• Benedikt Schaefer, Philipp Würtinger, Armin Finkenstedt, Vickie Braithwaite, André Viveiros, Maria Effenberger, Irene Sulzbacher, Alexander Moschen, Andrea Griesmacher, Herbert Tilg, Wolfgang Vogel, and Heinz Zoller.
• Medical University of Innsbruck, Department of Medicine II, Gastroenterology and Hepatology, Anichstr. Innsbruck, Austria.
• Plos One. 2016 Jan 1; 11 (12): e0167146.

BackgroundFerric carboxymaltose (FCM) and iron isomaltoside 1000 (IIM) are increasingly used because they allow correction of severe iron deficiency in a single infusion. A transient decrease in serum phosphate concentrations is a frequent side effect of FCM.AimTo characterize this adverse event and search for its predictors in a gastroenterology clinic patient cohort.MethodsElectronic medical records of patients attending the University Hospital of Innsbruck were searched for the keywords ferric carboxymaltose or iron isomaltoside. Eighty-one patients with documented administration of FCM or IIM with plasma phosphate concentrations before and after treatment were included.ResultsThe prevalence of hypophosphatemia (<0.8 mmol/L) increased from 11% to 32.1% after treatment with i.v. iron. The hypophosphatemia risk was greater after FCM (45.5%) compared with IIM (4%). Severe hypophosphatemia (<0.6 mmol/L) occurred exclusively after FCM (32.7%). The odds for hypophosphatemia after i.v. iron treatment were independently determined by baseline phosphate and the choice of i.v. iron preparation (FCM vs. IIM-OR = 20.8; 95% CI, 2.6-166; p = 0.004). The median time with hypophosphatemia was 41 days, but prolonged hypophosphatemia of ≥ 2 months was documented in 13 of 17 patients in whom follow-up was available. A significant increase in the phosphaturic hormone intact FGF-23 in hypophosphatemic patients shows that this adverse event is caused by FCM-induced hormone dysregulation.ConclusionTreatment with FCM is associated with a high risk of developing severe and prolonged hypophosphatemia and should therefore be monitored. Hypophosphatemia risk appears to be substantially lower with IIM.

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