What is the medical management of renal stones?

Medical Management of Renal Stones

The cornerstone of renal stone management is increasing fluid intake to achieve at least 2.5 liters of urine output daily, combined with stone-type-specific pharmacological therapy: thiazide diuretics for calcium stones with hypercalciuria, potassium citrate for uric acid stones (targeting pH 6.0) and hypocitraturic calcium stones, and urinary alkalinization plus cystine-binding thiol drugs for cystine stones. 1, 2

Initial Diagnostic Workup

Stone analysis is mandatory when a stone is available, as composition directly determines treatment strategy 1, 2. The most common types are calcium oxalate (61%), calcium phosphate (15%), and uric acid (12%) 3.

Metabolic evaluation with 24-hour urine collection should be performed in all recurrent stone formers and high-risk first-time formers, analyzing total volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine 4, 1, 2. Obtain serum intact parathyroid hormone if primary hyperparathyroidism is suspected 1, 2.

Universal Dietary Interventions

Fluid intake is the single most important intervention across all stone types 2:

• Target minimum 2.5 liters of urine output daily for most stone types 1, 2
• For cystine stones, target at least 4 liters daily to decrease urinary cystine concentration below 250 mg/L 1, 2

Dietary modifications for calcium stones 1, 2:

• Maintain normal dietary calcium intake of 1,000-1,200 mg daily (do not restrict calcium, as this paradoxically increases oxalate absorption) 1
• Limit sodium to ≤2,300 mg daily 1, 2, 5
• Consume ample fruits and vegetables to counterbalance acid load 1

For cystine stones, restrict sodium and protein intake in addition to aggressive hydration 1, 2

Stone-Type-Specific Pharmacological Management

Calcium Stones

For hypercalciuria (most common metabolic abnormality):

• Thiazide diuretics are first-line therapy, combined with continued dietary sodium restriction to maximize hypocalciuric effect 1, 2
• Thiazides may be combined with potassium citrate when other metabolic abnormalities persist 1

For hypocitraturia:

• Potassium citrate therapy increases urinary citrate, a potent inhibitor of calcium stone crystallization 1, 2
• Potassium citrate is preferred over sodium citrate because sodium load increases urinary calcium excretion 1, 5

For hyperuricosuria (>800 mg/day in men, >750 mg/day in women) with normal urinary calcium:

• Allopurinol is recommended 1

For calcium phosphate stones:

• Exercise caution with excessive alkalinization, as calcium phosphate solubility decreases at higher pH 1
• Potassium citrate may be used if hypocitraturia is present 1

Uric Acid Stones

Potassium citrate is first-line therapy, not allopurinol 4, 5:

• Target urinary pH of 6.0 (range 6.0-6.8) to enhance uric acid solubility and achieve stone dissolution 5
• Most patients have low urinary pH rather than hyperuricosuria as the predominant risk factor 4, 5

Allopurinol should NOT be routinely offered as first-line therapy 4, 5:

• Reserve for documented hyperuricosuria (>800 mg/day in men, >750 mg/day in women) or persistent stone formation despite adequate urinary alkalinization 5

Sodium bicarbonate is a viable alternative to potassium citrate, but avoid sodium citrate due to increased urinary calcium excretion 5

Cystine Stones

First-line therapy includes 4, 2:

• Increased fluid intake (≥4 liters daily) 1, 2
• Restriction of sodium and protein intake 4, 2
• Urinary alkalinization with potassium citrate to raise pH to 7.0 4, 2

Second-line therapy:

• Tiopronin (alpha-mercaptopropionylglycine) for patients unresponsive to dietary modifications and urinary alkalinization, or with large recurrent stone burdens 4, 2
• Tiopronin is more effective and has fewer adverse events than d-penicillamine 4

Struvite Stones

Acetohydroxamic acid (AHA), a urease inhibitor, may be beneficial in patients at high risk for recurrence when surgical stone removal is not feasible, though extensive side effects may limit use 4, 1. Monitor patients with struvite stones for reinfection 4.

Follow-Up Monitoring Protocol

Initial follow-up (within 6 months):

• Obtain 24-hour urine specimen to assess response to dietary and/or medical therapy 4, 1, 2, 5
• For potassium citrate therapy, check serum potassium within 1-2 months 5

Ongoing monitoring:

• Obtain 24-hour urine specimen annually or more frequently depending on stone activity to assess adherence and metabolic response 4, 2
• Periodic blood testing is mandatory (Grade A evidence) to assess for adverse effects 4, 2:
  • Thiazides: hypokalemia and glucose intolerance 4, 2
  • Potassium citrate: hyperkalemia 4, 2, 5
  • Allopurinol and tiopronin: elevated liver enzymes 4
  • AHA and tiopronin: anemia and hematologic abnormalities 4

Obtain repeat stone analysis when available, especially in patients not responding to treatment, as stone composition may change (e.g., calcium oxalate to calcium phosphate) 4

Common Pitfalls to Avoid

• Do not restrict dietary calcium in calcium stone formers, as this increases oxalate absorption and stone risk 1, 2
• Do not use allopurinol as first-line therapy for uric acid stones; most patients need urinary alkalinization, not uric acid reduction 4, 5
• Do not use sodium citrate for alkalinization, as sodium increases urinary calcium excretion 1, 5
• Do not over-alkalize urine in calcium phosphate stone formers, as this decreases calcium phosphate solubility 1
• Do not forget to monitor for medication adverse effects with periodic blood testing 4, 2