potassium acid phosphate

High Alert

Adjunct therapy of urinary tract infections with methenamine hippurate or mandelate.
Prevention of calcium urinary stones.

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hyperkalemia;
Hyperphosphatemia;
Hypocalcemia;
Hypomagnesemia;
Severe renal impairment.

Use Cautiously in:

Metabolic alkalosis;
Cardiac disease;
Renal impairment;
Children (safety and effectiveness not established).

Adv. Reactions/Side Effects ⬆ ⬇

Related to hyperphosphatemia, unless otherwise indicated

CV: ARRHYTHMIAS, CARDIAC ARREST, ECG changes (absent P waves, widening of the QRS complex with biphasic curve), hypotension, hyperkalemiaARRHYTHMIAS, bradycardia, ECG changes (prolonged PR interval, ST segment depression, peaked T waves)

GI: abdominal pain, diarrhea, flatulence, nausea, vomiting

F and E: hyperkalemia, hyperphosphatemia, hypocalcemia, hypomagnesemia

MS: muscle cramps, tremors

Neuro: flaccid paralysis, heaviness of legs, paresthesias, confusion, listlessness, weakness

Interactions ⬆ ⬇

Drug-drug:

Concurrent use of potassium-sparing diuretics,ACE inhibitors, angiotensin receptor blockers, or aldosterone antagonists may result in hyperkalemia.
Concurrent administration of calcium- or aluminum- containing compounds or sucralfate decreases absorption of phosphates by formation of insoluble complexes.

Drug-Food:

Oxalates (in berries, nuts, chocolate, beans, celery, and tomatoes) and phytates (in bran and whole grains) may decrease the absorption of phosphates by binding them in the GI tract.

Availability ⬆ ⬇

Tablets for oral solution: 500 mg (contains 3.7 mmol phosphorus)

Route/Dosage ⬆ ⬇

PO (Adults ): 1 g (7.4 mmol) in 6–8 oz of water 4 times daily with meals and at bedtime.

US Brand Names ⬆ ⬇

Action ⬆ ⬇

Serves as a buffer for the excretion of hydrogen ions by the kidney.
Dibasic potassium phosphate is converted in renal tubules to monobasic salt by hydrogen ions, resulting in urinary acidification.
Acidification of urine is required for methenamine hippurate or mandelate to be active as a urinary anti-infective.
Acidification of urine increases solubility of calcium, decreasing calcium stone formation.

Therapeutic effects:

Urinary acidification.
Increased efficacy of methenamine.
Decreased formation of calcium urinary tract stones.

Classifications ⬆ ⬇

Therapeutic Classification: antiurolithics

Pharmacokinetics ⬆ ⬇

Absorption: Well absorbed following oral administration.

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 ⬆ ⬇

ROUTE	ONSET	PEAK	DURATION
PO	unknown	unknown	unknown

Patient/Family Teaching ⬆ ⬇

Explain to patient purpose of the medication and the need to take as directed. If a dose is missed, it should be taken as soon as remembered unless within 1–2 hr of the next dose. Explain that the tablets should not be swallowed whole. Tablets should be dissolved in water.
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 report diarrhea, weakness, fatigue, muscle cramps, or tremors promptly.

section name header

Indications ⬇