Indications for hypophosphatemia correction

Based on the review, it is suggested to correct hypophosphatemia when it is acute and severe or symptomatic^7-12.

It is considered severe when levels are below 2 mg/dL¹².

In cases of moderate hypophosphatemia, oral supplementation may be considered.

Phosphate replacement can be administered enterally, by enema, or intravenously.

Oral phosphate supplementation

The formulation we suggest for oral administration is used in our setting for patients with renal failure who require external phosphate supplementation. It is known as Jolie's solution, a compounded preparation made upon request¹³.

This solution contains, per ml: 1 mmol of phosphate and 1 mEq of sodium¹³.

Its composition is as follows:

Adverse effects of oral phosphate administration include diarrhea, nausea, vomiting, and abdominal pain¹³. In case of overdose, it may cause hyperphosphatemia, hypocalcemia, hypokalemia, hypernatremia, and acute kidney injury¹³.

The suggested oral supplementation is 2-3 times the normal dietary intake, depending on tolerance, divided into 2 to 3 doses. A table is attached showing the recommended dietary intake by age, according to the World Health Organization (WHO), and it varies depending on the age of the child.

According to other authors, 2-3 mmol/kg/day may also be considered.

Table 4 shows the recommended dietary phosphorus intake by age, expressed in mg and mmol per day.

Table 4 Recommended dietary phosphorus intake according to the World Health Organization 

It should be noted that active vitamin D is required for intestinal phosphate absorption¹⁴.

Commercial phosphate formulations are available for use as oral laxatives or enemas. Some studies have shown a safe increase in phosphate levels in the ICU setting¹⁶.

In our sphere, this oral solution contains disodium phosphate 900 mg/5 mL (180 mg/mL) and monosodium phosphate 2.4 g/5 mL (0.48 mg/mL). Since it acts as a laxative, it can cause the previously mentioned gastrointestinal complications; therefore, we recommended not administering more than 5 mL of the solution for the correction of hypophosphatemia and monitoring for the appearance of adverse symptoms.

Intravenous phosphate supplementation

Vials for intravenous use are available for cases that are severe and/or symptomatic, or in specific situations where there is poor tolerance to oral or enteral phosphate.

The vial contains 20 ml of sodium glycerophosphate (Glycophos); each ml provides 1 mmol of phosphate and 2 mmol of sodium¹. Glycerophosphate requires hepatic hydrolysis and normal alkaline phosphatase levels¹⁷.

Compatible solvents include normal saline and 5% dextrose. The solution should be diluted to reach the maximum suggested concentration, which varies according to the available venous access. The maximum concentration is 0.12 mmol/ml for central lines and 0.05 mmol/ml for peripheral lines^12-18. It is recommended to administer it over 6 hours, not exceeding an infusion rate of 0.6 mmol/kg/hour.

Table 5 shows the suggested phosphate doses (in mmol) according to the degree of plasma phosphate depletion in children^12-19.

Table 5 Severity levels of hypophosphatemia and suggested doses (mmol) for intravenous correction 

In adults, the approximate correction is 10 to 20 mmol/dose (half a vial or one vial), which is the maximum dose, regardless of weight.

Some authors suggest subsequent intravenous maintenance when hypophosphatemia is severe. The suggested maintenance doses are as follows¹²:

Keep in mind that hypophosphatemia may occur with low, moderate, or even high phosphate stores, since the decrease in plasma phosphate levels can result from a transmembrane shift of phosphate. For this reason, phosphate maintenance should be individualized. For instance, in a severely malnourished patient with refeeding syndrome, where phosphate stores are presumed to be depleted, supplementation may be incorporated into the patient’s parenteral nutrition if applicable.

As a practical example, consider a 1-year-old child weighing 10 kg who presents with severe symptomatic hypophosphatemia and a plasma phosphate level of 1 mg/dl. As mentioned earlier, the recommended correction is 0.16 mmol/kg, which, when multiplied by the child’s weight, results in a total dose of 1.6 mmol to be administered.

As previously mentioned, 1 ml of sodium glycerophosphate (Glycophos) contains 1 mmol of phosphate and 2 mmol of sodium. Therefore, to correct 1.6 mmol, we would draw 1.6 mL from the vial and dilute it according to the available venous access.

If a central venous line is available (maximum concentration 0.12 mmol/mL), the dilution would be as follows: 1.6 mL of sodium glycerophosphate should brought up to 15 mL with normal saline and administered over 6 hours at a 2.5 mL/hour rate.

The dilution mentioned above represents the maximum concentration allowed based on osmolarity. If deemed appropriate, it may be further diluted in a larger volume of saline.

If peripheral venous line is available (maximum concentration 0.05 mmol/ml), the dilution would be as follows: 1.6 mL of sodium glycerophosphate should brought up to 35 mL with normal saline and administered over 6 hours at a 5.8 mL/hour rate.

The same considerations regarding dilution as in the previous case apply.