potassium and sodium phosphates

REMS

Treatment and prevention of phosphate depletion in patients who are unable to ingest adequate dietary phosphate.
Adjunct therapy of urinary tract infections with methenamine.
Prevention of calcium urinary stones.
Phosphate salts of potassium may be used in hypokalemic patients with metabolic acidosis or coexisting phosphorus deficiency.

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hyperkalemia (potassium salts);
Hyperphosphatemia;
Hypocalcemia;
Severe renal impairment;
Untreated Addison’s disease (potassium salts).

Use Cautiously in:

Hyperparathyroidism;
Cardiac disease;
Hypernatremia (sodium phosphate only);
Hypertension (sodium phosphate only);
Mild or moderate renal impairment.

Adv. Reactions/Side Effects ⬆ ⬇

Related to hyperphosphatemia, unless otherwise indicated

CV: ARRHYTHMIAS, bradycardia, CARDIAC ARREST, ECG changes (absent P waves, widening of the QRS complex with biphasic curve, peaked T waves), edema

GI: diarrhea, abdominal pain, nausea, vomiting

F and E: hyperkalemia, hypernatremia, hyperphosphatemia, hypocalcemia, hypomagnesemia

MS: hypocalcemia, hyperkalemiamuscle cramps

Neuro: confusion, dizziness, flaccid paralysis, headache, heaviness of legs, paresthesias, tremor, weakness

Interactions ⬆ ⬇

Drug-drug:

Concurrent use of potassium-sparing diuretics, ACE inhibitors, or angiotensin II receptor blockers with potassium phosphate may result in hyperkalemia.
Concurrent use of corticosteroids with sodium phosphate may result in hypernatremia.
Concurrent administration of calcium-, magnesium-, or aluminum-containing compounds↓ absorption of phosphates by formation of insoluble complexes.
Vitamin D enhances the absorption of phosphates.

Drug-Food:

Oxalates (in spinach and rhubarb) and phytates (in bran and whole grains) may ↓ absorption of phosphates by binding them in the GI tract.

Availability ⬆ ⬇

Potassium and Sodium Phosphates

Tablets (K-Phos Neutral): elemental phosphorus 250 mg (8 mmol), sodium 298 mg (13 mEq), and potassium 45 mg (1.1 mEq)
Tablets (K-Phos No.2): elemental phosphorus 250 mg (8 mmol), sodium 134 mg (5.8 mEq), and potassium 88 mg (2.3 mEq)
Powder for oral solution: elemental phosphorus 250 mg (8 mmol), sodium 164 mg (7.1 mEq), and potassium 278 mg (7.1 mEq)/packet

Route/Dosage ⬆ ⬇

Phosphorous Supplementation

PO (Adults and Children >4 yr): 250–500 mg (8–16 mmol) phosphorus (1–2 packets) 4 times daily.
PO (Children <4 yr): 250 mg (8 mmol) phosphorus (1 packet) 4 times daily.

Urinary Acidification

PO (Adults ): 2 tablets 4 times/day.

Maintenance Phosphorus

PO (Adults ): 50–150 mmol/day in divided doses.
PO (Children ): 2–3 mmol/kg/day in divided doses.

US Brand Names ⬆ ⬇

K-Phos Neutral, K-Phos No. 2

Action ⬆ ⬇

Phosphate is present in bone and is involved in energy transfer and carbohydrate metabolism.
Serves as a buffer for the excretion of hydrogen ions by the kidneys.
Dibasic potassium phosphate is converted in renal tubule to monobasic salt, resulting in urinary acidification, which is required for methenamine hippurate or mandelate to be active as urinary anti-infectives.
Acidification of urine increases solubility of calcium, decreasing calcium stone formation.

Therapeutic effects:

Replacement of phosphorus in deficiency states.
Urinary acidification.
Increased efficacy of methenamine.
Decreased formation of calcium urinary tract stones.

Classifications ⬆ ⬇

Therapeutic Classification: antiurolithics, mineral and electrolyte replacements/supplements

Pharmacokinetics ⬆ ⬇

Absorption: Well absorbed following oral administration. Vitamin D promotes GI absorption of phosphates.

Distribution: Phosphates enter extracellular fluids and are then actively transported to sites of action.

Metabolism/Excretion: Excreted mainly (>90%) by the kidneys.

Half-Life: Unknown.

Time/Action Profile ⬆ ⬇

(effects on serum phosphate levels)

ROUTE	ONSET	PEAK	DURATION
PO	unknown	unknown	unknown

Patient/Family Teaching ⬆ ⬇

Explain to the patient the purpose of the medication and the need to take as directed. Take missed doses as soon as remembered unless within 1 or 2 hr of the next dose. Explain that the tablets should not be swallowed whole. Tablets should be dissolved in water.
Instruct patients in low-sodium diet (see Food Sources for Specific Nutrients).
Advise patient of the importance of maintaining a high fluid intake (drinking at least one 8-oz glass of water each hr) to prevent kidney stones.
Instruct the patient to promptly report diarrhea, weakness, fatigue, muscle cramps, unexplained weight gain, swelling of lower extremities, shortness of breath, unusual thirst, or tremors.

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Indications ⬇