytol (FER), are successful treatments for iron deficiency (Europe; FDI and FCM) and iron deficiency anemia (US; FDI, FCM, and FER).Areas covered: This review focusses on the chemistry and structure of FDI, FCM, and FER, and on three key aspects of IV iron safety: (1) hypersensitivity; (2) hypophosphatemia and sequelae; (3) cardiovascular safety.Expert opinion: Although the safety of modern IV iron has improved, immediate infusion reactions and the development of hypophosphatemia must be appreciated and recognized by those who prescribe and administer IV iron. Immediate infusion reactions can occur with any IV iron and are usually mild; severe reactions - particularly anaphylaxis - are extremely rare. The recognition and appropriate management of infusion reactions is an important consideration to the successful administration of IV iron. Severe, persistent, hypophosphatemia is a specific side effect of FCM. No cardiovascular safety signal has been identified for IV iron. Ongoing trials in heart failure will provide additional long-term efficacy and safety data.

Are Pregnant Women Who Are Living with Overweight or Obesity at Greater Risk of Developing Iron Deficiency/Anaemia?

Low-grade inflammation is often present in people living with obesity. Inflammation can impact iron uptake and metabolism through elevation of hepcidin levels. Obesity is a major public health issue globally, with pregnant women often affected by the condition. Maternal obesity is associated with increased pregnancy risks including iron deficiency (ID) and iron-deficiency anaemia (IDA)-conditions already highly prevalent in pregnant women and their newborns. This comprehensive review assesses whether the inflammatory state induced by obesity could contribute to an increased incidence of ID/IDA in pregnant women and their children. We discuss the challenges in accurate measurement of iron status in the presence of inflammation, and available iron repletion strategies and their effectiveness in pregnant women living with obesity. We suggest that pre-pregnancy obesity and overweight/obese pregnancies carry a greater risk of ID/IDA for the mother during pregnancy and postpartum period, as well as for the baby. We propose iron status and weight gain during pregnancy should be monitored more closely in women who are living with overweight or obesity.

Hypophosphatemia after high-dose intravenous iron treatment in patients with inflammatory bowel disease: Mechanisms and possible clinical impact

BACKGROUND

High-dose intravenous iron is an effective treatment option for iron deficiency (ID) or ID anaemia (IDA) in inflammatory bowel disease (IBD). However, treatment with ferric carboxymaltose (FCM) has been associated with the development of hypophosphatemia.

AIM

To investigate mechanisms behind the development of hypophosphatemia after intravenous iron treatment, and disclose symptoms and clinical manifestations related to hypophosphatemia short-term.

METHODS

A prospective observational study of adult IBD patients with ID or IDA was conducted between February 1, 2017 and July 1, 2018 at two separate university hospitals in the southeast region of Norway. Patients received one dose of 1000 mg of either FCM or ferric derisomaltose (FDI) and were followed for an observation period of at least 7 wk. Blood and urine samples were collected for relevant analyses at baseline, week 2 and at week 6. Clinical symptoms were assessed at the same timepoints using a respiratory function test, a visual analogue scale, and a health-related quality of life questionnaire.

RESULTS

A total of 106 patients was available for analysis in this study. The FCM treatment group consisted of 52 patients and hypophosphatemia was present in 72.5% of the patients at week 2, and in 21.6% at week 6. In comparison, the FDI treatment group consisted of 54 patients and 11.3% of the patients had hypophosphatemia at week 2, and 3.7% at week 6. The difference in incidence was highly significant at both week 2 and 6 (P < 0.001 and P < 0.013, respectively). We observed a significantly higher mean concentration of intact fibroblast growth factor 23 (P < 0.001), a significant rise in mean urine fractional excretion of phosphate (P = 0.004), a significant decrease of 1,25-dihydroxyvitamin D (P < 0.001) and of ionised calcium levels (P < 0.012) in the FCM-treated patients compared with patients who received FDI. No clinical symptoms could with certainty be related to hypophosphatemia, since neither the respiratory function test, SF-36 (36-item short form health survey) or the visual analogue scale scores resulted in significant differences between patients who developed hypophosphatemia or not.

CONCLUSION

Fibroblast growth factor 23 has a key role in FCM induced hypophosphatemia, probably by inducing loss of phosphate in the urine. Short-term clinical impact of hypophosphatemia was not demonstrated.

