OBJECTIVES:

Intravenous iron (IVI) is indicated for iron deficiency and iron deficiency anemia (IDA). Important differences exist between different types of IVI, e.g. in terms of maximum single dosing and safety profiles. Certain IVI formulations have been reported to have comparable increased risk of hypophosphatemia in clinical trials, including saccharated ferric oxide (SFO) and ferric carboxymaltose (FCM). Hypophosphatemia can result in osteomalacia. We aimed to estimate hypophosphatemia prevalence, by dose, after SFO and FCM exposure in Japan.

METHODS:

This retrospective study used data from the RWD Japanese claims and health record database which is maintained by the Health, Clinic, and Education Information Evaluation Institute (Kyoto, Japan). The study population comprised all patients with a record of IDA from January 1, 2016, to December 31, 2020. Records of phosphate levels within 90 days of the first IVI dose were identified for the subgroup who received SFO or FCM. The prevalence of hypophosphatemia was estimated by IVI dose. If >1 phosphate measurements were identified, the lowest value after the first IVI dose was included in the study.

RESULTS:

Of 170,667 patients with IDA, 26,294 received either IVI (26,160 SFO, 63 FCM), 5,867 of whom had a phosphate measurement taken within 90 days of IVI infusion. After a total cumulative dose of <160 mg IVI, 11.1% had moderate hypophosphatemia (≥1mg/dL to <2mg/dL) and 0.5% had severe hypophosphatemia (<1mg/dL). This increased to 24.9% with moderate hypophosphatemia and 3.6% with severe hypophosphatemia after ≧2000 mg cumulative IVI.

CONCLUSIONS:

This study showed that hypophosphatemia is common after SFO or FCM exposure and that the risk increases with higher cumulative dose. As only 1/5 of patients had a phosphate measurement within 90 days from IVI infusion, hypophosphatemia is probably underdiagnosed. Further studies are warranted to investigate the clinical manifestations of hypophosphatemia in a real-world setting.