K-Phos Original (potassium phosphate,monobasic)
Phosphates Oral Tablet, Soluble
Last reviewed · Source: First Databank (FDB) drug data
Overview
Laxatives containing magnesium cations or phosphate anions are commonly termed saline laxatives.
USES: This medication helps control the amount of calcium in the body and urine. It works by making the urine more acidic. It is used to prevent calcium kidney stones.
It is also used to decrease the amount of ammonia in urine, thereby reducing odor and skin irritation caused by high-ammonia urine. This medication is also given to help certain antibiotics for bladder infections (such as methenamine) work better.
Generic name: potassium phosphate,monobasic
Pronunciation: (poh-TASS-ee-um ACID FOSS-fate)
Drug class: Phosphates
Therapeutic class: Genitourinary Therapy
Reference product & biosimilars
No reference, biosimilar or interchangeable associated with this drug.
Today’s intelligence on K-Phos Original
Indications
The following indications are listed for K-Phos Original:
- Hypophosphatemia
Also known as: Abnormally Decreased Blood Phosphate Level.
Dosing
Saline laxatives should be administered only at infrequent intervals. Most studies suggest that the minimum effective oral laxative dose of magnesium is 80 mEq. The usual dosages of the various saline laxatives are below; for dosages in children younger than the ages listed, a physician should be consulted.
For precautions that should be considered before administration of saline laxatives in patients susceptible to adverse effects, see Cautions: Saline Laxatives, in the Cathartics and Laxatives General Statement 56:12.
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Drug interactions
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Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.
Oral Phosphates; Active Vitamin D Analogs/Burosumab
SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.
MECHANISM OF ACTION: Both burosumab and phosphates or vitamin D may increase serum phosphate levels. This combination may lead to greater increases in serum phosphate than anticipated.
CLINICAL EFFECTS: The combination of burosumab with oral phosphates or active vitamin D analogs may result in hyperphosphatemia and may increase the risk of nephrocalcinosis.(1)
PREDISPOSING FACTORS: Patients with renal impairment have alterations in mineral metabolism that may increase the risk of hyperphosphatemia.(1)
PATIENT MANAGEMENT: The concomitant use of burosumab with oral phosphates or active vitamin D analogs is contraindicated. Discontinue oral phosphate and/or active vitamin D analogs one week before starting burosumab.(1)
DISCUSSION: Burosumab restores dysfunctional renal phosphate reabsorption and renal production of 1,25-dihydroxyvitamin D to treat X-linked hypophosphatemia. Additional oral phosphates and/or active vitamin D analogs may raise serum phosphate higher than anticipated.
Urinary Alkalinizers/Methenamine
SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.
MECHANISM OF ACTION: Urinary alkalinizers may elevate urinary ph preventing the conversion of methenamine to formaldehyde and mandelic acid.(1)
CLINICAL EFFECTS: Concurrent administration may result in alkalinization of the urine causing methenamine to be less effective.(1)
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: The Australian and UK manufacturers of methenamine state that concurrent use with agents that make urine alkaline or urine alkalinizing agents should be avoided.(2,3) Patients receiving concurrent therapy should be monitored for urinary ph and any worsening symptoms of their infection, including dysuria, flank pain, or fever.(1)
DISCUSSION: Administration of urinary alkalinizers may result in alkalinization of the urine resulting in therapeutic failure of methenamine. Formaldehyde is released by acid hydrolysis from methenamine resulting in bactericidal concentrations at urinary ph 5.0 to 5.5. Above urinary ph 6.0 there is insufficient quantities of formaldehyde and methenamine released to achieve a therapeutic response.(1) An in vitro study showed that methenamine efficacy is achieved when the urine pH is less than 5.7 to 5.85.(4)
Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
Oral Phosphate Supplements; Urinary Ph Modifiers/Alum;Ca;Mag
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Medications containing significant amounts of aluminum, calcium, or magnesium may bind to the phosphate and prevent its absorption.(1)
CLINICAL EFFECTS: Concurrent use of medications containing significant amounts of aluminum, calcium, or magnesium may result in decreased effectiveness of phosphate supplements and urinary pH modifiers high in phosphate.(1)
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: Patients receiving phosphate supplements or urinary pH modifiers high in phosphate should be instructed to avoid medications containing aluminum, calcium, or magnesium.(1) If concurrent use cannot be avoided, separate the administration of phosphate containing products by as much time as possible from medications containing aluminum, calcium, or magnesium. Some phosphate laxative products used as phosphate supplements may contain sufficient quantities of phosphate to interact as well.