Parenteral iron therapy and phosphorus homeostasis: A review

Phosphorus has an essential role in cellular and extracellular metabolism; maintenance of normal phosphorus homeostasis is critical. Phosphorus homeostasis can be affected by diet and certain medications; some intravenous iron formulations can induce renal phosphate excretion and hypophosphatemia, likely through increasing serum concentrations of intact fibroblast growth factor 23. Case studies provide insights into two types of hypophosphatemia: acute symptomatic and chronic hypophosphatemia, while considering the role of pre‐existing conditions and comorbidities, medications, and intravenous iron. This review examines phosphorus homeostasis and hypophosphatemia, with emphasis on effects of iron deficiency and iron replacement using intravenous iron formulations.

Hypophosphataemia, fibroblast growth factor 23 and third-generation intravenous iron compounds: a narrative review

Third-generation intravenous (i.v.) iron preparations are safe and efficacious and are increasingly used in the treatment of iron-deficiency anaemia. Hypophosphataemia is emerging as an established side-effect following the administration of certain compounds. Symptoms of hypophosphataemia can be masked by their similarity to those of iron-deficiency anaemia and both acute and chronic hypophosphataemia can be detrimental. Hypophosphataemia appears to be linked to imbalances in the metabolism of the phosphatonin fibroblast growth factor 23. In this narrative review, we discuss the possible pathophysiology behind this phenomenon, the studies comparing third-generation i.v. iron compounds, and the potential implications of the changes in fibroblast growth factor 23 and hypophosphataemia. We also present an algorithm of how to approach such patients requiring i.v. iron in anticipation of hypophosphataemia and how the impact related to it can be minimized.

A Normal FGF23 Does Not Preclude Tumor-Induced Osteomalacia

Tumor-induced osteomalacia (TIO) is a rare cause of impaired bone mineralization mediated by the osteocyte-derived, phosphaturic hormone: fibroblast growth factor 23 (FGF23). The case is presented of a previously healthy 45-year-old man who developed fragility fractures at multiple sites (initially metatarsals, eventually ribs, hips, spine, scapula, and sacrum) resulting in rapid functional deterioration, weakness, and the inability to bear weight and ambulate without a walker. Workup for secondary causes of bone loss was negative except for mild hypogonadotropic hypogonadism with normal pituitary MRI and hypophosphatemia that persisted despite aggressive supplementation. Testosterone was initiated but discontinued 6 months later because of deep vein thrombosis and pulmonary embolism, likely provoked by his new sedentary state, in addition to smoking history and possibly testosterone usage. Serum FGF23 was nonelevated at 138 mRU/mL (44-215). A genetic panel for OI variants was negative for a causal mutation. At the age of 48, 3 years after his initial fracture, he was referred to our academic endocrine clinic. We ruled out additional mutations that lead to hypophosphatemic rickets, including phosphate-regulating endopeptidase homolog, X-linked. PET/CT looking for a potential TIO locus revealed uptake in the left suprapatellar recess. Biopsy was consistent with a phosphaturic mesenchymal tumor. FGF23 was repeated for a preoperative baseline and now found to be elevated at 289 mRU/mL. In retrospect, it is likely that the initial level was inappropriately elevated for the degree of hypophosphatemia. After resection, he experienced marked improvement in physical function, decreased pain, and resolution of renal phosphate wasting. The principals of establishing a robust clinical diagnosis of TIO should be emphasized, excluding other entities and avoiding pitfalls in the interpretation of laboratory testing. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Effects of ferric carboxymaltose on markers of mineral and bone metabolism: A single-center prospective observational study of women with iron deficiency

BACKGROUND

Two weekly infusions of ferric carboxymaltose (FCM) are commonly prescribed for treatment of iron-deficiency anemia. However, administration of FCM increases intact levels of fibroblast growth factor 23 (FGF23), which causes hypophosphatemia due to renal phosphate wasting, calcitriol deficiency and secondary hyperparathyroidism. The adverse effects of FCM on mineral metabolism and bone health emerged from case reports and secondary analyses of trials. Data on these safety signals with FCM in clinical practice are limited because markers of mineral and bone metabolism are not routinely checked.

METHODS

To obtain real-world experience with effects of FCM on mineral and bone metabolism, we conducted a prospective observational study of 16 women who were managed at a single-center hematology clinic for iron-deficiency anemia. From October 2016 to February 2018, all participants received two weekly infusions of FCM at a hematology infusion clinic. We hypothesized that FCM would decrease phosphate, increase intact FGF23 (iFGF23), and decrease c-terminal FGF23 (cFGF23). Secondary outcomes were changes in hemoglobin, iron indices, urine fractional excretion of phosphate (FePi), parathyroid hormone (PTH), calcitriol, calcium, osteocalcin, and bone-specific alkaline phosphatase (BAP). FCM was administered at weeks zero and one, and we measured laboratory values at weeks zero, one, two, and five of the study. We used linear mixed models to analyze the significance of the changes in laboratory values over time.

