FDA Adds a Boxed Warning to Injectafer for Low Phosphate Levels. Check How Your Infusion Protocols Handle It.
FDA's Sept. 1 Drug Safety Communication says serum phosphate was measured in fewer than 20 percent of ferric carboxymaltose administration episodes. The new boxed warning calls for a check before any repeat course within three months.
On Sept. 1, the Food and Drug Administration published a Drug Safety Communication announcing that it had approved a boxed warning for ferric carboxymaltose injection (Injectafer, American Regent) describing the risk of symptomatic hypophosphatemia. The warning is the agency's most prominent, and it recommends phosphate monitoring in patients at risk and in anyone who receives a repeat course within three months.
Hypophosphatemia was already in the label. What changed is its placement and the evidence behind it: FDA says monitoring has lagged well behind what earlier warnings recommended.
What changed
FDA's communication traces the history. The agency determined in 2019 that the drug can cause serious symptomatic hypophosphatemia, added a warning in February 2020, and added serum phosphate monitoring recommendations in 2023. A 2025 revision added risk factors. The current Injectafer label on DailyMed lists the boxed warning and the revised Warnings and Precautions section as August 2026 changes. The Sept. 1 communication is FDA's notice to clinicians.
The advocacy group Cure HHT reported that FDA granted a citizen petition from Scott Olitsky, MD, its Global Center of Excellence and Outreach Director, on Aug. 13, and tied the boxed warning to that petition. FDA's communication does not mention the petition.
What FDA found
FDA reviewed its adverse event database, published literature and the Sentinel System. It found that symptomatic hypophosphatemia continues to be reported after both single and multiple infusions. Consequences included hospitalization, phosphate replacement over weeks to months, and extensive follow-up monitoring.
The testing figure is the one to note. Sentinel data indicate that serum phosphate was measured in fewer than 20 percent of ferric carboxymaltose administration episodes.
A boxed warning does not change who can receive Injectafer. It raises the cost of not checking phosphate.
What the label says to do
The boxed warning states that Injectafer can cause severe, prolonged hypophosphatemia with serious outcomes, including hospitalization, osteomalacia and fractures requiring clinical intervention. It also states that hypophosphatemia has occurred in patients with normal baseline phosphate levels, and the label notes cases in patients without apparent risk factors, so a clean risk profile does not rule it out.
The label directs prescribers to check serum phosphate before a repeat course in patients at risk and in anyone treated again within three months, and to correct existing hypophosphatemia before dosing. It asks prescribers to monitor patients at risk for chronic low phosphate, to treat hypophosphatemia as medically indicated, and to consider permanent discontinuation for severe symptomatic or persistent cases. In most reported cases, the label says, hypophosphatemia resolved within three months.
Listed risk factors include gastrointestinal disorders associated with malabsorption of fat-soluble vitamins or phosphate, inflammatory bowel disease, concurrent or prior use of drugs that affect proximal renal tubular function, hyperparathyroidism, vitamin D deficiency, malnutrition and hereditary hemorrhagic telangiectasia. FDA also notes that some symptoms can mimic those of iron deficiency anemia, which complicates bedside recognition.
The label's trial data show how common the laboratory finding is. Transient phosphorus values below 2 mg/dL occurred in 27 percent (440 of 1,638) of patients in clinical trials. That figure describes lab values, not symptomatic disease, and FDA's postmarketing reports cannot supply an incidence rate.
What practices should do now
For patients weighing 50 kg or more, the labeled regimen is 750 mg in two doses at least seven days apart, or for adults a single dose of 15 mg/kg up to 1,000 mg. The three-month rule matters for any patient who needs another course soon after the first. Hematology, gastroenterology, nephrology, cardiology, obstetrics and gynecology, and infusion-center teams should check four points in their protocols.
First, whether a phosphate order is built into the repeat-course pathway and who reviews the result. Second, whether the diagnoses on the label's risk list are flagged at scheduling. Third, whether patients are told which symptoms to report, such as fatigue, muscle weakness, or bone and joint pain, and whom to call. Fourth, whether the drug on the shelf is the brand or a generic: FDA says generic ferric carboxymaltose labeling is expected to be updated, so labels may lag.
The communication addresses ferric carboxymaltose only. It does not rank other IV iron products or say when to switch, and that choice remains a clinical judgment. Suspected cases can be reported through FDA's MedWatch program.
Reported, fact-checked and edited by The Script Pad's editorial staff.
This article is for professional education and does not replace clinical judgment. Treatment decisions should be based on the individual patient and current guidelines.