DISCUSSION: The manufacturer of K-Phos states that products containing aluminum, calcium, or magnesium may bind to the phosphate and prevent its absorption. Therefore, patients receiving phosphate supplements and urinary pH modifiers high in phosphate should be instructed to avoid products containing aluminum, calcium, or magnesium.(1)
Phosphate Supplements;Urine Ph Modifiers/Phosphate Reducers
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Lanthanum and sevelamer bind to phosphate.(1-2) Tenapanor is a sodium/hydrogen exchanger 3 (NHE3) inhibitor.(3) All three agents are used to lower phosphate absorption in the body.(1-3)
CLINICAL EFFECTS: Concurrent use of phosphate supplements or urinary pH modifiers high in phosphate with agents that reduce serum phosphorus may decrease the effectiveness of both agents.
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: Patients should normally not receive phosphate supplements or urinary pH modifiers high in phosphate concurrently with agents that reduce serum phosphorus.
DISCUSSION: Lanthanum, sevelamer, and tenapanor are indicated to control phosphorus levels. Consider discontinuing or holding phosphate supplements and urinary pH modifiers high in phosphate in patients receiving these agents.
Potassium Supplements/Eplerenone
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Eplerenone increases serum potassium levels.(1)
CLINICAL EFFECTS: Concurrent use of eplerenone with a potassium supplement may result in hyperkalemia.(1)
PREDISPOSING FACTORS: Renal impairment.
PATIENT MANAGEMENT: The manufacturer of eplerenone states that the use of eplerenone for the treatment of hypertension in patients receiving potassium supplements is contraindicated.(1)
DISCUSSION: The main risk of eplerenone therapy is hyperkalemia. The risk of hyperkalemia can be reduced by avoiding potassium supplements during eplerenone therapy.(1)
Potassium Supplements/Potassium Binders
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Patiromer, sodium polystyrene sulfonate and sodium zirconium cyclosilicate bind to potassium.(1-3)
CLINICAL EFFECTS: Concurrent use of potassium supplements and patiromer, sodium polystyrene sulfonate or sodium zirconium cyclosilicate may decrease the effectiveness of both agents.
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: Patients should normally not receive potassium supplements and patiromer, sodium polystyrene sulfonate or sodium zirconium cyclosilicate concurrently.(1-3) Patiromer, sodium polystyrene sulfonate or sodium zirconium cyclosilicate are indicated for management of hyperkalemia. Consider discontinuing or holding potassium supplements in patients who develop hyperkalemia requiring treatment.
DISCUSSION: Patiromer, sodium polystyrene sulfonate and sodium zirconium cyclosilicate are indicated for hyperkalemia. Consider discontinuing or holding potassium supplements in patients receiving sodium polystyrene sulfonate or sodium zirconium cyclosilicate.
Potassium Supplements/Potassium Sparing Diuretics
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Decreased renal excretion of potassium, resulting from administration of a potassium sparing diuretic.
CLINICAL EFFECTS: May observe hyperkalemia which may be severe or even fatal.
PREDISPOSING FACTORS: Renal function impairment.
PATIENT MANAGEMENT: If both drugs are administered, monitor potassium levels. Adjust the dose of the drugs accordingly. This combination should probably be avoided if possible.
DISCUSSION: The interaction is well documented. Patients with decreased renal function are especially at risk of developing hyperkalemia from this drug combination. A commonly held belief is that a potassium sparing diuretic formulated in combination with a thiazide diuretic, such as Dyazide, will not exhibit this interaction. Although the likelihood of hyperkalemia occurring may be reduced somewhat, a danger still exists.
Potassium Supplements/Trimethoprim
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Trimethoprim may increase serum potassium levels by reduction in potassium elimination.(1-3) The combination of trimethoprim and potassium supplements can have an additive effect on serum potassium resulting in potentially dangerous levels.