RESULTS

After two FCM infusions, nearly all (14 of 16) participants developed hypophosphatemia. iFGF23 increased, cFGF23 decreased, and phosphate decreased significantly from week zero to week two (iFGF23 increased by +134.0% [40.6, 305.8], p < 0.001; cFGF23 decreased by -516.3% [-1332.7, -142.7], p = 0.002; phosphate decreased by -49.8 ± 15.4%, p < 0.001). There was also a significant increase in FePi, PTH, and BAP and a significant decrease in calcitriol and calcium from week zero to week two. There was no significant change in osteocalcin during this time period. iFGF23, but not PTH, was independently associated with decreased phosphate. iFGF23 was also significantly associated with decrease in calcitriol from week zero to week two. Elevation in BAP suggests disordered bone mineralization in response to FCM therapy.

CONCLUSION

In this prospective observational study of women with iron deficiency anemia, two FCM infusions significantly altered markers of bone mineralization and mineral metabolism. The results suggest that FCM should be used cautiously in the treatment of iron-deficiency anemia.

A Pooled Analysis of Serum Phosphate Measurements and Potential Hypophosphataemia Events in 45 Interventional Trials with Ferric Carboxymaltose

Ferric carboxymaltose (FCM) has been shown to achieve rapid replenishment of iron stores and correction of anaemia in various populations with iron deficiency. A decrease in serum phosphate (PO₄³⁻) levels, which in most cases is asymptomatic, has been reported with IV iron preparations. Hypophosphataemia (HP) is a known adverse drug reaction with FCM. This post hoc pooled analysis investigates the frequency, duration, risk factors, and clinical signs of HP as reported in interventional clinical trials with FCM. Pooled data from subjects enrolled across 45 clinical trials in different therapy areas were included. A three-step adjudication process was utilised to identify adverse events of HP. Stratified analyses by therapy group and stepwise logistic regression analysis were used to identify predictors of HP. This pooled analysis confirms that FCM is associated with increased rates of serum PO₄³⁻ lowering, but mean serum PO₄³⁻ values were seen to recover at Week 4 and further recover at Week 8. Among all subjects receiving FCM therapy (n = 6879), 41.4% (n = 2847) reached a PO₄³⁻ nadir value <2.5 mg/dL at any point on study and 0.7% (n = 49) reached a nadir <1 mg/dL. Although gastroenterology and women’s health subjects were identified to be at higher risk, occurrence of severe HP (<1 mg/dL [0.3 mmol/L]) following FCM administration was not observed to be common among subjects in these studies. Furthermore, there was no correlation between laboratory serum PO₄³⁻ values and the occurrence of reported adverse events related to low PO₄³⁻ levels.

Severe osteomalacia with multiple insufficiency fractures secondary to intravenous iron therapy in a patient with Rendu-Osler-Weber syndrome

Summary

This case report describes a 65-year-old man with a Rendu-Osler-Weber syndrome with secondary chronic anaemia, who received multiple intravenous (IV) iron infusions and sustained diffuse bone pain secondary to multiple insufficiency fractures. Laboratory study confirmed fibroblast growth factor 23 (FGF-23)-mediated hypophosphatemia as the main cause of a severe osteomalacia induced by ferric carboxymaltose (FCM).

After 3 months or oral phosphate replacement and switching to iron sucrose, serum phosphate levels were normalized and patient improved clinically.

Introduction

Some drugs can induce asymptomatic hypophosphatemia, which if sustained, can lead to a severe osteomalacia with multiple skeletal fractures. This complication has also been described with IV iron therapy.

Methods

This case report describes a patient with Rendu-Osler-Weber syndrome with chronic iron deficiency anaemia, recurrently treated with FCM, who developed a severe osteomalacia with multiple skeletal fractures.

Results

Laboratory study showed hypophosphatemia, with high ALP and high FGF-23. Images studies confirmed bone mass loss and multiple insufficiency fractures. A Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) did not show hidden tumor, so a diagnosis of FCM-induced hypophosphatemic osteomalacia was performed. Phosphate replacement improved clinical symptoms of the patient.

