The FDA has added a boxed warning to the labeling for ferric carboxymaltose injection (Injectafer), citing the risk of symptomatic hypophosphatemia. It’s the agency’s strongest safety warning, and it arrives after two earlier attempts to address the same risk through ordinary labeling changes.
Why now
The warning about low phosphate isn’t new. The FDA added it in February 2020 and expanded it in May 2023 to include phosphate monitoring recommendations, additional risk factors and long-term skeletal complications.
What changed is the evidence that those measures weren’t working. A 2026 FDA review of postmarketing reports, published literature and real-world safety data, found that symptomatic hypophosphatemia continues to occur, and that phosphate monitoring remains underutilized in practice.
That last finding is the reason a boxed warning was the next step. The clinical guidance had been available for six years. The behavior it was meant to change hadn’t changed enough.
What the warning covers
Symptomatic hypophosphatemia can result in muscle weakness, fatigue, confusion, seizures and cardiac arrhythmias. In prolonged severe cases it can lead to osteomalacia and fractures.
The complicating factor is overlap. Muscle weakness and fatigue are also symptoms of the iron deficiency anemia that ferric carboxymaltose is given to treat. A patient reporting that they still feel weak after an infusion may be describing incomplete response, or may be describing a new problem the infusion caused. Without a phosphate level, there is no way to tell the difference.
Updated monitoring recommendations
The revised labeling recommends monitoring serum phosphate levels in:
- Patients at risk for hypophosphatemia
- Patients receiving a repeat treatment course within three months
Pharmacy required action
Counsel patients on symptom reporting. Advise patients to immediately report any new or worsening symptoms of low phosphate levels, including muscle weakness or pain, fatigue, bone and joint pain, and confusion. Make the overlap explicit when you counsel. Patients who assume weakness is simply their anemia will not call.
Reassess the risk-benefit balance. Determine whether the potential benefits of continuing the drug outweigh the risks described in this communication, and make sure prescribers are informing patients of the hypophosphatemia risk associated with ferric carboxymaltose.
Product information
Reporting adverse events
Report adverse events related to this or any other drug product to MedWatch, the FDA Safety Information and Adverse Event Reporting Program:
- Complete and submit the MedWatch Online Voluntary Reporting Form online
- Download FDA Form 3500, or call 1-800-332-1088 to request a reporting form, then complete and return it to the address on the pre-addressed form or submit by fax to 1-800-FDA-0178
Reference
U.S. Food and Drug Administration. (2026). FDA Adds Boxed Warning to Labeling for Ferric Carboxymaltose Injection (Injectafer) to Describe Risk of Low Phosphate Levels (Hypophosphatemia). https://www.fda.gov/drugs/drug-safety-communications/fda-adds-boxed-warning-labeling-ferric-carboxymaltose-injection-injectafer-describe-risk-low
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