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Phosphate Dosing

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Current phosphate level
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Phosphate supplementation

Summary Phosphorus Content
K-Phos ® Neutral Tablets K-PHOS® ORIGINAL
Neutra-Phos ® Hypophosphatemia

Summary top of page

Phosphate Summary:
Phosphorus: (hypophosphatemia)
-Oral: ~2 packets (16 mmol) Neutra-Phos qid (with meals and at bedtime).
RDA: (1 packet qid = 1 gram phosphorus = 32 mmol)

Phosphates   
Phosphate supplement: Oral: Elemental phosphorus 250 to 500 mg 4 times/day after meals and at bedtime.  
P (MW=31).  250mg = 8.06 mmol.   RDA (adults): 800-1200mg phosphorus/day =  ~26 - 38 mmol/day.  (pregnant/lactating women: 1200mg/day).

Phosphorus Content top of page

Product P (mmol) Na+ meq K+ meq
Oral
Neutra-Phos®  (capsule /pkt) 8 7.1 7.1
Neutra-Phos K® (capsule /pkt) 8 0 14.25
Skim milk per 8 oz (1 cup) 8 3 5
K-Phos ® Neutral  (tablet) 8 13 1.1
Fleet® Phospho Soda (soln) /ml 4.15 4.82 0
IV
Potassium Phosphate (ml) 3 0 4.4
Sodium Phosphate (ml) 3 4.0 0
3 mmol = 93 mg phosphorus (MW = 31)

K-Phos ® Neutral Tablets top of page

K-hos ® Neutral Tablets: [ Each tablet contains approximately 250 mg of phosphorus, 298 mg of sodium (13.0 mEq) and 45 mg of potassium (1.1 mEq).]

 Dosage and administration:
Tablets should be taken with a full glass of water, with meals and at bedtime. Adults: One or two tablets four times daily. Pediatric Patients over 4 years of age: One tablet four times daily.

K-PHOS® ORIGINAL top of page

K-PHOS® ORIGINAL (Sodium Free): Each tablet contains potassium acid phosphate 500 mg [~ 114 mg (3.68 mmol) of phosphorus and 144 mg of K+ ( 3.7 mEq)]. ACTIONS: highly effective urinary acidifier.
INDICATIONS
: For use in patients with elevated urinary pH. Helps keep calcium soluble and reduces odor and rash caused by ammoniacal urine. Also, by acidifying the urine, it increases the antibacterial activity of methenamine mandelate / hippurate. DOSAGE:: Two tabs ( dissolved in 6-8 oz. of water) 4 times daily with meals and at bedtime. 

Neutra-Phos ® top of page

Neutra-Phos ®: (mix with at least 2.5 ounces (75 ml) of water/juice).
Dosage: 1 pkt four times daily with meals and at bedtime. Mild laxative effect possible.
[1 packet equivalent to elemental phosphorus 250 mg (~8 mmol), sodium 164 mg (7.1 mEq), and potassium 278 mg (7.1 mEq) per packet].

Dave's Tip: Remember that 1 pkt qid = RDA (1000 mg Phosphorus).
Table below (oral therapy for hypophosphatemia) shows that ~2 pkt's qid for treatment and 1 pkt for supplementation. [0.2 mmol x 70kg x 4 (e.g q6h) = 56 mmol = ~14 mmol (2 pkts) qid]

Hypophosphatemia  top of page

NORMAL LEVELS: 2.4 - 4.5 mg/dl (0.8 - 1.5 mmol/L)
Causes:   Decreased intake: malnutrition, malabsorption, vitamin D deficiency, phosphate binders, alcoholism.   Shifts from serum into cells: respiratory alkalosis, refeeding, hyperalimentation, effects of insulin/glucagon/androgens.  Increased urinary secretion: renal tubular defect, DKA.

Signs (generally seen only with total body depletion and serum PO4 < 1 mg/dL): weakness, rhabdomyolysis, respiratory compromise/failure, CHF, paresthesias, confusion, stupor, seizures, coma, hemolysis, platelet dysfunction, metabolic acidosis.

