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Common Urological Problems

Urinary Stone Disease Prevention

  • - General Urology - Common Urological Problems - Urinary Stone Disease
  • Jul 25, 2010
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  • Viewed: 13158
Tags: | absorptive hypercalciurics | alkalinizing ph agents | calcium nephrolithiasis | computed tomography |

In general,  50%  of patients experience recurrent urinary stones within 5 years without prophylactic intervention.

Appropriate education and preventive measures are best instituted with a motivated patient after spontaneous stone passage or surgical stone removal. Risk factors as described previously should be identified and modified, if possible.

Irrespective of the final metabolic evaluation and stone analysis, the patient’s fluid intake should be about 1.6 L/ 24 h. Fluids should be encouraged during mealtime. Additionally, liquids should be increased approximately 2 hours after meals.  Water produced as a metabolic by-product reaches its nadir at this time, and thus the body is relatively dehydrated. Fluid ingestion also should be encouraged to force a nighttime diuresis adequate to awaken the patient to void. Awakening and ambulating to void limit urinary stasis and offer an opportunity to ingest additional fluids.

These lifestyle changes are difficult to maintain and should be encouraged during subsequent office visits. Motivated patients who regularly return to a urinary stone clinic have a reduced stone recurrence rate that is probably due to increased compliance.

A systematic metabolic evaluation should be instituted after a patient has recovered from urinary stone intervention or spontaneous stone passage.  Stone analysis should be obtained to help direct the workup. An outpatient urine collection during typical activities and fluid intake helps unmask significant abnormalities. An initial 24-hour urine collection for calcium stone formers should include tests for calcium,  uric acid,  oxalate,  citrate,  sodium,  volume, and pH.  An open dialog with local laboratories helps to standardize collection routines and determine whether an outside laboratory is preferred.  Baseline serum levels for blood urea nitrogen,  creatinine,  calcium,  phosphorous, and uric acid are appropriate.

Urinary Stone Disease

Urinary Stone Disease

Hypercalciuria is the most common abnormality.  To differentiate among hypercalciuria types I,  II,  and III,  a patient should be placed on a sodium-  and calcium-restricted diet for a few days to a week.  This is easily achieved (100 mEq/day)  by eliminating table salt and reducing obviously salty foods. Calcium is restricted (400–500 mg)  by excluding dairy products.  A repeat 24-hour urine collection is evaluated for calcium. A urinary calcium level <250 mg/day confirms a diagnosis of dietary-dependent hypercalciuria type II. Type I and type III hypercalciuria must be differentiated in patients with urinary calcium levels >250 mg/day.  A calcium binder such as cellulose phosphate is prescribed (5 g three times daily with meals) for a few days. This is followed by a repeat 24-hour urine calcium level and parathyroid hormone blood value. Patients who have type I absorptive hypercalciuria have at least a 50% drop in urinary calcium levels and normal parathyroid hormone levels.

Hyperuricosuria, hyperoxaluria, and hypocitraturia calcium stone formers can be treated appropriately and followed with repeat 24-hour urine collections.  Many calcium stone formers have multiple defects;  although one treatment may reverse one defect, it may exacerbate others.

Subsequent 24-hour urine collections are critical for effective long-term follow-up and stone prevention. Treatment of cystinuria should be titrated with repeat 24-hour cystine levels. Repeat urine cultures should be obtained in patients with infectious calculi.

1. Alkalinizing pH agents-
Potassium citrate is an oral agent that elevates urinary pH effectively by 0.7–0.8 pH units.  Typical dosing is 60 mEq in 3 or 4 divided doses daily. It is available in wax-matrix 10-mEq tablets, liquid preparations, and crystals that must be mixed with fluids.  The effect is maintained over many years. 

Care should be taken in patients susceptible to hyperkalemia, those with renal failure, and those taking potassium-sparing diuretics. Although the medication is usually well tolerated, some patients may complain of abdominal discomfort, especially with tablet preparations. It is indicated in those with calcium oxalate calculi secondary to hypocitraturia (<320 mg/day),  including those with renal tubular acidosis. Potassium citrate also may be used effectively to treat uric acid lithiasis and nonsevere forms of hyperuricosuric calcium nephrolithiasis.

Sodium and potassium bicarbonate, orange juice, and lemonade are alternative alkalinizing agents. There are no effective long-term urinary acidifying agents.

2. Gastrointestinal absorption inhibitor-
Cellulose phosphate binds calcium in the gut and thereby inhibits calcium absorption and urinary excretion. It is a popular drug in the treatment of absorptive hypercalciuria type I with recurrent calcium nephrolithiasis, although it only prevents new stone formation. Patients should have normal parathyroid hormone values, normal serum calcium and phosphate values, no evidence of bone disease, and evidence of increased intestinal calcium absorption. The drug decreases the urinary saturation of calcium phosphate and calcium oxalate.

It may increase urinary oxalate and urinary phosphate levels. A typical starting dosage is 5 g three times daily with meals; the dosage may be titrated by following 24-hour urinary calcium levels. Urinary magnesium, calcium, oxalate, and sodium levels and serum parathyroid hormone should be monitored one to two times yearly. Magnesium supplements are frequently required and should be taken at least 1 hour before or after cellulose phosphate is taken. Cellulose phosphate is associated with a sodium load and should be used with caution in those with congestive heart failure. Gastrointestinal side effects are infrequent; they include dyspepsia and loose bowel movements.

Cellulose phosphate may be suboptimal treatment for postmenopausal women who are at risk for bone disease.

An alternative treatment for such patients would be hydrochlorothiazides supplemented with potassium citrate to offset the potential hypokalemia and hypocitraturia.

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