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.

Incidence of hypophosphatemia in patients with inflammatory bowel disease treated with ferric carboxymaltose or iron isomaltoside.

BACKGROUND: Iron deficiency and iron deficiency anaemia are common complications in inflammatory bowel disease (IBD). In patients with moderate-to-severe anaemia, oral iron intolerance or ineffectiveness of oral iron, ferric carboxymaltose and iron isomaltoside are widely used. Hypophosphatemia is a side effect of both preparations. AIMS: To investigate the occurrence of hypophosphatemia in IBD patients with iron deficiency/iron deficiency anaemia treated with high-dose intravenous iron. METHODS: A prospective observational study of adult IBD patients with iron deficiency/iron deficiency anaemia was conducted at two study sites where patients received 1000 mg of ferric carboxymaltose or iron isomaltoside. At baseline, weeks 2 and 6, blood and faecal samples were collected. The primary endpoint was to determine the incidence of moderate-to-severe hypophosphatemia. Secondary endpoints included the total incidence of hypophosphatemia, possible risk factors for hypophosphatemia, and response to single-dose intravenous iron. RESULTS: One hundred and thirty patients were included. In the per-protocol set, 52 patients received ferric carboxymaltose and 54 patients received iron isomaltoside. Ferric carboxymaltose treatment had a significantly higher incidence of moderate-to-severe hypophosphatemia compared with iron isomaltoside at week 2 (56.9% vs 5.7%, P < 0.001) and a higher incidence at week 6 (13.7% vs 1.9%, P = 0.054).The overall incidence of hypophosphatemia was significantly higher with ferric carboxymaltose compared with iron isomaltoside treatment at weeks 2 (72.5% vs 11.3%, P < 0.001) and 6 (21.6% vs 3.7%, P = 0.013). CONCLUSIONS: In IBD patients with iron deficiency/iron deficiency anaemia, ferric carboxymaltose was associated with higher incidence, severity and persistence of hypophosphatemia compared with iron isomaltoside. The presence of moderate-to-severe hypophosphatemia beyond 6 weeks is a clinical concern that requires further investigation.