Potassium Phosphate

All calculations should be independently verified prior to clinical use. These calculators are intended to supplement, not replace, clinical judgment.

Convert between phosphate (mmol), potassium (mEq), and volume (mL) for potassium phosphate injection. Enter a value in any row and click Calculate to populate the other two.

Medication error risk. Potassium phosphate contains unequal concentrations of potassium (4.4 mEq/mL) and phosphate (3 mmol/mL). Orders written in one unit are frequently misread as the other, which can result in significant under- or overdosing of either electrolyte. Always specify both the mmol of phosphate and the mEq of potassium when ordering, and verify with pharmacy.

Component	Amount		Unit
Phosphate (PO₄)			mmol
Potassium (K⁺)			mEq
Volume			mL

Potassium phosphate injection (Hospira) is a concentrated solution containing a mixture of potassium phosphate monobasic (KH₂PO₄) and potassium phosphate dibasic (K₂HPO₄). Each millilitre provides:

Component	Per mL	Per mmol PO₄	Per mEq K⁺
Phosphate (PO₄)	3 mmol	1 mmol	0.682 mmol
Potassium (K⁺)	4.4 mEq	1.467 mEq	1 mEq
Volume	1 mL	0.333 mL	0.227 mL

The conversion constant 0.6818 is the ratio of mmol PO₄ to mEq K⁺ (3 ÷ 4.4 = 0.6818). This asymmetry — 3 mmol PO₄ but 4.4 mEq K⁺ per mL — is the root cause of medication errors: an order for "3 mmol" and "3 mEq" differ by a factor of 4.4/3 = 1.47.

Typical dosing: Phosphate repletion in ICU patients is commonly 0.08–0.32 mmol/kg IV over 4–6 hours, depending on serum phosphate. Do not confuse with sodium phosphate or organic phosphate preparations, which have different concentrations.

References

Potassium Phosphates Injection [package insert]. Lake Forest, IL: Hospira Inc; 2004.
Kraft MD, Btaiche IF, Sacks GS, Kudsk KA. Treatment of electrolyte disorders in adult patients in the intensive care unit. Am J Health Syst Pharm. 2005;62(16):1663–1682.
ISMP (Institute for Safe Medication Practices). Phosphate confusion continues to cause serious medication errors. ISMP Medication Safety Alert. 2004;9(6).