Potassium Phosphate Ampule Content
A standard ampule of potassium phosphate injection contains 3 mmol (millimoles) of phosphorus per milliliter and 4.4 mEq of potassium per milliliter. 1
Standard Formulation Details
The FDA-approved potassium phosphate injection (Potassium Phosphates Injection, USP 3 mM P/mL) contains the following per milliliter: 1
- Phosphorus content: 3 mmol/mL (93 mg/mL)
- Potassium content: 4.4 mEq/mL (170.3 mg/mL)
- Composition: 224 mg monobasic potassium phosphate (anhydrous) and 236 mg dibasic potassium phosphate (anhydrous) per mL
- Osmolar concentration: 7.4 mOsmol/mL 1
Clinical Dosing Context
Important note: This product must not be administered undiluted and requires dilution in large volume infusion fluids for intravenous use. 1
Phosphate Replacement Dosing
When treating hypophosphatemia in critically ill patients: 2
- Mild-to-moderate hypophosphatemia (serum phosphate 1.27-2.48 mg/dL): 15 mmol total dose administered over 3 hours achieves normalization in approximately 81% of cases
- Severe hypophosphatemia (serum phosphate ≤1.24 mg/dL): 30 mmol total dose administered over 3 hours achieves normalization in approximately 30% of cases, with many patients requiring additional supplementation 2
An individualized approach using the formula: Phosphate dose (mmol) = 0.5 × Body Weight (kg) × (1.25 - [serum Phosphate in mmol/L]) administered at 10 mmol/hour has demonstrated 98% efficacy in achieving post-infusion phosphate levels >0.6 mmol/L without causing hyperphosphatemia or hyperkalemia. 3
Pediatric Parenteral Nutrition Context
In parenteral nutrition formulations, phosphorus can be provided as inorganic salts including sodium and potassium phosphate, with dosing requirements varying by age: 4
- Preterm infants (first days): 1.0-2.0 mmol/kg/day
- Growing premature infants: 1.6-3.5 mmol/kg/day
- Term infants 0-6 months: 0.7-1.3 mmol/kg/day
- Infants 7-12 months: 0.5 mmol/kg/day
- Children 1-18 years: 0.2-0.7 mmol/kg/day
Critical Safety Considerations
Potassium load: Each milliliter delivers 4.4 mEq of potassium, requiring careful monitoring to avoid hyperkalemia, particularly in patients with renal impairment or those receiving other potassium-containing medications. 1
Precipitation risk: Neutral potassium phosphate (K₂HPO₄) carries a risk of precipitation with calcium salts, which limits its use in parenteral nutrition solutions. 4 Phosphate should be added at the end of the compounding process after calcium has been mixed with amino acids and glucose. 4
Monitoring requirements: Approximately 45-60% of patients develop recurrent hypophosphatemia within 24-48 hours after initial correction, necessitating continued supplementation and monitoring. 2