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Iron infusions are an essential treatment for iron deficiency anemia, particularly when oral iron supplements are ineffective or poorly tolerated. However, some patients experience flu-like symptoms after an iron infusion or develop hypophosphatemia (low phosphate levels). Understanding these side effects can help patients and healthcare providers make informed decisions about treatment options.

Flu-Like Symptoms After Iron Infusion

Some people report feeling unwell after an iron infusion, experiencing:

• Fever or chills
• Muscle aches (myalgia)
• Joint pain (arthralgia)
• Fatigue
• Headache

These symptoms usually resolve within 24–72 hours and are linked to a temporary rise in inflammatory markers such as interleukin-6 (IL-6) (Auerbach et al., 2020). Research suggests ferric carboxymaltose (FCM) may have a higher likelihood of causing temporary flu-like symptoms than other IV iron formulations (Schaefer et al., 2022).

Hypophosphatemia and Iron Infusion: What You Should Know

Hypophosphatemia, or low phosphate levels in the blood, is an increasingly recognized complication of IV iron therapy, particularly with ferric carboxymaltose (FCM).

Symptoms of Hypophosphatemia

• Fatigue
• Muscle weakness
• Bone pain
• Softening of bones (osteomalacia)
• Fractures

Who is at Higher Risk?

Certain factors increase the likelihood of developing iron infusion-induced hypophosphatemia:

• Low pre-infusion phosphate levels (<1.0 mmol/L)
• Normal kidney function (FCM increases phosphate excretion)
• Severe iron deficiency anemia
• Vitamin D deficiency, affecting phosphate absorption
• Bariatric surgery, malabsorption disorders, hyperparathyroidism, older age, and low body weight (Fukumoto et al., 2023; Glaspy et al., 2021)

How to Prevent Hypophosphatemia After an Iron Infusion

To minimise risks, healthcare providers should:

• Assess medical history – Ask about past iron infusion reactions, kidney health, and endocrine disorders.
• Perform blood tests before infusion – Check serum phosphate, vitamin D, calcium, and parathyroid hormone (PTH) levels.
• Monitor phosphate levels after infusion – High-risk patients should have phosphate levels checked 1–2 weeks post-infusion (Strubbe et al., 2024).
• Consider alternative IV iron options – Ferric derisomaltose (FDI), iron sucrose, or ferumoxytol may reduce hypophosphatemia risk.

Managing Flu-Like Symptoms and Side Effects

If you experience flu-like symptoms after an iron infusion, try the following:

• Hydrate well before and after treatment
• Take over-the-counter pain relief like paracetamol or ibuprofen
• Rest for 24–48 hours after infusion

Seek medical attention if you experience:

• Severe fatigue, muscle weakness, or persistent bone pain
• Difficulty breathing or chest pain

Why Choose the Right IV Iron Therapy?

Choosing the best iron infusion clinic and IV iron formulation can reduce side effects and improve patient experience. If you’re considering an iron infusion for anemia, consult a healthcare provider to discuss risk factors and the best options available.

References

• Auerbach M, Macdougall IC. (2020). Safety of intravenous iron formulations: A comparative review. CMAJ, 192(43), E1288–E1294.
• Schaefer B, Tobiasch M, Wagner S, et al. (2022). Hypophosphatemia after intravenous iron therapy: Comprehensive review. Bone, 154, 116202.
• Fukumoto S, Murata T, Osuga Y, Pollock RF. (2023). Incidence of Hypophosphatemia After Intravenous Iron. Advances in Therapy, 40(10), 4877–4888.
• Glaspy JA, Wolf M, Strauss WE. (2021). Intravenous Iron-Induced Hypophosphatemia. Advances in Therapy, 38(7), 3531–3549.
• Strubbe M, David K, Peene B, et al. (2024). Hypophosphatemia following intravenous iron administration. Reviews in Endocrine and Metabolic Disorders.