How many milliequivalents (mEq) of potassium are in 1 ampule of potassium phosphate?

Potassium Content in 1 Ampule of Potassium Phosphate

One ampule of potassium phosphate contains 22 mEq of potassium in a 5 mL vial (4.4 mEq/mL) as indicated by the FDA drug label. 1

Potassium Phosphate Composition

Potassium phosphate injection is a concentrated solution containing a mixture of monobasic potassium phosphate and dibasic potassium phosphate in water for injection. The specific composition per the FDA label is:

• Each 5 mL ampule (single-dose vial) contains:

  • Phosphorus: 15 mmol (3 mmol/mL)
  • Potassium: 22 mEq (4.4 mEq/mL) 1

• Each 15 mL vial contains:

  • Phosphorus: 45 mmol (3 mmol/mL)
  • Potassium: 66 mEq (4.4 mEq/mL) 1

Clinical Considerations for Administration

Important Warnings

• Potassium phosphate MUST BE DILUTED before administration
• Never administer as an undiluted bolus or rapid IV push due to risk of serious cardiac adverse reactions 1
• Monitor for hyperkalemia, especially in patients with renal impairment
• Monitor for hyperphosphatemia and resulting hypocalcemia

Dosing Considerations

• When needed for phosphate replacement in DKA, 20–30 mEq/L potassium phosphate can be added to replacement fluids 2
• For hypophosphatemia treatment in critically ill patients:
  • Mild-moderate hypophosphatemia: 15 mmol phosphate (22 mEq potassium) has been shown to be effective and safe 3
  • Severe hypophosphatemia: 30 mmol phosphate (44 mEq potassium) may be required 3

Contraindications

• Severe renal impairment (eGFR less than 30 mL/min/1.73 m²) or end-stage renal disease 1
• Hyperkalemia
• Severe hyperphosphatemia

Monitoring Parameters

• Serum potassium, phosphorus, calcium, and magnesium concentrations should be monitored during therapy
• ECG monitoring is recommended during administration of high doses or in patients with cardiac conditions
• More frequent monitoring is required for patients with:
  • Moderate renal impairment
  • Cardiac comorbidities
  • Concomitant medications affecting potassium levels 4

Potential Adverse Effects

• Hyperkalemia: cardiac conduction disturbances, arrhythmias, hypotension
• Hyperphosphatemia: hypocalcemia, tissue calcification
• Vein damage and thrombosis with peripheral administration
• Aluminum toxicity with prolonged use, especially in patients with renal impairment 1

Clinical Pearls

• Potassium phosphate is often used when both potassium and phosphate replacement are needed
• For patients requiring phosphate without additional potassium, sodium phosphate formulations may be preferred
• Redevelopment of hypophosphatemia is common (45-60% of cases) within 2 days of initial correction, requiring ongoing monitoring and potential additional supplementation 3
• Phosphate replacement may sometimes be indicated in patients with cardiac dysfunction, anemia, or respiratory depression and in those with serum phosphate concentration <1.0 mg/dl 2

Remember that potassium phosphate is a concentrated electrolyte solution that requires careful administration, appropriate dilution, and monitoring to prevent potentially serious adverse effects.