Therapy: Determine Ca x PO4 product before administering phosphorus:  If the product is greater than 60 mg/dl, there is a risk of calcium phosphate precipitation in the cornea, lung, kidney, cardiac conduction system, and blood vessels. 

Oral therapy:  For Phosphorus > 1 mg/dl (>0.3 mmol/L), oral therapy may be used.
1-2 tabs/pkts (8-16 mmol)  TID-QID.  
   [0.2 mmol x 70kg x 4 (e.g q6h) = 56 mmol = ~14 mmol (2 pkts) qid]

Estimated Phosphorus Requirements  top of page
(0.2-0.3 mmol/kg q6h = number of packets of Neutra-Phos®/24 hrs)
Patient weight  # pkts/24hr 0.2 -0.3 mmol/24hr 0.25 mmol/kg
60 kg 6 - 9   15
70 7 - 10.5 56-84 (14-21 mmol q6h) 17.5
80 8 - 12 64-96 (16-24 mmol q6h) 20
90 9 - 13.5 72-108 (18-27 mmol q6h) 22.5
100 10 - 15 80-120 (20-30 mmol q6h) 25
As a guideline, the phosphorus level will increase by an average of 1.2 mg/dl with a dose of 0.25mmol/kg.  Monitoring (IV): Phosphorus levels should be drawn at the end of the infusion and should always be drawn prior to any additional doses administered.     


IV REPLACEMENT:   
For Phosphorus < 1 mg/dl (< 0.3mmol/L).
Acute decreases in PO4: 0.25 mmol/kg IBW*  (infuse over 4-6 hours)
Chronic depletion of PO4: 0.5 mmol/kg IBW* (infuse over 6 hours)
Renal insufficiency (CrCL <20ml/min): reduce dose by 50%.

Preparation
Floors: KPhos or NaPhos 15 mmol/250 ml
ICU's:  KPhos or NaPhos 15 mmol/100ml NS/D5W over 2 hours centrally. (This method of administration is NOT recommended if: total calcium is < 7.5 mg/dL or > 11 mg/dL (corrected for albumin**) phosphorus is > 2 mg/dL OR significant renal dysfunction (Clcr < 10 ml/min).

Note: Phosphorus has historically been administered over 4 to 6 hours due to the potential risk associated with high doses and rapid administration (i.e., hypocalcemia, hypotension, metastatic calcification, renal failure). However, most of this data comes from cases of hypercalcemia treated with large doses of intravenous phosphates in which phosphorus levels were typically normal. More aggressive electrolyte replacement is not considered as risky.

References:

1 Bollaert PE, Levy B, Nace L, Laterre PF, Larcan A. Hemodynamic and metabolic effects of rapid correction of hypophosphatemia in patients with septic shock. Chest 1995 Jun;107(6):1698-701
2 Charron T, Bernard F, Skrobik Y, Simoneau N, Gagnon N, Leblanc M. Intravenous phosphate in the intensive care unit: More aggressive repletion regimens for moderate and severe hypophosphatemia. Intensive Care Med. 2003 Aug;29(8):1273-8. Epub 2003 Jul 05.   "In summary, ICU patients are prone to hypophosphatemia which can lead to several physiological alterations in cell function. These potential deleterious effects are reversed by phosphate supplementation. Rapid correction of phosphate deficit, as demonstrated here, appears safe. To prevent additional insult to tissues from phosphate deficit and because phosphate infusion is incompatible with many other medications we suggest infusing phosphate in the following manner: 30 mmol potassium phosphate over 2 h or 45 mmol over 3 h in patients with a baseline serum potassium below 4.0 mmol/l and creatinine below 200 µmol/l. Slower protocols (i.e., 30 mmol potassium phosphate over 4 h or 45 mmol over 6 h) or sodium phosphate (which is more expensive) are as efficacious and should be favored if kalemia is a concern."
3 Clark CL, Sacks GS, Dickerson RN, Kudsk KA, Brown RO. Treatment of hypophosphatemia in patients receiving specialized nutrition support using a graduated dosing scheme: results from a prospective clinical trial. Crit Care Med 1995 Sep;23(9):1504-11.
4 Kingston M, Al-Siba'i MB. Treatment of severe hypophosphatemia. Crit Care Med 1985 Jan;13(1):16-8.

