What is the maximum recommended infusion rate for phosphate to avoid complications such as thrombophlebitis and metastatic calcium-phosphate deposition?

• A. 7 mmol/hour
• B. 5 mmol/hour
• C. 10 mmol/hour
• D. 12 mmol/hour

Answer: (A)

Infusing phosphate too rapidly increases the risk that calcium phosphate will precipitate both in the vein and in tissues, leading to vein irritation (thrombophlebitis) and metastatic calcium-phosphate deposition. Limiting the rate to seven millimoles per hour provides a safer balance between correcting phosphate needs and minimizing precipitation and local or systemic complications. If larger replacements are needed, they should be divided into slower infusions or adjusted with careful monitoring of serum phosphate and calcium.