Orlando, Florida—According to data being presented at the 2019 ASH Annual Meeting, patients with iron deficiency anemia should be monitored for serum phosphate after being treated with ferric carboxymaltose.

“Over the last decade it has become apparent that hypophosphatemia may occur following some IV iron formulations. While initially considered a transient benign laboratory finding, a growing number of case reports have described treatment-emergent hypophosphatemia following IV iron administration as a safety consideration, especially in patients with normal renal function,” explained Ralph V. Boccia, MD, Center for Cancer and Blood Disorders, Bethesda, Maryland.

“Although hypophosphatemia may have clinical consequences, its diagnosis may be missed in the clinic due to initial nonspecific symptomatic presentation e.g., generalized weakness and fatigue,” they continued.

Thus, to assess the effects of IV iron on hypophosphatemia occurrence in a subgroup of participants in a double-blind, phase 3 study comparing 2 IV iron preparations for the treatment of iron deficiency anemia (IDA).

Patients in the study were randomized in a 1:1 ratio to receive two 510-mg doses of ferumoxytol or two 750-mg doses of ferric carboxymaltose delivered as an IV infusion for 15 or more minutes on days 1 and 8.

The investigators measured serum phosphate and other clinical laboratory values at baseline and on days 8, 15, and 35, and gathered data for post-hoc analyses specifically from patients with a recent or coincident cancer diagnosis.

Of 1997 patients randomized in the study, 153 had cancer (mean age 65.5 ± 13.2 years). All patients with cancer had baseline serum phosphate levels ≥2.4 mg/dL, and mean values were similar between treatment arms (ferric carboxymaltose, 3.74 ± 0.53 mg/dL and ferumoxytol, 3.86 ± 0.81 mg/dL).

Recipients of ferric carboxymaltose had significant decreases in mean serum phosphate level at each time-point compared with baseline and the ferumoxytol arm (P <.0001), whose mean phosphate did not change.

Furthermore, those given ferric carboxymaltose had a higher rate of treatment-emergent severe hypophosphatemia (<2 mg/dL) than the ferumoxytol arm, both overall (46.1% vs 1.4%, respectively; P <.0001) and at each time point (P <.001). This value peaked at week 2 and remained at 22.4% for ferric carboxymaltose at week 5.

“[M]ean serum phosphate decreased significantly in anemic cancer patients following FCM [ferric carboxymaltose], but not FER [ferumoxytol], starting as soon as 8 days following the first 750mg dose, and did not return to baseline level by the end of the study period. This resulted in hypophosphatemia <2 mg/dL that remained unresolved in some FCM patients through the end of the 5-week study,” Dr Boccia et al said.

“While this study was not designed to assess the occurrence of symptomatic hypophosphatemia, the persistence of severe hypophosphatemia among FCM [ferric carboxymaltose] patients at the end of the 5-week study period suggests the need for monitoring serum phosphate following FCM usage in clinical practice,” they concluded.—Hina Porcelli

Boccia RV, Dahl NV, Strauss WE. Severe Hypophosphatemia in Patients with Cancer Following IV Iron Treatment: Results from a Large Comparative Trial. Presented at: the 2019 ASH Annual Meeting & Exposition; December 7-10, 2019; Orlando, FL. Abstract 2236.