The Food and Drug Administration has placed its most prominent safety warning on ferric carboxymaltose, sold in the United States as Injectafer, an intravenous iron treatment given in outpatient infusion suites, hematology clinics and hospital day units across the country. The agency’s September 1 drug safety communication adds a boxed warning describing the risk of symptomatic hypophosphatemia, dangerously low blood phosphate, and comes after regulators found that a recommended monitoring blood test is skipped in the vast majority of infusions. The drug remains approved and on the market; the change concerns warnings and monitoring, not a recall.
A Citizen Petition That Reached the FDA’s Highest Warning Tier
The boxed warning followed a citizen petition from Scott Olitsky, who directs Cure HHT’s Global Center of Excellence and Outreach Program, an advocacy and research organization for hereditary hemorrhagic telangiectasia, a rare bleeding disorder whose patients often need repeated iron infusions. On August 13, the FDA granted his petition calling for stronger safety language on ferric carboxymaltose, citing continued reports of hypophosphatemia despite earlier label updates. A boxed warning, sometimes called a black-box warning, is the strongest labeling requirement the agency can impose short of removing a product from the market.
Seven Years of Escalating Language on the Same Risk
This is not the FDA’s first move on the issue. The agency determined in 2019 that ferric carboxymaltose could cause serious symptomatic hypophosphatemia, and a warning was added to the label in February 2020. That warning was revised in May 2023 to add phosphate-monitoring recommendations, to name osteomalacia and fractures as possible long-term complications, and to list inflammatory bowel disease as a risk factor. It was revised again in 2025 to add further risk factors. The label’s Warnings and Precautions section, most recently revised in January 2025, already instructed clinicians to check serum phosphate in patients at risk of low levels before a repeat course of treatment. The boxed warning elevates that same guidance to the label’s most visible position rather than introducing a new recommendation.
What Sentinel System Data Revealed About Monitoring
The most striking figure behind the decision is not about the drug’s side effects but about how often clinicians check for them. Data from the FDA’s Sentinel System, which tracks real-world use of approved drugs, show that serum phosphate testing occurs in fewer than 20 percent of ferric carboxymaltose administration episodes. Reviewing adverse-event reports and published literature, the agency identified 134 cases of serious, symptomatic hypophosphatemia between July 1, 2022, and June 30, 2025, some of which were severe, prolonged or difficult to treat. In earlier clinical trials submitted for approval, transient drops in blood phosphorus below 2 milligrams per deciliter were recorded in 27 percent of treated patients, illustrating how common low readings are even when they do not become symptomatic.
Who Carries the Highest Risk of Low Phosphate
Risk is concentrated in patients who receive repeat infusions, particularly a second course within three months of the first, and in those with underlying conditions that predispose them to phosphate loss. The label lists gastrointestinal disorders involving malabsorption, inflammatory bowel disease, hyperparathyroidism, vitamin D deficiency, malnutrition and hereditary hemorrhagic telangiectasia as possible risk factors. Injectafer is approved for iron deficiency anemia in patients as young as one year old who cannot tolerate or do not respond to oral iron, for adults with non-dialysis-dependent chronic kidney disease, and for adults with heart failure classified as New York Heart Association class II or III. Because the product is approved down to age one, the new labeling applies to pediatric patients as well as adults.
A Diagnosis That Can Hide Behind the Condition It Treats
Clinicians face a specific diagnostic trap: fatigue and muscle weakness are hallmark symptoms of both iron deficiency anemia, the condition Injectafer treats, and hypophosphatemia, the condition it can cause. A patient who still feels exhausted after an infusion may reasonably assume the anemia has not resolved rather than suspect a new problem. The FDA’s updated labeling also flags bone and joint pain, confusion, tremors, seizures and cardiac arrhythmias as signs that warrant urgent evaluation, and notes that chronic, severe cases can progress to osteomalacia, a softening of the bones, and fractures requiring clinical intervention.
What Changes at the Infusion Chair
Part of what has made Injectafer popular in busy infusion settings is speed: for adults weighing 50 kilograms or more, the label allows a full 1,500-milligram course delivered in just two visits at least seven days apart, or, in adults, a single-dose option of up to 1,000 milligrams given as one push over roughly 15 minutes. That convenience means each infusion delivers a comparatively large dose of iron at once, and the label’s own history ties post-marketing hypophosphatemia cases mostly to repeated exposure over multiple courses in patients with no prior history of kidney problems, though the agency notes some cases followed only a single dose. Prior courses within the past three months are exactly the scenario the new monitoring language targets.
Under the revised label, clinicians are expected to correct pre-existing low phosphate before starting treatment, monitor patients at ongoing risk of chronic low phosphate, and check serum phosphate before any repeat course given within three months of the last one. Severe or persistent hypophosphatemia should prompt permanent discontinuation. Generic versions of ferric carboxymaltose are expected to carry matching label updates. The FDA has said the reaction is largely preventable through appropriate monitoring and early intervention, but the agency has not set a target testing rate or a timeline for reassessing whether monitoring improves, leaving the pace of change largely in the hands of the clinics and infusion centers that administer the drug every day. Full details of the action are in the FDA’s drug safety communication, and the phosphate-monitoring language the warning elevates already appears in Injectafer’s prescribing information on file with the FDA.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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