What are the side effects of ferric carboxymaltose (FCM)?

Side Effects of Ferric Carboxymaltose (FCM)

Hypophosphatemia is the most clinically significant adverse effect of ferric carboxymaltose, occurring in 47-75% of treated patients, with severe and prolonged cases potentially leading to osteomalacia and fractures—making FCM dangerous for patients requiring repeat infusions. 1

Common Adverse Effects

Hypophosphatemia (Most Important)

• Incidence ranges from 47-75% with FCM compared to <10% with other IV iron formulations (low molecular weight iron dextran, ferumoxytol, ferric derisomaltose). 1
• In clinical trials, 51% of FCM-treated patients developed hypophosphatemia (<2 mg/dL) at any time from baseline to Day 35. 1
• Severe hypophosphatemia can persist up to 6 months after FCM administration, though the true duration remains unknown. 1
• The mechanism involves FCM triggering a sharp increase in intact fibroblast growth factor-23 (iFGF23), leading to hyperphosphaturic hypophosphatemia. 1

Clinical Manifestations of Hypophosphatemia

• Symptoms include fatigue, proximal muscle weakness, bone pain, arthralgia, asthenia, myopathy, and respiratory failure—symptoms that can mimic iron deficiency anemia itself. 1, 2
• Severe cases can progress to osteomalacia, Looser zones (pseudofractures), and low-trauma fractures with repeated FCM dosing. 1, 3
• The "6H syndrome" describes the full constellation: hypophosphatemia, hyperphosphaturia, hypovitaminosis D, hypocalcemia, secondary hyperparathyroidism, and high FGF23. 4

Other Common Adverse Effects (FDA Label Data)

• Hypophosphatemia (2.1%), dysgeusia (1.2%), nausea (7.2%), hypertension (4%), erythema (3%), flushing (4%), vomiting (2%), injection site discoloration (1.4%), and hypotension (1%). 5
• In pediatric patients: hypophosphatemia (13%), injection site reactions (8%), rash (8%), headache (5%), vomiting (5%). 5

Infusion-Related Reactions

• Minor infusion reactions occur in 1-3% of patients, with serious adverse events being rare. 6
• Most reactions are complement activation-related pseudo-allergies (CARPA) rather than true IgE-mediated allergic reactions. 6
• Severe life-threatening anaphylaxis is extremely rare but constitutes a medical emergency when it occurs. 1

High-Risk Populations for Hypophosphatemia

FCM should be avoided in patients requiring repeat infusions, as cumulative dosing increases the risk of osteomalacia and fractures. 1

Specific High-Risk Groups:

• Recurrent or ongoing blood loss: abnormal uterine bleeding, hereditary hemorrhagic telangiectasia, gastrointestinal bleeding. 1
• Malabsorptive disorders: bariatric surgery, inflammatory bowel disease, celiac disease. 1, 4
• Normal renal function (higher glomerular filtration rate allows greater phosphate excretion). 1
• Severe iron deficiency, lower body weight, low baseline serum phosphate, higher serum parathyroid hormone. 1

Importantly, patients with impaired kidney function have a lower risk of developing hypophosphatemia due to reduced GFR limiting filtered phosphate. 1 In heart failure populations, the incidence of moderate or severe hypophosphatemia was only 8.1%, compared to 30-56% in other therapeutic areas. 7

Pregnancy-Specific Considerations

• Severe hypersensitivity reactions can cause fetal bradycardia, especially during the second and third trimester. 5
• Published data have not established an association between FCM and major birth defects or miscarriage, though studies cannot exclude all drug-related risks. 5
• Animal studies showed fetal malformations and spontaneous abortions at maternally toxic doses. 5

Post-Marketing Adverse Events

The following have been reported in post-marketing surveillance: 5

• Cardiovascular: tachycardia, chest discomfort
• Musculoskeletal: arthralgia, back pain, hypophosphatemic osteomalacia
• Neurologic: syncope
• Respiratory: dyspnea
• Dermatologic: angioedema, erythema, pruritus, urticaria
• Metabolic: hypophosphatemia
• General: chills, pyrexia
• Pregnancy: fetal bradycardia

Management Recommendations

Monitoring Strategy

• Routine phosphate monitoring is NOT recommended for low-risk patients receiving a single FCM infusion, as most hypophosphatemia is asymptomatic and transient. 8
• Phosphate monitoring IS recommended for patients at increased risk: those receiving multiple infusions, higher cumulative doses, long-term treatment, or with underlying clinical risk factors. 1, 8
• The UK Medicines and Healthcare products Regulatory Agency advises monitoring serum phosphate in high-risk patients. 6

Treatment of Hypophosphatemia

• Prophylactic oral phosphorus is unlikely to be effective and is not recommended for routine practice. 8
• Severe cases may require continuous intravenous phosphate infusions for weeks, along with activated vitamin D (calcitriol) and dietary optimization. 4
• Symptoms lasting more than a few days should be evaluated by a provider and may require premedication or an alternative IV iron formulation for subsequent therapy. 1

Alternative Formulations

For patients requiring repeat infusions, iron sucrose or ferric derisomaltose should be chosen instead of FCM due to their significantly lower hypophosphatemia rates (1-4% vs 47-75%). 6, 3 Iron sucrose carries only a 1% hypophosphatemia risk, making it suitable for repeated dosing. 6