CLINICAL EFFECTS: Concurrent use of trimethoprim and potassium supplements may result in hyperkalemia, which may be severe.
PREDISPOSING FACTORS: Patients who are elderly, have any degree of renal insufficiency or heart failure have an increased risk for hyperkalemia.(1-9) Concomitant use with other drugs associated with hyperkalemia risk (e.g. ACE Inhibitors, angiotensin II receptor antagonists, aldosterone antagonists, NSAIDs) and high doses of trimethoprim further increase the risk for hyperkalemia.(1-8) Interaction risk and severity is greater in patients with multiple risk factors.
PATIENT MANAGEMENT: Assure adequate monitoring for hyperkalemia.(1-9) Patients receiving trimethoprim and a potassium supplement concurrently should have their serum potassium monitored at baseline and during treatment. Potassium supplementation may need to be held during antibiotic therapy, especially when other predisposing factors for hyperkalemia are present. Peak potassium increase due to trimethoprim is delayed and generally occurs after 4 or more days of therapy.(3,5,6) When possible, alternative antibiotic therapy should be considered in patients with one or more risk factors for hyperkalemia, e.g. renal impairment, heart failure, age > 65 years, and/or receiving additional meds associated with hyperkalemia risk (e.g. ACE inhibitors, angiotensin II receptor blockers, aldosterone antagonists, NSAIDs).(6)
DISCUSSION: A nested case-control study evaluated the risk for hyperkalemia in 19,194 patients with newly diagnosed heart failure. Over a mean follow-up of 3.9 years 2,176 cases of hyperkalemia (96.7% with a potassium value of => 5.5 mmol/L) were identified. Study authors found that trimethoprim independently increased the risk for hyperkalemia (OR 2.82; 95% CI 1.88-4.23).(4) A retrospective cohort study evaluated the risk for hospitalization due to hyperkalemia in 393,039 elderly women (age >65 years) treated for a urinary tract infection (UTI) with trimethoprim-sulfamethoxazole (TMP-SMX) or another antibiotic (amoxicillin, ciprofloxacin, norfloxacin, nitrofurantoin). Baseline renal function was similar in all five antibiotic groups. When compared with amoxicillin, TMP-SMX use was associated with a 3.3-fold increased risk for hospitalization due to hyperkalemia. Ciprofloxacin, norfloxacin, and nitrofurantoin were not associated with a risk for hyperkalemia.(9) A prospective study of hospitalized patients evaluated the risk for hyperkalemia in patients who received standard dose TMP-SMX (<= 320 mg trimethoprim, <= 1600 mg sulfamethoxazole daily) versus a control group who received a different antibiotic for at least 5 days. The two groups were similar in age, renal function and use of potassium altering medications. Serum potassium concentration increased in TMP-SMX patients by 1.21 mmol/L (CI 1.09 - 1.32 mmol/L), a change which was statistically significant in patients with a pretreatment serum creatinine = or > 1.2. In control patients, serum potassium decreased during antibiotic therapy (change not quantitated by authors).(5)
Serum Phosphate Level-Altering Drugs/Erdafitinib
SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.
MECHANISM OF ACTION: Medications that alter serum phosphate may interfere with interpretation of phosphate levels that are needed to determine initial erdafitinib dose.(1)
CLINICAL EFFECTS: Serum phosphate levels that are elevated by concomitant medications may result in an inappropriately low dose and decreased effectiveness of erdafitinib. Serum phosphate levels that are decreased by concomitant medications may result in an inappropriately high dose and increased toxicity from erdafitinib.
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: The manufacturer of erdafitinib states that agents that alter serum phosphate levels should be avoided before the initial dose increase period for erdafitinib based on serum phosphate levels (days 14 to 21).(1)
DISCUSSION: Concomitant administration of serum phosphate level-altering agents during the initial dose increase period of erdafitinib based on serum phosphate levels (days 14 to 21) may interfere with serum phospate levels and lead to incorrect dosing of erdafitinib.(1) Agents that may alter serum phosphate levels linked to this monograph include: aluminum carbonate, aluminum hydroxide, calcium acetate, calcium carbonate, calcium citrate, cod liver oil, ferric citrate, lanthanum, magnesium carbonate, magnesium hydroxide, potassium phosphate, sevelamer, sodium phosphate, sucroferric oxyhydroxide, tenapanor, and vitamin D.(1)
Moderate Interaction: Assess the risk to the patient and take action as needed.
