RFT – Phosphate

HYPOPHOSPHOTEMIA

ABCs

  • Check vitals
  • Confirm < 0.81 mmol/L
  • Always investigate and treat the underlying cause, e.g., refeeding, alcohol use, sepsis, DKA
  • Assess for symptoms
    • Muscle pain or weakness
    • Respiratory failure
    • Heart failure
    • Neurologic signs (confusion, seizures, irritability, coma)

Major Causes of Hypophosphatemia

Internal Redistribution
  • Increased insulin secretion (e.g., refeeding)
  • Acute respiratory alkalosis
  • Hungry bone syndrome
Decreased Intestinal Absorption
  • Inadequate dietary intake
  • Inhibition of phosphate absorption (e.g., antacids, phosphate binders, niacin)
  • Steatorrhea and chronic diarrhea
  • Vitamin D deficiency or resistance
Increased Urinary Excretion
  • Primary or secondary hyperparathyroidism
  • Vitamin D deficiency or resistance
  • Hereditary hypophosphatemic rickets
  • Oncogenic osteomalacia
  • Fanconi syndrome
Drug- and Toxin-Induced Loss
  • Acetazolamide
  • Antacids (aluminum- or magnesium-based)
  • Bisphosphonates
  • Niacin
  • Phosphate binders
  • Valproate
  • Insulin
  • Antiretrovirals:
    • Tenofovir
    • Adefovir
    • Cidofovir
  • Chemotherapy:
    • CAR-T cell therapy (e.g., tisagenlecleucel, axicabtagene)
    • Cisplatin
    • Ifosfamide
    • Tyrosine kinase inhibitors (e.g., imatinib)
    • VEGF inhibitors (e.g., sorafenib)
  • Denosumab
  • Heavy metals (cadmium, lead, arsenic)
  • IV iron (esp. ferric carboxymaltose)
  • mTOR inhibitors (e.g., temsirolimus)
Loss via Kidney Replacement Therapy
  • Phosphate loss during dialysis or other renal replacement therapies

MANAGEMENT

  • If > 0.64 mmol/L -> observe
  • If < 0.32 mmol/L -> IV phosphate
  • If phosphate is 0.32 to 0.64 mmol/L
    • Symptomatic: Treat based on exact level (IV vs oral)
    • Asymptomatic: Treat with oral phosphate
  • Potassium check
    • K < 4.0 mmol/L → Potassium Phosphate
    • K ≥ 4.0 mmol/L → Sodium Phosphate

IV Phosphate Dosing

  • 0.36–0.45 mmol/L
    • 0.2 mmol/kg IV over 4 hrs
  • 0.32–0.36 mmol/L
    • 0.3 mmol/kg IV over 4 hrs
  • < 0.32 mmol/L
    • Up to 30 mmol IV over 6 hrs
  • Monitor phosphate 6 hours after
  • IV Infusion Preparation Options
    • Potassium Phosphate 10 mL in 150–250 mL NS over 6 hours
    • Sodium Phosphate 10 mL in 150–250 mL NS over 6 hours

Dosing may vary; consult the pharmacy for availability and compatibility

Available IV Phosphate Formulations (MOH)

  • Potassium Phosphate 1 vial = 15 mL = 66 mEq K⁺ = 45 mmol phosphate
  • Sodium Glycerophosphate (Glycophos®) 1 ampule = 20 mL = 40 mmol Na⁺ = 20 mmol phosphate
  • Disodium Glucose-1-Phosphate Tetrahydrate (Phocytan®) 1 ampule = 10 mL = 13.3 mmol Na⁺ = 6.6 mmol phosphate

Oral Phosphate Repletion

  • 0.48–0.64 mmol/L
    • 1 mmol/kg/day in 3–4 divided doses (max ~80 mmol/day)
  • 0.32–0.48 mmol/L
    • 1.3–1.4 mmol/kg/day in 3–4 doses (max ~100 mmol/day)
  • Monitor after 12–24 hrs and adjust

Available Oral Phosphate Formulations (MOH)

  • Sodium Acid Phosphate (Phosphate Sandoz®) Effervescent 1 tab = 3.1 mmol K⁺ + 20.4 mmol Na⁺ + 16.1 mmol phosphate

ESCALATION

  • Recheck phosphate after correction
  • Reassess the need for ongoing repletion
  • Call for help if
    • Patient unstable
    • Phosphate remains low despite adequate treatment

🔗 Related External Links

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