Conclusion

Intravenous iron therapy, mainly FCM form, can cause hypophosphatemia, and in some cases induce a severe osteomalacia with multiple fractures, so it seems advisable to monitor serum phosphate levels in high risk patients, as those who receive repeated dose.

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Intravenous iron therapy can cause hypophosphatemia and in some cases osteomalacia.

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Ferric carboxymaltose can raise fibroblast growth factor 23, a phosphaturic hormone.

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Osteomalacia should be considered if a patient treated with iron therapy develops pain.

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It's advisable to monitor serum phosphate in patients who receive iron therapy.

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In case of persistent hypophosphatemia, switch to another iron therapy is suggested.

Comparative Risk of Hypophosphatemia Following the Administration of Intravenous Iron Formulations: A Network Meta-Analysis

Intravenous iron therapy is increasingly used in patients with iron deficiency anemia, although concerns of hypophosphatemia have been recently raised. The aim of this study was to evaluate different intravenous iron formulations for the risk of hypophosphatemia. Medline, Scopus, Cochrane Central Register of Controlled Trials, Web of Science, Clinicaltrials.gov, and Google Scholar databases were systematically searched to 20 March 2020. All randomized controlled trials reporting the incidence of hypophosphatemia among adult patients treated with any intravenous iron preparation were included. Pool estimates were obtained by applying an arm-based Bayesian network meta-analysis model. Eight randomized controlled trials were included, comprising 5989 patients. Ferric carboxymaltose was associated with significantly higher incidence of hypophosphatemia compared to iron isomaltoside (risk ratio [RR]: 7.90, 95% confidence interval [CI]: 2.10-28.0), iron sucrose (RR: 9.40, 95% CI: 2.30-33.0), iron dextran (RR: 6.60, 95% CI: 1.91-220.0), and ferumoxytol (RR: 24.0, 95% CI: 2.50-220.0). Therefore, ferric carboxymaltose ranked as the worst treatment presenting the highest surface under the cumulative ranking curve (99.1%). No significant differences were estimated for the comparisons among iron isomaltoside, iron sucrose, iron dextran, and ferumoxytol. In conclusion, it is suggested that the occurrence of hypophosphatemia is common after the administration of intravenous ferric carboxymaltose. Further research is needed in large-scale randomized controlled trials to determine the risk of symptomatic and persistent hypophosphatemia as well as to elucidate the exact pathophysiology of the observed association.

Hypophosphatemia Associated with Intravenous Iron Therapies for Iron Deficiency Anemia: A Systematic Literature Review

Background

Iron deficiency anemia (IDA) is a prevalent yet underdiagnosed condition with a significant impact on quality of life. Oral iron supplementation is often poorly tolerated or yields inadequate response, requiring the use of intravenous iron (IVI) in some patients. Administration of certain IVI preparations has been associated with decreases in serum phosphate levels and clinically significant hypophosphatemia, which has been reported to lead to adverse events including serious fatigue and osteomalacia.

Objective

The purpose of this study was to systematically assess the prevalence, clinical consequences, and reporting of treatment-emergent hypophosphatemia within literature investigating IVI therapies marketed in the United States (US).

Methods

A systematic literature review (SLR) was conducted using the PubMed database to identify publications reporting serum phosphate levels or rates of hypophosphatemia within adult IDA patient populations receiving current US-marketed IVIs.

Results

The SLR yielded 511 unique publications, with 40 records meeting the final inclusion criteria. Most studies did not report phosphate monitoring methodology or an explicit definition of hypophosphatemia. Hypophosphatemia rates ranged from 0.0% to 92.1% for ferric carboxymaltose (FCM), 0.0% to 40.0% for iron sucrose, 0.4% for ferumoxytol, and 0.0% for low-molecular-weight (LMW) iron dextran. Randomized controlled studies described hypophosphatemia as “asymptomatic” or did not report on other associated sequelae. Eleven case reports detailed treatment-emergent hypophosphatemia in patients treated with FCM. Patients with acute hypophosphatemia primarily developed severe fatigue; those with repeated FCM dosing developed chronic hypophosphatemia associated with osteomalacia and bone deformities.

Conclusion

Studies analyzed in this SLR reported a range of hypophosphatemia rates, with the highest consistently seen in patients treated with FCM. Across the clinical literature, there appeared to be minimal standardization of phosphate monitoring and definitions of hypophosphatemia. Although multiple cases have documented serious clinical consequences of hypophosphatemia associated with certain IVIs, current trials neither consistently nor adequately assess the frequency and severity of treatment-emergent hypophosphatemia and may underestimate its prevalence.