Agents That Increase Potassium/Baxdrostat
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: The combination of baxdrostat and agents that increase potassium such as aldosterone receptor antagonists, potassium-sparing diuretics, and potassium supplements can have an additive effect on serum potassium levels.
CLINICAL EFFECTS: Concurrent use of baxdrostat and agents that increase potassium may result in hyperkalemia, which may be severe.
PREDISPOSING FACTORS: More frequent monitoring is recommended for patients at increased risk of hyperkalemia (e.g., patients greater than or equal to 65 years or age, those with diabetes mellitus or chronic kidney disease).(1)
PATIENT MANAGEMENT: The manufacturer of baxdrostat states concurrent use with medications that may increase potassium warrants more frequent monitoring of serum potassium.(1) Assess serum potassium prior to initiation of baxdrostat and monitor periodically during treatment. Correct serum potassium abnormalities prior to initiation of baxdrostat.(1) If hyperkalemia occurs, treat hyperkalemia and consider interrupting or discontinuing baxdrostat. Consider more frequent monitoring of serum potassium in patients who restart baxdrostat after experiencing hyperkalemia. Permanently discontinue baxdrostat if clinically significant hyperkalemia recurs.(1)
DISCUSSION: Baxdrostat may increase potassium. Concurrent use with aldosterone receptor antagonists, potassium-sparing diuretics, and potassium supplements may have additive effects on serum potassium levels, resulting in hyperkalemia. The risk of hyperkalemia can be reduced by monitoring serum potassium more frequently when baxdrostat is administered concomitantly with these agents.
Potassium Supplements/Aliskiren
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: Aliskiren may decrease the renal excretion of potassium.
CLINICAL EFFECTS: Concurrent use of potassium supplements with aliskiren may result in hyperkalemia.
PREDISPOSING FACTORS: Impaired renal function; diabetes mellitus.
PATIENT MANAGEMENT: Monitor serum potassium and adjust the dosage accordingly in patients receiving concurrent therapy with potassium supplements and aliskiren.
DISCUSSION: Several studies have indicated that serum potassium levels increase when ACE inhibitors and ARB therapy is initiated and decrease when the drug is lowered. Increased potassium levels have also been seen with aliskiren. Based on this data, serum potassium levels should be monitored in patients receiving potassium supplements with aliskiren.
Potassium Supplements/Angiotensin Ii Receptor Blocker (Arb)
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: Angiotensin II receptor blockers (ARBs) may decrease the renal excretion of potassium.
CLINICAL EFFECTS: Concurrent use of potassium supplements with ARBs may result in hyperkalemia.
PREDISPOSING FACTORS: Impaired renal function; diabetes mellitus.
PATIENT MANAGEMENT: Monitor serum potassium and adjust the dosage accordingly in patients receiving concurrent therapy with potassium supplements and ARBs.
DISCUSSION: Several studies have indicated that serum potassium levels increase when ARB therapy is initiated and decrease when the drug is lowered. Based on this data, serum potassium levels should be monitored in patients receiving potassium supplements with ARBs.
Potassium Supplements/Drospirenone
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: Drospirenone has antimineralocorticoid activity and may cause hyperkalemia. Potassium supplements also increase potassium levels.(1)
CLINICAL EFFECTS: Concurrent use of drospirenone and potassium supplements may result in hyperkalemia.(1)
PREDISPOSING FACTORS: Renal insufficiency, hepatic dysfunction, adrenal insufficiency, and use of potassium-sparing diuretics, ACE inhibitors, angiotensin II receptor antagonists, heparin, and NSAIDs may increase potassium levels.(1)
PATIENT MANAGEMENT: Patients receiving drospirenone with a potassium supplement should have their serum potassium level checked during the first treatment cycle.(1)
DISCUSSION: Drospirenone has antimineralocorticoid activity comparable to 25 mg of spironolactone and may result in hyperkalemia. Concurrent use of potassium-supplements also increase potassium levels.(1)
Potassium Supplements/Selected Ace Inhibitors
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed. SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: ACE inhibitors may decrease the renal excretion of potassium. MECHANISM OF ACTION: ACE inhibitors may decrease the renal excretion of potassium.
