Iron deficiency anemia in the perioperative setting is treated predominantly with intravenous iron formulation, of which ferric carboxymaltose may induce hypophosphatemia by modulating fibroblast growth factor 23. In this single-center, prospective, randomized, double-blind trial, we consented 92 adult patients scheduled for elective major abdominal or thoracic surgery. These patients either had isolated iron deficiency (plasma ferritin <100ng/mL or transferrin saturation<20%) or iron deficiency anemia (hemoglobin (Hb) 100-130g/L with plasma ferritin <100ng/mL or transferrin saturation<20%). Preoperatively, participants received a single preoperative intravenous dose of ferric carboxymaltose and were then randomly assigned to receive either phosphate or placebo, administered orally three times a day for 30days corresponding to an 18mmol dose of daily phosphate supplementation in the intervention group. The primary endpoint was the minimum serum phosphate concentration during follow-up visits. The key secondary efficacy endpoint was mean perioperative hemoglobin concentration of postoperative days 0, 2 and 4, assessing the non-inferiority of additional phosphate supplementation. We randomly consented 46 patients in each group (mean±SD age 56±17years, 57% female). Minimal phosphate concentration was 0.49±0.21mmol/L in the treatment group and 0.42±0.17mmol/L in the placebo group (p=0.12, two-sided p-value). Average mean hemoglobin was 110±16g/L in the treatment and 113±13g/L in the placebo group (p=0.023, one-sided p-value for non-inferiority). Hypophosphatemia occurred in 32 patients (70%) of the treatment group and in 39 patients (85%) of the placebo group (odds ratio 0.15, 95% CI from 0.02 to 0.77, p=0.014). Secondary outcomes, such as rescue medication use, core muscle strength and MOCA test scores, did not differ between groups. Co-administration of oral phosphate supplementation to ferric carboxymaltose cannot prevent hypophosphatemia. However, hypophosphatemia occurs in fewer patients. Phosphate co-administration did not impede the treatment of iron deficiency anemia with ferric carboxymaltose.
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