Crosstalk between fibroblast growth factor 23, iron, erythropoietin, and inflammation in kidney disease

PURPOSE OF REVIEW

Recent research has revealed that regulation of the bone-secreted hormone fibroblast growth factor 23 (FGF23) is not limited to classical mineral factors. Specifically, bidirectional relationships have been described between FGF23 production and anemia, iron status, and inflammation. Here, we will review the latest published articles on the crosstalk between FGF23 and the aforementioned nonclassical factors.

RECENT FINDINGS

It has been recently reported that erythropoietin, iron deficiency, and inflammation increase FGF23 production and metabolism. Moreover, FGF23 promotes anemia and regulates inflammatory responses. These findings are particularly important in the setting of chronic kidney disease which is characterized by elevated FGF23 levels and several associated comorbidities.

SUMMARY

Regulation of FGF23 is complex and involves many bone and renal factors. More recently, erythropoietin, iron deficiency, and inflammation have been also shown to affect FGF23 transcription and cleavage. Importantly, FGF23 has emerged as a regulator of erythropoiesis, iron metabolism, and inflammation. These findings provide novel and important insights into the pathophysiologic mechanisms of chronic kidney disease and may present new opportunities for therapeutic clinical interventions.

High Risk of Hypophosphatemia in Patients with Previous Bariatric Surgery Receiving Ferric Carboxymaltose: A Prospective Cohort Study

BACKGROUND

Iron deficiency is a common finding in patients with previous bariatric surgery, and parenteral supplementation is frequently required. Ferric carboxymaltose (FCM) is among the preferred compounds used but may be associated with new-onset hypophosphatemia. This study was undertaken to study the prevalence of hypophosphatemia following FCM in patients with previous bariatric surgery, a population that may be at particular risk due to highly prevalent secondary hyperparathyroidism.

METHODS

Patients with previous bariatric surgery and iron depletion scheduled for FCM infusion were prospectively studied before and one week after FCM application. The primary endpoint was new-onset hypophosphatemia. Patients were followed until plasma phosphate had normalized without replacement.

RESULTS

Fifty-two patients (40 females) following Roux-en-Y gastric bypass (n = 50) or sleeve gastrectomy (n = 2), with a median age of 46 years (range 22-68) and a BMI of 32.2 kg/m² (27.5-37.3), were analyzed. Fifteen patients (29%) developed new-onset hypophosphatemia, with 11 (21%) requiring oral phosphate supplementation for a median duration of 14 days (14-25). The plasma phosphate decreased by 0.3 mmol/l (-0.5--0.2; p < 0.001) secondary to a 56% increase in the fractional urinary phosphate excretion (p < 0.001). This was associated with a significant increase in serum intact FGF23 (+30%; p < 0.001) and a decrease in serum 1,25(OH)2 vitamin D3 concentrations (-37.6%; p < 0.001).

CONCLUSION

Patients with previous bariatric surgery receiving FCM are at considerable risk of developing significant hypophosphatemia secondary to increased renal phosphate wasting through a mechanism involving FGF23. Monitoring plasma phosphate should be considered following FCM in patients with previous bariatric surgery.

CLINICAL TRIAL REGISTRATION

ISRCTN registry, ISRCTN12291677, https://www.isrctn.com.

Effects of Iron Isomaltoside vs Ferric Carboxymaltose on Hypophosphatemia in Iron-Deficiency Anemia: Two Randomized Clinical Trials

Importance

Intravenous iron enables rapid correction of iron-deficiency anemia, but certain formulations induce fibroblast growth factor 23-mediated hypophosphatemia.

Objective

To compare risks of hypophosphatemia and effects on biomarkers of mineral and bone homeostasis of intravenous iron isomaltoside (now known as ferric derisomaltose) vs ferric carboxymaltose.

Design, Setting, and Participants

Between October 2017 and June 2018, 245 patients aged 18 years and older with iron-deficiency anemia (hemoglobin level ≤11 g/dL; serum ferritin level ≤100 ng/mL) and intolerance or unresponsiveness to 1 month or more of oral iron were recruited from 30 outpatient clinic sites in the United States into 2 identically designed, open-label, randomized clinical trials. Patients with reduced kidney function were excluded. Serum phosphate and 12 additional biomarkers of mineral and bone homeostasis were measured on days 0, 1, 7, 8, 14, 21, and 35. The date of final follow-up was June 19, 2018, for trial A and May 29, 2018, for trial B.

