What medications are used to treat calcium oxalate stones in the urine?

Medications for Calcium Oxalate Stones in Urine

Potassium citrate is the first-line medication for calcium oxalate stones in patients with low urinary citrate, while thiazide diuretics are indicated for those with hypercalciuria, and allopurinol is recommended for patients with hyperuricosuria. 1, 2

First-Line Medications Based on Metabolic Abnormalities

Potassium Citrate

• Indicated for patients with recurrent calcium stones who have low or relatively low urinary citrate excretion 1, 3
• Also beneficial for calcium stone-forming patients with normal citrate excretion but low urinary pH 1, 3
• Standard dosing:
  • Severe hypocitraturia (<150 mg/day): 60 mEq/day (30 mEq twice daily or 20 mEq three times daily) 4
  • Mild to moderate hypocitraturia (>150 mg/day): 30 mEq/day (15 mEq twice daily or 10 mEq three times daily) 4
• Potassium citrate is preferred over sodium citrate, as sodium load may increase urine calcium excretion 1
• Mechanism: Provides alkali load that increases urine pH and inhibits calcium phosphate crystallization 3, 5

Thiazide Diuretics

• Recommended for patients with high or relatively high urine calcium and recurrent calcium stones 1, 2
• Effective dosages include:
  • Hydrochlorothiazide: 25 mg twice daily or 50 mg once daily 1
  • Chlorthalidone: 25 mg once daily 1
  • Indapamide: 2.5 mg once daily 1
• Dietary sodium restriction should be continued when thiazides are prescribed to maximize the hypocalciuric effect 1
• Potassium supplementation may be needed when thiazide therapy is employed 1

Allopurinol

• Indicated for patients with recurrent calcium oxalate stones who have hyperuricosuria (>800 mg/day) and normal urinary calcium 1, 2
• Standard dosing: 200-300 mg/day for management of recurrent calcium oxalate stones in hyperuricosuric patients 6
• Dose may be adjusted based on 24-hour urinary urate determinations 6
• Hyperuricemia is not a required criterion for allopurinol therapy 1

Combination Therapy

• For patients with persistent stone formation despite addressing individual metabolic abnormalities, combination therapy may be necessary 1, 2
• Thiazides and potassium citrate can be used together for patients with both hypercalciuria and hypocitraturia 1, 7
• Adding potassium citrate to ongoing treatment programs (including thiazides and/or allopurinol) has been shown to reduce stone formation from 5.14 stones/patient-year to 1.33 stones/patient-year 5
• A recent study showed that potassium citrate was comparable to hydrochlorothiazide in reducing urinary calcium excretion while also significantly increasing citrate levels 7

Adjunctive Measures

• Increased fluid intake is essential regardless of medication choice (target urine volume of at least 2.5 L per day) 1, 2
• Sodium restriction enhances the effectiveness of both thiazide and potassium citrate therapy 1
• Dietary calcium should not be restricted as it may worsen stone formation 2
• For patients with enteric hyperoxaluria, higher calcium intake may be beneficial 1

Monitoring and Follow-up

• 24-hour urine specimen should be obtained within six months of initiating treatment to assess response to therapy 2
• Urinary citrate and/or pH should be measured every four months during potassium citrate therapy 1
• Monitor serum electrolytes, creatinine, and complete blood counts every four months during potassium citrate therapy 4
• Discontinue potassium citrate if hyperkalemia occurs 4

Common Pitfalls and Caveats

• Inadequate fluid intake remains a major risk factor for stone recurrence regardless of pharmacological intervention 2
• Potassium citrate doses greater than 100 mEq/day have not been studied and should be avoided 4
• Allopurinol should not be used as first-line therapy for uric acid stones, as most patients have low urinary pH rather than hyperuricosuria as the predominant risk factor 1
• Potassium citrate is contraindicated in patients with hyperkalemia or conditions predisposing to hyperkalemia 4