How to prevent urinary stone formation

The age of the patient and the severity of the problem affect both the need for and the kind of prophylaxis.

Idiopathic stone-formers

Where no metabolic abnormality is detected, the basis of prevention is continuation of a high intake of fluid all through the day and night. The aim should be to make sure a daily urine volume of 2-2.5 L, which requires a fluid intake in surplus of this, considerably so in the case of those who live in hot countries or work in a hot surroundings.

Idiopathic hypercalciuria

Severe dietary calcium restriction is unsuitable. Patients should be encouraged to eat a normal-calcium (30 mmol/day) diet. Dietary calcium limit results in hyper absorption of oxalate, and so foods containing excessive amounts of oxalate should also be restricted. A high fluid drinking is recommended as for idiopathic stone-formers. Patients who reside in a hard water region may benefit from intake of softened water. If hypercalciuria persists and stone formation continues, a thiazide diuretic is used (e.g. bendroflumethiazide 2.5 or 5 mg every morning). Thiazides decrease urinary calcium excretion by a direct action on the renal tubule. Thiazides may precipitate diabetes mellitus or gout and worsen their hyper cholesterolaemia. Decrease the intake of animal proteins to 50 g/day and sodium intake to 50 mmol/day is also advisable, as a randomized controlled trial has found that a diet restricted in animal protein and salt but with normal calcium was more effective in the prevention of calcium and particularly oxalate stones than a diet restricted in calcium.


Mixed infective stones

Recurrent stones of these kinds should be prevented by continuance of a high fluid drinking and scrupulous control of bacteriuria. This will need long-term follow-up and frequently the use of long-term low-dose prophylactic antibacterial drugs.

Uric acid stones

Dietary measures are probably of negligible value and are hard to put into practice. Successful prevention can be achieved by the long-term use of allopurinol to preserve the serum urate and urinary uric acid excretion in the physilogical range. A high fluid drinking should also be continued. Uric acid is more soluble at alkaline pH, and long term sodium bicarbonate supplementation to preserve an
alkaline urine is an substitute approach in those few patients, who are not capable to take allopurinol. However, alkalinization of the urine favors precipitation of
calcium oxalate and phosphate.

Cystine stones

These can be prevented and indeed will dissolve slowly with a high fluid intake. Five litres of water has to be drunk each 24 hours, and the patient must wake twice in the night to drink 500 ml or more of water. Many patients cannot accept this regimen. An alternative, though in fact more bothersome, option is the long-term intake of the chelating agent penicillamine; this helps cystine to be transformed to the more soluble penicillamine-cysteine complex. Side-effects of penicillamine are drug rashes, blood dyscrasias and immune complex-mediated glomerulonephritis. However, it is especially effective fo the dissolution of the existing cystine stones.

Mild hyperoxaluria with calcium oxalate stones

A high fluid ingestion and dietary oxalate constraint are necessary. Dietary advice as in hypercalciuria is to be followed.

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