Interventions

Intravenous administration of iron isomaltoside, 1000 mg, on day 0 or ferric carboxymaltose, 750 mg, infused on days 0 and 7.

Main Outcomes and Measures

The primary end point was the incidence of hypophosphatemia (serum phosphate level <2.0 mg/dL) between baseline and day 35.

Results

In trial A, 123 patients were randomized (mean [SD] age, 45.1 [11.0] years; 95.9% women), including 62 to iron isomaltoside and 61 to ferric carboxymaltose; 95.1% completed the trial. In trial B, 122 patients were randomized (mean [SD] age, 42.6 [12.2] years; 94.1% women), including 61 to iron isomaltoside and 61 to ferric carboxymaltose; 93.4% completed the trial. The incidence of hypophosphatemia was significantly lower following iron isomaltoside vs ferric carboxymaltose (trial A: 7.9% vs 75.0% [adjusted rate difference, -67.0% {95% CI, -77.4% to -51.5%}], P < .001; trial B: 8.1% vs 73.7% [adjusted rate difference, -65.8% {95% CI, -76.6% to -49.8%}], P < .001). Beyond hypophosphatemia and increased parathyroid hormone, the most common adverse drug reactions (No./total No.) were nausea (iron isomaltoside: 1/125; ferric carboxymaltose: 8/117) and headache (iron isomaltoside: 4/125; ferric carboxymaltose: 5/117).

Conclusions and Relevance

In 2 randomized trials of patients with iron-deficiency anemia who were intolerant of or unresponsive to oral iron, iron isomaltoside (now called ferric derisomaltose), compared with ferric carboxymaltose, resulted in lower incidence of hypophosphatemia over 35 days. However, further research is needed to determine the clinical importance of this difference.

Trial Registration

ClinicalTrials.gov Identifiers: NCT03238911 and NCT03237065.

Oral Iron Replacement Normalizes Fibroblast Growth Factor 23 in Iron-Deficient Patients With Autosomal Dominant Hypophosphatemic Rickets

Autosomal dominant hypophosphatemic rickets (ADHR) is caused by mutations impairing cleavage of fibroblast growth factor 23 (FGF23). FGF23 gene expression increases during iron deficiency. In humans and mice with the ADHR mutation, iron deficiency results in increased intact FGF23 concentrations and hypophosphatemia. We conducted a prospective open label pilot clinical trial of oral iron replacement over 12 months in ADHR patients to test the hypothesis that oral iron administration would normalize FGF23 concentrations. Eligibility criteria included: FGF23 mutation; and either serum iron <50 μg/dL; or serum iron 50 to 100 μg/dL combined with hypophosphatemia and intact FGF23 >30 pg/mL at screening. Key exclusion criteria were kidney disease and pregnancy. Oral iron supplementation started at 65 mg daily and was titrated based on fasting serum iron concentration. The primary outcome was decrease in fasting intact FGF23 by ≥20% from baseline. Six adults (three male, three female) having the FGF23-R176Q mutation were enrolled; five completed the 12-month protocol. At baseline three of five subjects had severely symptomatic hypophosphatemia (phosphorus <2.5 mg/dL) and received calcitriol with or without phosphate concurrent with oral iron during the trial. The primary outcome was met by 4 of 5 (80%) subjects all by month 4, and 5 of 5 had normal intact FGF23 at month 12. Median (minimum, maximum) intact FGF23 concentration decreased from 172 (20, 192) pg/mL at baseline to 47 (17, 78) pg/mL at month 4 and 42 (19, 63) pg/mL at month 12. Median ferritin increased from 18.6 (7.7, 82.5) ng/mL at baseline to 78.0 (49.6, 261.0) ng/mL at month 12. During iron treatment, all three subjects with baseline hypophosphatemia normalized serum phosphorus, had markedly improved symptoms, and were able to discontinue calcitriol and phosphate. Oral iron repletion normalized FGF23 and phosphorus in symptomatic, iron-deficient ADHR subjects. Thus, the standard approach to ADHR should include recognition, treatment, and prevention of iron deficiency. © 2019 American Society for Bone and Mineral Research.

