This is a presentation I gave with my colleague Pascal at the National Kidney Foundation Spring Clinical Meeting on 12 April 2025. For the full list of presentation summaries – click here.
Speakers: Pascale Khairallah MD, Kelly Picard PhD RD
Objectives:
- Articulate factors to consider when determining patient-specific phosphorus goals
- Recall pertinent clinical pearls and counseling points for phosphate lowering pharmacotherapy
- Apply contemporary literature and evidence to a patient case scenario involving phosphate management
Why Does Serum Phosphorus Matter?
High serum phosphorus is linked with increased mortality, vascular calcification, and bone disease. The association is strong, but there is little direct evidence showing that lowering phosphorus improves patient outcomes.
One major trial — the PHOSPHATE trial — aims to answer this question. It is randomizing patients to either strict or liberalized phosphorus targets and tracking cardiovascular events, mortality, and quality of life.
What Targets are Clinicians Using?
In our live poll, most clinicians aimed for 5.5–6.0 mg/dL (1.78–1.92 mmol/L). This matches findings from a Journal of Renal Nutrition survey, where most dietitians also used this range.
What do Guidelines say?
The 2020 KDOQI guidelines recommend targeting the laboratory’s upper limit of normal for serum phosphorus. This is typically lower than the targets most clinicians use.
Why the Gap Between Guidelines and Practice?
Our audience cited:
- Dietary challenges
- Patient adherence as the top barrier
- Pill burden
- Limited effectiveness of current treatments
Why Is It So Hard to Reach Target?
As shown in research I’ve covered before, dietary phosphorus intake often far exceeds what can be removed by dialysis or binders.
Other challenges:
- Phosphorus content is especially high in processed foods containing additives
- Limited phosphorus data on food labels
Shifting Dietary Strategies
Traditional low-phosphorus diets restricted nuts, seeds, pulses, whole grains, and dairy. We now avoid these broad restrictions because:
- They reduce important nutrients like fiber and calcium, both crucial for gut and bone health.
- Minimally processed plant foods have lower phosphorus bioavailability.
- Processed foods — not whole foods — contribute the most to phosphorus intake.
Examples of high-additive foods to limit:
- Chocolate bars
- Ready-to-eat or frozen meals
- Chips, crackers, granola bars
Phosphorus Binders: Old Challenges
Can add up to 19 tablets/day
Bind only 40–130 mg phosphorus per tablet vs ~2100–2500 mg daily intake
Work by binding phosphorus in the small intestine to reduce absorption
Most effective when taken just before meals
Phosphorus Blockers: Novel Agents
Tenapanor works differently from binders. It blocks sodium-hydrogen exchangers in the gut, reducing absorption of both sodium and phosphorus.
Advantages:
- Does not need to be taken with meals
- Can lower pill burden when used with binders
Considerations:
Recommended to avoid dosing right before dialysis
Main side effect is diarrhea
How effective is tenapenor?
Five key studies show phosphorus reductions of 0.2–0.61 mmol/L (0.65–2.0 mg/dL).
One study found patients reduced their binder count from 9 to 4 tablets/day while maintaining phosphorus control.
Availability
- Not approved for use as a phosphorus blocker in Canada, it is approved for use as a medication to treat IBS
- In the U.S., approved as an add-on therapy for those not tolerating binders or needing more control
- Dispensed from a central pharmacy, not community pharmacies
Take Aways:
- Hard outcome data to support that lowering serum phosphorus levels is associated with improved patient outcomes isn’t yet available. However the association between higher serum phosphate and worse patient outcomes is well-established.
- Dietary guidance is shifting toward targeting processed foods with additives, rather than restricting nutrient-rich whole foods.
- Tenapanor offers a novel mechanism and may help reduce pill burden when combined with binders.
Phosphorus Management at a Glance
? Why It Matters
- High serum phosphorus is linked to mortality, vascular calcification, and bone disease.
- No definitive trial yet proves that lowering phosphorus improves outcomes — results awaited from the PHOSPHATE trial.
? Targets
- Most clinicians/dietitians: 5.5–6.0 mg/dL (1.78–1.92 mmol/L)
- 2020 KDOQI guideline: Lab upper limit of normal
? Challenges
- Intake exceeds what dialysis + binders can remove
- Phosphorus not always labeled on foods
- Pill burden and binder tolerance issues
? Diet Strategy Shift
✅ Focus on limiting processed foods with phosphorus additives:
- Chocolate bars
- Frozen meals, ready-to-eat foods
- Chips, crackers, granola bars
❌ Avoid broad restriction of healthy plant foods — bioavailability is lower and they contain valuable nutrients
? Medications
Binders
- Example: calcium acetate, sevelamer
- Take just before meals
- Bind ~40–130 mg phosphorus per tablet
Blockers (Tenapanor)
- Reduces absorption via sodium-hydrogen exchanger inhibition
- Doesn’t need to be taken with meals
- Side effect: diarrhea
- May lower binder pill count
? Takeaway Message
Combine targeted diet changes with effective medication strategies to improve phosphorus control while minimizing pill burden.
