What is the recommended approach for flush therapy in an adult patient with renal stones and no significant medical history?

Flush Therapy for Renal Stones

For adult patients with renal stones and no significant medical history, the primary "flush therapy" is aggressive fluid intake to achieve at least 2 liters of urine output daily, which serves as both first-line treatment and prevention of recurrence. 1, 2

Initial Fluid Management Strategy

Increase fluid intake spread throughout the day to achieve a minimum urine output of 2-2.5 liters daily. 1, 2, 3 This approach reduces stone recurrence by approximately 50% and represents the cornerstone of conservative management. 3

Specific Fluid Recommendations

• Water is the preferred beverage, though coffee, tea, beer, and wine also reduce stone formation risk 3
• Avoid grapefruit juice (increases stone risk by 40%), sugar-sweetened beverages, and colas acidified with phosphoric acid 3
• Mineral water versus tap water shows no significant difference in stone recurrence rates 1
• Do not rely on the "eight glasses per day" rule or urine color as guides—tailor recommendations using actual 24-hour urine volume data 3

When Fluid Therapy Alone Fails

If increased fluid intake fails to prevent stone recurrence, initiate pharmacologic monotherapy with one of the following agents based on metabolic profile: 1, 2

First-Line Pharmacologic Options

• Thiazide diuretics for hypercalciuria (>200 mg/day): hydrochlorothiazide 50 mg, chlorthalidone 25-50 mg, or indapamide 2.5 mg 1, 2
• Potassium citrate 30-100 mEq/day for hypocitraturia (<320 mg/day), targeting urinary pH 6.0-6.5 (not exceeding 7.0 to avoid calcium phosphate precipitation) 2, 3
• Allopurinol for hyperuricosuria (>800 mg/day in men, >750 mg/day in women) with normocalciuria 1, 2, 3

Important: Combination therapy with multiple agents has not been shown more beneficial than monotherapy. 1, 4

Dietary Modifications to Enhance Flush Therapy

• Maintain normal dietary calcium intake (1,000-1,200 mg/day)—do not restrict calcium 2, 4, 3
• Restrict dietary sodium to ≤2,300 mg/day 3
• Reduce animal protein to 5-7 servings of meat, fish, or poultry per week 3
• Increase fruits and vegetables to counterbalance acid load and raise urinary pH 3

Critical Caveats for Flush Therapy

Patients who already drink recommended fluid amounts or those with contraindications to increased fluid intake (e.g., heart failure, end-stage renal disease) should not be directed to increase fluids further. 1

Higher doses of thiazides are more effective but associated with more adverse effects—the effectiveness of lower doses in preventing stone recurrence is not well established. 1, 2

Monitoring Response to Flush Therapy

• Obtain 24-hour urine collection at 6 months to verify adequate urine volume (>2 liters/day) and assess metabolic parameters 3
• Measure urinary pH to ensure it remains between 6.0-6.5 and does not exceed 7.0 3
• Monitor stone recurrence with imaging as clinically indicated 3

When Flush Therapy Is Insufficient

For symptomatic stones ≤20 mm that fail conservative management, offer shock wave lithotripsy (SWL) or ureteroscopy (URS). 1 For stones >20 mm, percutaneous nephrolithotomy (PCNL) should be offered as first-line surgical therapy. 1

In patients with obstructing stones and suspected infection, urgent drainage with nephrostomy tube or ureteral stent is mandatory before definitive stone treatment. 1