Background: Ferric carboxymaltose (FCM) can induce hypophosphataemia in the general population and patients with chronic kidney disease (CKD). Less is known about the effect of FCM in the kidney transplant population. It has been suggested that fibroblast growth factor 23 (FGF-23)-mediated renal phosphate wasting may be the most likely cause of this phenomenon. In the current study, the effects of FCM on phosphate metabolism were studied in a cohort of kidney transplant recipients.
Methods: Two index patients receiving FCM are described. Additionally, data of 23 kidney transplant recipients who received a single dose of FCM intravenously between 1 January 2014 and 1 July 2015 were collected. Changes in the serum phosphate concentration were analysed in all subjects. Change in plasma FGF-23 concentrations was analysed in the index patients.
Results: In the two index patients an increase in FGF-23 and a decrease in phosphate concentrations were observed after FCM administration. In the 23 kidney transplant patients, median estimated glomerular filtration rate was 42 ml/min/1.73 m2 ( range 10-90 ml/ min/1.73 m2). Mean phosphate concentration before and after FCM administration was 1.05 ± 0.35 mmol/l and 0.78 ± 0.41 mmol/l, respectively (average decrease of 0.27 mmol/l; p = 0.003). In the total population, 13 (56.5%) patients showed a transient decline in phosphate concentration after FCM administration. Hypophosphataemia following FCM administration was severe (i.e. < 0.5 mmol/l) in 8 (34.8%) patients.
Conclusion: Administration of a single dose of FCM may induce transient and mostly asymptomatic renal phosphate wasting and hypophosphataemia in kidney transplant recipients. This appears to be explained by an increase in FGF-23 concentration.