Maintenance Therapy for Kidney Stones
For patients with a history of kidney stones, maintenance therapy should include increased fluid intake to achieve at least 2 liters of urine per day, with additional pharmacologic therapy (thiazide diuretics, potassium citrate, or allopurinol) based on stone type and metabolic abnormalities. 1
General Recommendations for All Stone Types
Fluid Intake
- Increase fluid intake to achieve at least 2-2.5 liters of urine output per day 1, 2
- For cystine stone formers, higher fluid intake of at least 4 liters per day is required to reduce urinary cystine concentration below 250 mg/L 3, 1
- Beverages like coffee, tea, wine, and orange juice may be associated with lower risk of stone formation, while sugar-sweetened beverages should be avoided 2
Dietary Modifications
- Maintain normal dietary calcium intake (1,000-1,200 mg/day) rather than restricting calcium 2, 4
- Limit sodium intake to 2,300 mg daily or less 1, 2, 4
- For calcium oxalate stones, limit intake of oxalate-rich foods while maintaining normal calcium consumption 2, 4
- Avoid calcium supplements, which may increase stone risk unlike dietary calcium 2
- For cystine stones, limit both sodium and animal protein intake 1, 3
Pharmacologic Therapy Based on Stone Type
Calcium Stones with Hypercalciuria
- Thiazide diuretics are the standard therapy for calcium stone formers with idiopathic hypercalciuria 1, 5
- Effective thiazide dosages include hydrochlorothiazide (25 mg twice daily or 50 mg once daily), chlorthalidone (25 mg once daily), or indapamide (2.5 mg once daily) 1
- Potassium supplementation may be needed with thiazide therapy to prevent hypokalemia 1
Calcium Stones with Hypocitraturia
- Potassium citrate therapy is recommended for patients with low or relatively low urinary citrate 1, 6
- Potassium citrate is preferred over sodium citrate, as sodium load may increase urine calcium excretion 1, 5
- Dosage typically ranges from 30 to 100 mEq per day, usually administered as 20 mEq three times daily 6
- Potassium citrate therapy has been shown to increase urinary citrate excretion from subnormal to normal values and increase urinary pH from 5.6-6.0 to approximately 6.5 6
Calcium Oxalate Stones with Hyperuricosuria
- Allopurinol is recommended for patients with recurrent calcium oxalate stones who have hyperuricosuria and normal urinary calcium 1, 5
- Hyperuricemia is not a required criterion for allopurinol therapy 1
Uric Acid Stones
- Alkalinization of urine to pH 6.0-7.0 with potassium citrate is first-line therapy 7, 5
- Potassium citrate therapy has been shown to effectively reduce stone formation in patients with uric acid lithiasis 6
Cystine Stones
- High fluid intake (at least 4 liters per day) is particularly important 3, 1
- Limit sodium and protein intake 1, 3
- Urinary alkalinization with potassium citrate to increase pH to approximately 7.0 3, 7
- For unresponsive cases, cystine-binding thiol drugs like tiopronin may be considered 3, 5
Monitoring and Follow-up
- Obtain a 24-hour urine specimen within six months of initiating treatment to assess response 2, 3
- Annual 24-hour urine specimens are recommended for long-term follow-up 2, 7
- Stone analysis should be obtained at least once when stone material is available to guide prevention strategies 2
Effectiveness of Maintenance Therapy
- Potassium citrate therapy has been shown to reduce stone formation rates significantly across different patient groups 6
- In patients with hypocitraturic calcium oxalate nephrolithiasis, potassium citrate therapy achieved remission (defined as freedom from newly formed stones) in 80% of patients 6
- Thiazide therapy effectively reduces recurrence in calcium stone formers with hypercalciuria 1, 5
- Allopurinol reduces the risk of recurrent calcium oxalate stones in patients with hyperuricosuria 1
Remember that maintenance therapy should be tailored based on stone composition and underlying metabolic abnormalities, with the primary goal of reducing urinary supersaturation of stone-forming salts.