Osteomalacia and Insufficiency Fractures Secondary to Intravenous Iron Therapy: A Case Report

Introduction

Intravenous (IV) iron therapy is associated with hypophosphatemia, and long-term administration may lead to osteomalacia and insufficiency fracture. Awareness of this complication could severely reduce patient morbidity. Our patient continued her iron therapy for 17 months after her initial complaint. After switching iron medications, the patient's fractures healed completely and she is now pain free.

Case Report

A 61-year-old woman presented with a fracture in her right femoral neck and a non-displaced fracture in her left femoral neck. After total hip arthroplasty and pinning, the patient returned with bilateral insufficiency fractures of the medial tibial plateau. The fractures were secondary to her iron medication, ferric carboxymaltose (FCM).

Conclusion

Fibroblast growth factor 23 (FGF23) is a protein that increases renal phosphate wasting and certain parenteral iron therapies may increase the activity of FGF23. Most IV iron medications have been shown to cause hypophosphatemia, but literature has indicated that FCM is associated with the highest risk of developing hypophosphatemia and possibly osteomalacia.

Osteocytic FGF23 and Its Kidney Function

Osteocytes, which represent up to 95% of adult skeletal cells, are deeply embedded in bone. These cells exhibit important interactive abilities with other bone cells such as osteoblasts and osteoclasts to control skeletal formation and resorption. Beyond this local role, osteocytes can also influence the function of distant organs due to the presence of their sophisticated lacunocanalicular system, which connects osteocyte dendrites directly to the vasculature. Through these networks, osteocytes sense changes in circulating metabolites and respond by producing endocrine factors to control homeostasis. One critical function of osteocytes is to respond to increased blood phosphate and 1,25(OH)₂ vitamin D (1,25D) by producing fibroblast growth factor-23 (FGF23). FGF23 acts on the kidneys through partner fibroblast growth factor receptors (FGFRs) and the co-receptor Klotho to promote phosphaturia via a downregulation of phosphate transporters, as well as the control of vitamin D metabolizing enzymes to reduce blood 1,25D. In the first part of this review, we will explore the signals involved in the positive and negative regulation of FGF23 in osteocytes. In the second portion, we will bridge bone responses with the review of current knowledge on FGF23 endocrine functions in the kidneys.

FGF23 at the crossroads of phosphate, iron economy and erythropoiesis

Fibroblast growth factor 23 (FGF23) was initially characterized as an important regulator of phosphate and calcium homeostasis. New research advances demonstrate that FGF23 is also linked to iron economy, inflammation and erythropoiesis. These advances have been fuelled, in part, by the serendipitous development of two distinct FGF23 assays that can substitute for invasive bone biopsies to infer the activity of the three main steps of FGF23 regulation in bone: transcription, post-translational modification and peptide cleavage. This 'liquid bone biopsy for FGF23 dynamics' enables large-scale longitudinal studies of FGF23 regulation that would otherwise be impossible in humans. The balance between FGF23 production, post-translational modification and cleavage is maintained or perturbed in different hereditary monogenic conditions and in acquired conditions that mimic these genetic disorders, including iron deficiency, inflammation, treatment with ferric carboxymaltose and chronic kidney disease. Looking ahead, a deeper understanding of the relationships between FGF23 regulation, iron homeostasis and erythropoiesis can be leveraged to devise novel therapeutic targets for treatment of anaemia and states of FGF23 excess, including chronic kidney disease.

Symptomatic hypophosphataemia after intravenous iron therapy: an underrated adverse reaction

Iron (ferric carboxymaltose) infusion therapy is used to treat severe iron deficiency which is not responding to the first-line oral iron therapy. However, it can also cause severe renal wasting of phosphate resulting in severe hypophosphataemia in some patients. Despite the growing number of case reports, this side effect is not well known to healthcare professionals. The product labelling information sheet does mention that hypophosphataemia can be a side effect, but also says that this side effect is usually transient and asymptomatic. We report a challenging case of a patient who developed severe, symptomatic and prolonged hypophosphataemia after an intravenous iron infusion for severe iron deficiency.

Regulation of Fibroblast Growth Factor 23 by Iron, EPO, and HIF

Purpose of review

Fibroblast growth factor-23 (FGF23) is the key hormone produced in bone critical for phosphate homeostasis. Elevated serum phosphorus and 1,25dihydroxyvitaminD stimulates FGF23 production to promote renal phosphate excretion and decrease 1,25dihydroxyvitaminD synthesis. Thus completing the feedback loop and suppressing FGF23. Unexpectedly, studies of common and rare heritable disorders of phosphate handling identified links between iron and FGF23 demonstrating novel regulation outside the phosphate pathway.

