Iron Infusion and Induced Hypophosphatemia: The Role of Fibroblast Growth Factor-23

Concurrent Denosumab and Parenteral Iron Therapy Precipitating Severe Hypocalcemia and Hypophosphatemia

Denosumab-induced hypocalcemia and iron infusion-related hypophosphatemia are both well described. We describe a case of severe hypocalcemia and hypophosphatemia following sequential denosumab and parenteral iron administration. This resulted in respiratory failure due to muscle weakness and cardiac arrhythmia, requiring noninvasive ventilation and urgent intravenous electrolyte replacement. This case highlights the severe dysregulation in calcium and phosphate homeostasis that can occur with denosumab and iron infusions when administered in quick succession. Given that these drugs are among the most common therapies prescribed across a range of specialties, we hope to alert clinicians to this potential serious drug-drug interaction and suggest strategies for monitoring and management of the electrolyte derangement.

Mineral Bone Disorders in Kidney Disease Patients: The Ever-Current Topic

Chronic kidney disease (CKD) is a complex and multifactorial disease, and one of the most prevalent worldwide. Chronic kidney disease–mineral bone disorders (CKD–MBD) with biochemical and hormonal alterations are part of the complications associated with the progression of CKD. Pathophysiology of CKD–MBD focused on abnormalities in serum levels of several biomarkers (such as FGF-23, klotho, phosphate, calcium, vitamin D, and PTH) which are discussed in this review. We therefore examine the prognostic association between CKD–MBD and the increased risk for cardiovascular events, mortality, and CKD progression to end-stage kidney disease (ESKD). Lastly, we present specific treatments acting on CKD to prevent and treat the complications associated with secondary hyperparathyroidism (SHPT): control of hyperphosphatemia (with dietary restriction, intestinal phosphate binders, and adequate dialysis), the use of calcimimetic agents, vitamin D, and analogues, and the use of bisphosphonates or denosumab in patients with osteoporosis.

Severe Hypophosphatemia Occurring After Repeated Exposure to a Parenteral Iron Formulation

Hypophosphatemia is a less known complication of parenteral iron use, particularly after the use of certain iron formulations. We report the case of a young male with inflammatory bowel disease and iron deficiency anemia, who developed severe symptomatic hypophosphatemia after his third exposure to iron carboxymaltose with no evidence of the same occurring upon prior exposures to the compound. Investigations revealed serum phosphorous levels of 0.7 mg/dl, corrected serum calcium of 8-9.5 mg/dl, alkaline phosphatase of 50 U/L (38-126), 25 hydroxy vitamin D level of 40.2 ng/ml, and intact PTH elevated to 207 pg/ml. Urine studies indicated renal phosphate wasting. Presentation was not in keeping with refeeding syndrome. Intact fibroblast growth factor 23 level, measured after the initiation of treatment was within the normal range at 179 RU/mL (44-215). 1,25 dihydroxy vitamin D level, also measured after the initiation of treatment, was normal at 26.3 pg/ml (19.9-79.3). The patient was treated with calcitriol and aggressive oral and intravenous phosphorous repletion. Symptoms then resolved and the patient was discharged on an oral regimen. This phenomenon is postulated to occur due to an increase in the level and activity of FGF23 and decreased cleavage of the same, due to anemia as well as use of specific iron formulations. This is the first instance, in our literature review, of this complication known to occur, not after initial exposure to an implicated iron formulation but occurring on subsequent exposure.

Refractory hypophosphatemia following ferric carboxymaltose administration

Hypophosphatemia is a rare side effect of intravenous iron replacement. Urinary phosphate wasting due to increased FGF23 is the most likely mechanism. Here, we present a case of intractable hypophosphatemia in a 32-year-old female patient with history of ulcerative colitis (UC), who was primarily hospitalized due to UC flare-up. Her urinary fractional excretion of phosphate was inappropriately elevated at 70%. A careful history revealed that she had been treated with ferric carboxymaltose 2 weeks prior to hospitalization, leading to a diagnosis of iron-induced hypophosphatemia. She was treated with 5 weeks of intravenous sodium phosphate since she did not tolerate oral supplementation. In conclusion, clinicians should be aware of iron-induced hypophosphatemia and be cautious when prescribing intravenous iron.

British Intestinal Failure Alliance (BIFA) guidance - haematological and biochemical monitoring of adult patients receiving home parenteral nutrition

Home parenteral nutrition (HPN) is necessary for patients with prolonged intestinal failure which can be secondary to a variety of pathophysiological mechanisms or surgical resection. HPN is needed to supply micronutrients, macronutrients and water to reduce morbidity and mortality and to maximise the patient's quality of life. HPN requires close monitoring by a dedicated multidisciplinary team and is vital to minimise complications; both catheter related and metabolic. A regular comprehensive review is required including history, examination including anthropometry and blood testing. The focus of this review is on the monitoring of haematological and biochemical parameters. There is a paucity of evidence-based literature on the biochemical monitoring of HPN and existing guidance is sourced mostly on expert opinion and lower grade studies. Sources offering guidance on the frequency of biochemical monitoring for the stable adult HPN patient are the British Association for Parenteral and Enteral Nutrition, the European Society for Parenteral and Enteral Nutrition, the National Institute for Health and Care Excellence and the Australasian Society of Parenteral and Enteral Nutrition (AuSPEN). The aim of this work is to review and collate this existing guidance into one clear and concise review. It is recommended that biochemical parameters are checked at baseline, thereafter more frequently if concerns arise and less frequently when the patient's condition is stable, as assessed by the multidisciplinary team with expertise in HPN.

Klotho, Aging, and the Failing Kidney

Klotho has been recognized as a gene involved in the aging process in mammals for over 30 years, where it regulates phosphate homeostasis and the activity of members of the fibroblast growth factor (FGF) family. The α-Klotho protein is the receptor for Fibroblast Growth Factor-23 (FGF23), regulating phosphate homeostasis and vitamin D metabolism. Phosphate toxicity is a hallmark of mammalian aging and correlates with diminution of Klotho levels with increasing age. As such, modulation of Klotho activity is an attractive target for therapeutic intervention in the diseasome of aging; in particular for chronic kidney disease (CKD), where Klotho has been implicated directly in the pathophysiology. A range of senotherapeutic strategies have been developed to directly or indirectly influence Klotho expression, with varying degrees of success. These include administration of exogenous Klotho, synthetic and natural Klotho agonists and indirect approaches, via modulation of the foodome and the gut microbiota. All these approaches have significant potential to mitigate loss of physiological function and resilience accompanying old age and to improve outcomes within the diseasome of aging.

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.