A prespecified substudy of the HEART-FID trial has found that ferric carboxymaltose (FCM), a recommended therapy for iron deficiency (ID) in heart failure with reduced ejection fraction (HFrEF), frequently induces moderate to severe hypophosphatemia. However, the condition appears to be transient, clinically benign, and not associated with adverse events.

The study, published in European Journal of Heart Failure, analyzed 133 ambulatory HFrEF patients with ID who were randomized to receive either FCM (n = 62) or placebo (n = 71) and followed over eight visits spanning six months. The mean age of participants was 68 years, 41.4% were women, and 21.8% had chronic kidney disease. Researchers assessed changes in serum phosphate, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and parathyroid hormone (PTH) levels.

Phosphate reductions were observed in 57.6% of the FCM group compared with only 10.3% in the placebo group. The lowest phosphate levels were recorded at day 21 following FCM infusion, with a mean drop of −0.36 mmol/L; 51% of treated patients experienced moderate to severe hypophosphatemia. Concurrent reductions in 1,25-dihydroxyvitamin D and increases in PTH were noted, while 25-hydroxyvitamin D levels remained stable throughout. These changes were resolved by day 91. There were no serious or symptomatic adverse events associated with hypophosphataemia.