Recent Findings

Iron deficiency combined with an FGF23 cleavage mutation was found to induce the autosomal dominant hypophosphatemic rickets phenotype. Physiological responses to iron deficiency, such as erythropoietin production as well as hypoxia inducible factor activation, have been indicated in regulating FGF23. Additionally, specific iron formulations, used to treat iron deficiency, alter post-translational processing thereby shifting FGF23 protein secretion.

Summary

Molecular and clinical studies revealed that iron deficiency, through several mechanisms, alters FGF23 at the transcriptional and post-translational level. This review will focus upon the novel discoveries elucidated between iron, its regulators, and their influence on FGF23 bioactivity.

Randomized trial of intravenous iron-induced hypophosphatemia

BACKGROUND

Hypophosphatemia can complicate intravenous iron therapy, but no head-to-head trials compared the effects of newer intravenous iron formulations on risks and mediators of hypophosphatemia.

METHODS

In a randomized, double-blinded, controlled trial of adults with iron deficiency anemia from February 2016 to January 2017, we compared rates of hypophosphatemia in response to a single FDA-approved course of ferric carboxymaltose (n = 1,000) or ferumoxytol (n = 997). To investigate pathophysiological mediators of intravenous iron-induced hypophosphatemia, we nested within the parent trial a physiological substudy (ferric carboxymaltose, n = 98; ferumoxytol, n = 87) in which we measured fibroblast growth factor 23 (FGF23), calcitriol, and parathyroid hormone (PTH) at baseline and 1, 2, and 5 weeks later.

RESULTS

The incidence of hypophosphatemia was significantly higher in the ferric carboxymaltose versus the ferumoxytol group (<2.0 mg/dl, 50.8% vs. 0.9%; <1.3 mg/dl, 10.0% vs. 0.0%; P < 0.001), and hypophosphatemia persisted through the end of the 5-week study period in 29.1% of ferric carboxymaltose-treated patients versus none of the ferumoxytol-treated patients (P < 0.001). Ferric carboxymaltose, but not ferumoxytol, increased circulating concentrations of biologically active FGF23 (mean within-patient percentage change from baseline to week 2 peak: +302.8 ± 326.2% vs. +10.1 ± 61.0%; P < 0.001), which was significantly associated with contemporaneous hypophosphatemia, renal phosphate wasting, and decreased serum calcitriol and calcium, and increased PTH concentrations.

CONCLUSIONS

Ferric carboxymaltose rapidly increases biologically active FGF23 in patients with iron deficiency anemia. Paralleling hereditary and other acquired syndromes of hypophosphatemic rickets/osteomalacia, ferric carboxymaltose-induced FGF23 elevation triggers a pathophysiological cascade of renal phosphate wasting, calcitriol deficiency, and secondary hyperparathyroidism that frequently culminates in hypophosphatemia.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02694978FUNDING. AMAG Pharmaceuticals, Inc.Role of the funding source: This study was supported by AMAG Pharmaceuticals, Inc. The academic investigators designed the clinical trial, performed the analyses, and authored the manuscript with input from the coauthors from AMAG Pharmaceuticals, Inc.

Mineral and Bone Disorders After Kidney Transplantation

The risk of mineral and bone disorders among patients with chronic kidney disease is substantially elevated, owing largely to alterations in calcium, phosphorus, vitamin D, parathyroid hormone, and fibroblast growth factor 23. The interwoven relationship among these minerals and hormones results in maladaptive responses that are differentially affected by the process of kidney transplantation. Interpretation of conventional labs, imaging, and other fracture risk assessment tools are not standardized in the post-transplant setting. Post-transplant bone disease is not uniformly improved and considerable variation exists in monitoring and treatment practices. A spectrum of abnormalities such as hypophosphatemia, hypercalcemia, hyperparathyroidism, osteomalacia, osteopenia, and osteoporosis are commonly encountered in the post-transplant period. Thus, reducing fracture risk and other bone-related complications requires recognition of these abnormalities along with the risk incurred by concomitant immunosuppression use. As kidney transplant recipients continue to age, the drivers of bone disease vary throughout the post-transplant period among persistent hyperparathyroidism, de novo hyperparathyroidism, and osteoporosis. The use of anti-resorptive therapies require understanding of different options and the clinical scenarios that warrant their use. With limited studies underscoring clinical events such as fractures, expert understanding of MBD physiology, and surrogate marker interpretation is needed to determine ideal and individualized therapy.