Trends of phosphorus levels after intravenous administration of ferric carboxymaltose

Abstract Background Iron deficiency and anaemia are present in a large number of patients with heart failure. Intravenously ferric carboxymaltose (FCM) is the recommended treatment, but it may be associated with hypersensitivity reaction and hypophosphatemia, the later mainly in subjects with normal renal function. The prevalence of hypophosphatemia driven by FCM in patients with heart failure (HF) is not well established. Purpose To assess the prevalence and trends of serum phosphorus levels after FCM administration in outpatients with HF. Methods Prospective, observational, consecutive, and descriptive study of patients admitted in a HF clinic eligible to receive FCM between January 2022 and June 2022. Phosphorus and calcium homeostasis regulators (magnesium, vitamin D, parathyroid hormone, alkaline phosphatase) were drawn at baseline and after 3 weeks of the infusion. In those patients with documented hypophosphatemia after iron administration, a third measurement was performed at three months from baseline. Paired T-test was used to compare mean values and logistic regression to predict relationship of changes in serum phosphorus with other factors. Results 101 patients were included (71.5 ± 10.6 years, 31.7% women, LVEF 43.9 ±11.9%, 49.5% of ischaemic aetiology, glomerular filtration rate 39.44 ±10 mL/min/m2). Mean baseline phosphorous was 3.64 ± 0.66 mg/dL, declining to 2.74 ±0.88 mg/dL (p for trend = 0.001). Calcium, magnesium, and vitamin D also showed a post-infusion declining tendency (p = 0.001, p = 0.05 and p= 0.002, respectively), whereas PTH significantly increased (p = 0.015). At three weeks, 38 (37.6%) patients had phosphorous levels below the normal threshold (mean 2.15 ± 0.76 mg/dl), which normalized at three months from baseline (mean 3.12 ±0.77 mg/dl; p = 0.71) without specific treatment. Figure 1 shows phosphorus dynamics of the 38 patients with infusion hypophosphatemia. There was no predicted correlation between FCM dose, glomerular filtration rate and phosphorous trends (p = 0.627, P = 0.234 respectively). No clinical adverse event was reported. Conclusion Ferric carboxymaltose infusion in patients with HF is associated with a decline in circulating phosphorous, with 1 in 3 patients showing frank hypophosphatemia. This effect is transient and does not require treatment nor active phosphorus monitoring.Trends of hypophosphatemia