What is the treatment for itching caused by hyperphosphatemia in patients undergoing dialysis?

Treatment of Itching Caused by Hyperphosphatemia in Dialysis Patients

For dialysis patients with itching related to hyperphosphatemia, first optimize dialysis adequacy (target Kt/V ~1.6), normalize calcium-phosphate balance, control PTH levels, correct anemia with erythropoietin, and use emollients before escalating to specific anti-pruritic therapies. 1

Step 1: Control Hyperphosphatemia

Dietary Phosphorus Restriction

• Restrict dietary phosphorus to 800-1,000 mg/day (adjusted for dietary protein needs) when serum phosphorus exceeds 5.5 mg/dL in dialysis patients 2
• Focus patient education on phosphate bioavailability: animal-based phosphate (40-60% absorbed) versus plant-based phosphate (20-50% absorbed), and avoid processed foods containing inorganic phosphate additives which are nearly 100% absorbed 2
• Monitor serum phosphorus monthly following dietary restriction 2

Phosphate Binder Selection

When dietary restriction fails to maintain phosphorus between 3.5-5.5 mg/dL, prescribe phosphate binders based on the following algorithm: 2

First-Line Binder Choice:

• For patients with normal calcium levels (8.4-9.5 mg/dL) and PTH >150 pg/mL: Either calcium-based binders OR non-calcium binders (sevelamer, lanthanum) may be used 2
• Limit elemental calcium from binders to ≤1,500 mg/day, with total calcium intake (including dietary) ≤2,000 mg/day 2

Mandatory Non-Calcium Binder Situations:

• Hypercalcemia (corrected calcium >10.2 mg/dL): Use sevelamer or lanthanum carbonate exclusively 2
• Low PTH (<150 pg/mL on 2 consecutive measurements): Avoid calcium-based binders 2
• Severe vascular or soft-tissue calcifications: Prefer non-calcium binders 2

Combination Therapy:

• If phosphorus remains >5.5 mg/dL despite monotherapy with either calcium-based or non-calcium binders, combine both types 2

Severe Hyperphosphatemia (>7.0 mg/dL):

• Aluminum-based binders may be used for short-term only (maximum 4 weeks, one course only), then switch to other binders 2
• Consider more frequent dialysis 2

Step 2: Optimize Dialysis Parameters

• Ensure adequate dialysis with target Kt/V of approximately 1.6, as pruritus is more common in underdialyzed patients 1
• Verify dialysis adequacy before attributing itching solely to hyperphosphatemia 1

Step 3: Address Uremic Pruritus Directly

First-Line Anti-Pruritic Measures:

• Apply emollients regularly to address xerosis (dry skin), the most common cutaneous manifestation in dialysis patients that lowers the itch threshold 1
• Normalize calcium-phosphate balance and control PTH to accepted levels, as secondary/tertiary hyperparathyroidism contributes to pruritus 1
• Correct anemia with erythropoietin if present 1

Pharmacologic Treatment for Persistent Pruritus:

If itching persists despite optimized phosphate control:

• Gabapentin 100-300 mg after each dialysis session (three times weekly) is the most effective medication for uremic pruritus, with significantly lower doses required than non-ESRD populations due to reduced renal clearance 1
• Topical capsaicin 0.025% cream applied four times daily to affected areas provides marked relief in most patients (14 of 17 patients in trials reported marked relief, 5 achieved complete remission) 1

Alternative Therapies:

• Broad-band UVB (BB-UVB) phototherapy is effective for many patients with uremic pruritus 1
• Topical doxepin may be considered for severe cases, but strictly limit to 8 days, 10% body surface area, and maximum 12 g daily 1

Critical Pitfalls to Avoid

• Do NOT use cetirizine for uremic pruritus - it has been proven ineffective specifically for this condition despite efficacy in other pruritic conditions 1
• Avoid long-term sedative antihistamines (except in palliative care) as they may predispose to dementia 1
• Do NOT prescribe calcium-based binders when corrected calcium >10.2 mg/dL - this will worsen hypercalcemia and potentially increase vascular calcification 2
• Avoid excessive calcium loading - studies show progression of coronary and aortic calcification with high-dose calcium-based binders, particularly calcium acetate 2

Monitoring Strategy

• Check serum phosphorus monthly during treatment adjustments 2
• Monitor corrected total calcium to maintain 8.4-9.5 mg/dL (lower end of normal range preferred in dialysis patients) 2
• Assess pruritus intensity at each dialysis session to determine treatment response 1
• If phosphorus control is achieved but itching persists, escalate to gabapentin or phototherapy rather than further intensifying phosphate binders 1