Phosphate

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    Introduction

    • Normal Phosphate 0.8 - 1.6 mmol/L (SI)
      • 2.5 - 5 mg/dL

    Hypophosphatemia

    • Serum PO4 < 0.81 mmol/L
    • Causes:
      • Alcoholism, Critical Illness, malnutrition
      • Other:
        • Kidney Phosphate Wasting (Acetaminophen, Vitamin D deficiency/resistance, hyperparathyroidism, osmotic diuresis, oncogenic osteomalacia, renal transplant, fanconi syndrome (pRCA Type II), tenofovir, ifosfamide (prox RTA), hypophosphatemic ricketts
        • Chronic diarrhea, decreased absorption
        • Refeeding Syndrome Post-starvation (intracellular PO4 intake)
        • Treatment of DKA
        • Parathyroidectomy ("Hungry Bone Syndrome")
        • Respiratory Alkalosis
    • Symptoms:
      • Many patients are asymptomatic (even at very low phosphate levels < 0.32)
      • PO4 < 0.65 mmol/L (< 2mg/dL)
        • Weakness
      • PO4 < 0.32 mmol/L (< 1mg/dL)
        • Respiratory muscle weakness, rhabdomyelysis, hemolysis
        • Hemolysis
        • Decrease in cardiac output (weaker myocardial contractility)
        • Shift of Oxyhemoglobin Sat curve (less tissue oxygen extraction)
    • Assessment:
      • Urine Wasting?
        • 24hr urine phosphate (> 32.3 mmol/L if renal losses)
        • Fractional Excretion of Phosphate (FePO)
    • Treatment:
      • Supplement Phosphate
      • Use PO 
      • Only give IV if PO4 < 0.32 mmol/L (<1 mg/dL) and symptomatic
        • IV phosphate causes risk of hypocalemia and acute kidney injury.
        • Monitor PO4 q6h, limit intake to 80 mmol in 24hrs.
      • Serum Phosphate:

        • > 0.6 mmol/L: 0.08 to 0.16 mmol/kg phosphate IV once

     

    • 0.4 - 0.6 mmol/L: 0.16 to 0.32 mmol/kg phosphate IV once
    • < 0.4 mmol/L: 0.32 to 0.64 mmol/kg phosphate IV once
    • Max 24hr dose = 80 mmol
    • Renally Adjust:

      • CrCL < 0.8 mL/s, reduce dose by 25 to 50%

      •  

        CrCl < 0.4 mL/s, reduce dose by 50 to 75%

         

    • Solution   PO4- Potassium Sodium
      Sodium Phosphate IV IV 3 mmol/mL   4.0 mEq/L
      Potassium Phosphate IV IV 3 mmol/mL 4.4 mmol/mL  

      Sodium Phosphate (Phoslax)

       

      PO 4mL

      514.6mg

      (16.6 mmol)

       

      443.24mg

      (19.28 mmol)

      Sodium Phosphate 500mg tab

        (Phosphate Novartis)

      PO 1 tab

      500 mg

      (16.1 mmol)

      123 mg

      (3.1 mmol)

      469 mg

      (20.4 mmol)


       
    • NOTE: Correct way to order is i.e. "phosphate 10mmol (as sodium phosphate) IV over 3 hours"
      • (must specify which component and which salt, and how much)
    •    
      Severe PO4 + Adverse Effects IV 0.9 mg/kg/hr (monitor PO4 q6h) [1 mmol = 31mg]
      Severe PO4 IV 0.6 mg/kg/hr (monitor PO4 q6h)
      PO4 > 0.65 mmol/L

      PO 1200-1500 mg phosphorus daily

      (Neutra-Phos or K-Phos)

      Maintenance

      1200mg PO daily OR (70% bioavailability)

      800 mg IV daily 

    Hyperphosphatemia

    • Most common causes:
      • CKD
      • Acute phosphate nephropathy
      • Large phosphate intake (such as bowel prep)
      • Tumor Lysis Syndrome
      • Rhabdomyolysis
    • Treatment:
      • Can use aluminum-containing antacids (or sucralfate) - binds PO4 in GI.
      • If phosphate elevated, and patient is oliguric, then dialysis may be indicated
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