CLINICAL EFFECTS: Concurrent use of potassium supplements with ACE inhibitors may result in hyperkalemia. CLINICAL EFFECTS: Concurrent use of potassium supplements with ACE inhibitors may result in hyperkalemia.
PREDISPOSING FACTORS: Impaired renal function; diabetes mellitus. PREDISPOSING FACTORS: Impaired renal function; diabetes mellitus.
PATIENT MANAGEMENT: Monitor serum potassium and adjust the dosage accordingly in patients receiving concurrent therapy with potassium supplements and ACE inhibitors. PATIENT MANAGEMENT: Monitor serum potassium and adjust the dosage accordingly in patients receiving concurrent therapy with potassium supplements and ACE inhibitors.
DISCUSSION: Several studies have indicated that serum potassium levels increase when ACE inhibitors is initiated and decrease when the drug is lowered. Based on this data, serum potassium levels should be monitored in patients receiving potassium supplements with ACE inhibitors. Selected ACE inhibitors linked to this monograph include: alacepril, cilazapril, delapril, imidapril, perindopril, spirapril, temocapril, and zofenopril. DISCUSSION: Several studies have indicated that serum potassium levels increase when ACE inhibitors is initiated and decrease when the drug is lowered. Based on this data, serum potassium levels should be monitored in patients receiving potassium supplements with ACE inhibitors. Selected ACE inhibitors linked to this monograph include: benazepril, captopril, enalapril, fosinopril, lisinopril, moexipril, quinapril, ramipril, and trandolapril.
Urinary Alkalinizers/Memantine; Amantadine
SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.
MECHANISM OF ACTION: Memantine and amantadine elimination is impaired by urinary alkalinization.(1,2)
CLINICAL EFFECTS: Potentiation of memantine or amantadine effects may be observed.
PREDISPOSING FACTORS: None determined.
PATIENT MANAGEMENT: Monitor patient for adverse reactions such as dizziness, headache, or confusion if a urinary alkalinizer is required. The memantine or amantadine dose may need to be adjusted when a urinary alkalinizer is started or stopped.(1,2)
DISCUSSION: The clearance of memantine was reduced by about 80% under alkaline urine conditions at pH 8. Urine alkalinization may lead to an accumulation of memantine with a possible increase in adverse effects. Urine pH is also altered by diet and clinical state of the patient (e.g., renal tubular acidosis or severe infections of the urinary tract). Hence, memantine should be used with caution under these conditions.(1) A study in rats showed that concomitant administration of sodium bicarbonate with amantadine caused a decrease in amantadine renal clearance (1.16 vs. 0.76). Amantadine's area-under-the-curve (AUC) was increased approximately 78%.(3) A study in 12 healthy subjects showed that plasma concentrations of memantine are dependent on urine pH. Alkaline urine pH caused a 79% reduction in renal clearance.(4)
Contraindications
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- Hyperphosphatemia
- Anuria
- Azotemia
- Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
- Chronic kidney disease stage 5 (failure) GFr<15 ml/min
- Dehydration
- Hyporeninemic hypoaldosteronism
- Myotonia congenita - autosomal dominant form
- Kidney disease with likely reduction in glomerular filtration rate (GFr)
Adverse reactions
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Rare or Very Rare
- Acute renal failure
- Body fluid retention
- Cardiac arrhythmia
- Hyperkalemia
- Hypernatremia
- Hyperphosphatemia
- Hypocalcemic tetany
- Hypovolemia
- Ischemic colitis
- Nephrocalcinosis
- Renal failure
- Seizure disorder
- Unconsciousness
Less Frequent
- Abdominal pain with cramps
- Diarrhea
- Nausea
- Vomiting
Precautions
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ICD codes
| Code | Type | Description |
|---|---|---|
| Hypophosphatemia | ||
| E83.31 | ICD10CM | Familial hypophosphatemia |
ICD code information from First Databank (FDB).
Formulary status
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Last reviewed · Source: First Databank (FDB) drug data
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