IV iron regimens compared for serum phosphate effects in patients with IBD

Ferric carboxymaltose and ferric derisomaltose worked well to resolve anemia from inflammatory bowel disease (IBD), but the former was associated with low serum phosphate levels, according to an industry-funded trial.

Ferric carboxymaltose (FCM) was associated with a significantly higher rate of hypophosphatemia than ferric derisomaltose (FDI) in patients with iron deficiency anemia due to inflammatory bowel disease (IBD), although both drugs were comparably effective, a recent trial found.

Researchers conducted the randomized, double-blind clinical trial at 20 outpatient hospital clinics in Austria, Denmark, Germany, Sweden, and the United Kingdom. Adults with IBD and iron deficiency anemia were randomized 1:1 to receive intravenous FCM or FDI at baseline and at day 35. The goal of the study was to make a head-to-head comparison of the risk of hypophosphatemia after equivalent dosing. Pharmacosmos A/S funded and sponsored the trial and was involved in most aspects of its conduct, including data collection/analysis and manuscript review. The trial's primary outcome was the incidence of hypophosphatemia, defined as a serum phosphate level below 2.0 mg/dL, at any time from baseline to day 35. The researchers also measured markers of mineral and bone homeostasis and patient-reported fatigue scores. Results of the trial were published Sept. 9 by Gut.

Ninety-seven patients were assigned to treatment, 49 to FDI and 48 to FCM. Hypophosphatemia occurred in 8.3% of the former group versus 51.0% of the latter (adjusted risk difference, −42.8% [95% CI, –57.1% to –24.6%]; P<0.0001). Both iron formulations were effective in correcting anemia. Patient-reported fatigue scores improved in both groups but more slowly and not as much with FCM versus FDI. Compared with FDI, hypophosphatemia after FCM was associated with more pronounced increases in intact fibroblast growth factor 23 (FGF23) level, renal phosphate excretion, and parathyroid hormone level and more pronounced decreases in levels of 1,25-dihydroxyvitamin D.

The authors noted the short duration of the trial and the need for future studies to investigate longer-term clinical consequences of hypophosphatemia and the mechanisms responsible for the differential effects of FCM and FDI on patient-reported fatigue.

“[H]ypophosphataemia is not a class or dose effect of intravenous iron, but a particularly common adverse effect of FCM that is driven by marked increases in FGF23,” the authors wrote. “Despite equivalent dosing schedules, the effects of FDI on FGF23 and, thus, serum phosphate are much smaller. This study shows that hypophosphataemia is a common complication of FCM use in patients with IBD.”