"A 4-h infusion of 310 to 465 mg (10 to 15 mMol) phosphorus given to 28 of 31 consecutive seriously ill hypophosphatemic patients increased the serum phosphorus level above 1.2 mg/dl in all but one patient. There was no significant change in the mean serum calcium, potassium or blood pressure, no patient deteriorated, and six patients were stronger and more alert after the infusion. In seriously ill patients we recommend a 4-h infusion of 15 mg/kg (0.5 mMol/kg) phosphorus if the serum phosphorus is less than 0.5 mg/dl, or a 7.7-mg/kg (0.25 mMol/kg) infusion if the serum phosphorus is between 0.5 and 1.0 mg/dl."
5 Lentz, RD, Brown, DM, Kjellstrand, CM. Treatment of severe hypophosphatemia. Ann Intern Med 1978; 89:941. 
6 Miller DW, Slovis CM. Hypophosphatemia in the emergency department therapeutics. Am J Emerg Med 2000 Jul;18(4):457-61.
"Severe hypophosphatemia, as defined by a serum level below 1.0 mg/dL, may cause acute respiratory failure, myocardial depression, or seizures."
Summary: Administering K2PO4 at a rate of 1 mL (3 mMol) per hour is almost always a very safe and appropriate treatment for hypophosphatemia. 
7 Perreault MM, Ostrop NJ, Tierney MG.  Efficacy and safety of intravenous phosphate replacement in critically ill patients. Ann Pharmacother 1997 Jun;31(6):683-8.
" CONCLUSIONS: The administration of potassium phosphate 15 mmol to critically ill patients with mild-to-moderate hypophosphatemia over 3 hours is both effective and safe. The administration of potassium phosphate 30 mmol to severely hypophosphatemic patients was safe but achieved normalization of serum phosphate in a minority of patients. Either a higher dose or the subsequent administration of more potassium phosphate may be required to normalize serum phosphate concentrations. Once normalization has occurred, there is a high likelihood of redevelopment of hypophosphatemia over the following 2 days and supplementation should be given accordingly."
8 Rosen GH, Boullata JI, O'Rangers EA, Enow NB, Shin B.  Department of Pharmacy, University of Maryland Medical System, Baltimore, USA. Intravenous phosphate repletion regimen for critically ill patients with moderate hypophosphatemia. Crit Care Med 1995 Jul;23(7):1204-10 
9 Schwartz A, Gurman G, Cohen G, Gilutz H, Brill S, Schily M, Gurevitch B, Shoenfeld Y. Association between hypophosphatemia and cardiac arrhythmias in the early stages of sepsis. Eur J Intern Med 2002 Oct;13(7):434. 
10 Shiber JR, Mattu A. Serum phosphate abnormalities in the emergency department. J Emerg Med. 2002 Nov;23(4):395-400. 
"Patients with severe or symptomatic hypophosphatemia should be treated with IV phosphate therapy (0.08-0.16 mg/kg over 6 h) and admitted for monitoring and subsequent serum electrolyte testing."
11 Subramanian, R, Khardori, R. Severe hypophosphatemia. Medicine 2000; 79:1. 
12 Wilson HK, Keuer SP, Lea AS, Boyd AE 3rd, Eknoyan G. Phosphate therapy in diabetic ketoacidosis. Arch Intern Med 1982 Mar;142(3):517-20
13 Zazzo JF, Troche G, Ruel P, Maintenant J. High incidence of hypophosphatemia in surgical intensive care patients: efficacy of phosphorus therapy on myocardial function. ntensive Care Med 1995 Oct;21(10):826-31.

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