Treatment of Hypophosphatemia
Intravenous phosphate is not completely benign. It is potentially dangerous because it can precipitate with calcium and cause hypocalcemia (because the phosphate binds to calcium), renal failure (due to calcium phosphate precipitation in the kidneys), and possibly fatal arrhythmias.
Because of that, only use IV phosphate when the serum phosphate level is < 1 mg/dL and patient has symptoms of hypophosphatemia.
A serum phosphate level of less than 2.8 mg/dL defines hypophosphatemia. However, only treat when it’s actually less than 2.0 mg/dL.
It’s very rare to have symptoms of hypophosphatemia with a serum phosphate > 2 mg/dL. Symptoms occur when the serum phosphate concentration is less than 2 mg/dL (0.64 mmol/L). Because of that, most hypophosphatemic patients will not require phosphate replacement unless their Phosphate level is less than 2. Treatment aimed at the cause is recommended for all levels of hypophosphatemia. E.g replace vitamin D in patients with vitamin D deficiency.
Oral repletion is most often achieved with a combined preparation of sodium and potassium phosphate. Sodium phosphate is preferred for intravenous therapy.
| Check serum phosphate levels every 6hours when giving IV phosphate. If the level gets to 1.5 mg/dL, switch to oral treatment if possible.
Stop IV repletion when the serum phosphate level is > 1.5 mg/dL and when oral therapy is possible. Stop phosphate replacement (IV or PO) when the serum phosphate is > 2.0 mg/dL unless there is an indication for chronic treatment such as urinary phosphate wasting |
IV Phosphate Replacement
Sodium phosphate is preferred for intravenous therapy. Potassium phosphate may also be used if potassium is low.
The most reliable method of ordering IV phosphate is by millimoles, then specifying the potassium or sodium salt.
• Phosphate replacement must be ordered in mmol of phosphorus.
• Use SODIUM phosphate for patients with serum potassium > 4.5 mEq/L and serum sodium < 145mEq/L
Standard Preparations of IV phosphate:
- Potassium Phosphate: 15 mmol/250 mL and 21 mmol/250 mL
- Sodium Phosphate: 15 mmol/250 mL, 21 mmol/250 mL, and 30 mmol/250 mL
| Current Serum Phosphorus Level | Total Phosphorus Replacement | Monitoring |
| ≥ 1.25 mg/dL | Sodium phosphate 15 to 30 mmol IV over 4-6hrs. It’s diluted in 250 ml of Normal saline. ie. 0.08 to 0.24 mmol/kg over 6 hours (up to a maximum total dose of 30 mmol). |
Recheck serum phosphorus level 2 hours after infusion complete |
| < 1.25 mg/dL | Sodium phosphate 30 mmol IV over 4-6hrs. May increase to a max of 80 mmol over 8 to 12 hours based on weight. See below. It’s diluted in 250 ml of Normal saline. i.e. 0.25 to 0.50 mmol/kg over 8 to 12 hours (up to a maximum total dose of 80 mmol). |
Recheck serum phosphorus level 2 hours after infusion complete |
Potassium Phosphate 15 or 30 mmol IV over 4-6hrs can also be used to replace phosphorus IV if potassium is also low as well. It’s diluted in 250 ml of Normal saline.
Oral Phosphate Replacement
Oral repletion is most often achieved with a combined preparation of sodium and potassium phosphate.
E.g. Phos NaK 250-500 mg 1 tab four times a day with meals and at bedtime.
K-Phos 1-2 tabs PO QID.
1 tab of K-phos = 250 mg phosphorus, 8 mmol phosphate, 1.1 mEq potassium, 13 mEq sodium.
Brands of combined preparations of Sodium Phosphate and Potassium Phosphate used for oral phosphate replacement.
K-Phos Neutral: Monobasic potassium phosphate 155 mg, dibasic sodium phosphate 852 mg, and monobasic sodium phosphate 130 mg [equivalent to elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)]
Phos-NaK: Dibasic potassium phosphate, monobasic potassium phosphate, dibasic sodium phosphate, and monobasic sodium phosphate per packet (100s) [sugar free; equivalent to elemental phosphorus 250 mg (8 mmol), sodium 160 mg (6.9 mEq), and potassium 280 mg (7.1 mEq) per packet; fruit flavor]
| Current Serum Phosphorus Level | Total Phosphorus Replacement | Monitoring |
| ≥ 1.5 mg/dL | 1 mmol/kg of elemental phosphorus (minimum of 40 mmol and a maximum of 80 mmol) can be given in 3 to 4 divided doses over a 24-hour period. | Recheck next AM |
| < 1.5 mg/dL | 1.3 to 1.4 mmol/kg of elemental phosphorus (up to a maximum of 100 mmol) can be given in three to four divided doses over a 24-hour period. | Recheck next AM |
If both potassium and phosphorus replacement required, subtract the mEq of potassium given as potassium phosphate from the total amount of potassium required. (Conversion: 3 mmols KPO4 = 4.4 mEq K+)
Call pharmacy for assistance if needed.
References
From: http://www.surgicalcriticalcare.net/Guidelines/electrolyte_replacement.pdf
The Washington Manual of Medical Therapeutics