Clinical results of allopurinol treatment in prevention of calcium oxalate stone formation

Metabolic risk-evaluation and prevention of recurrence in stone disease: does it make sense?

In this review, aspects on the importance of information on urine composition and selection of the most appropriate regimen for prevention of recurrence are discussed. For patients with urolithiasis the treatment is facilitated by urine analysis with estimates of supersaturation levels. Despite lack of strong scientific evidence for the benefit of selective versus non-selective prevention of recurrence in patients with calcium stone disease, there is currently both convincing and logical information in support of tailored/selective treatment regimens aiming at correction of abnormal target variables. Such an approach is also recommended in the EAU and AUA guidelines. It is important, however, that every preventive regimen is balanced between the effects on urine composition and patients' tolerance to the treatment in order to achieve satisfactory compliance. It is possible that future improved understanding of the causes of calcium stone formation might provide a different therapeutic approach.

Idiopathic calcium oxalate urolithiasis: risk factors and conservative treatment

Idiopathic calcium oxalate urolithiasis is a frequent and recurrent multifactorial disease. This review focuses on urinary and dietary risk factors for this disease and conservative strategies for rectifying them. Dietary oxalate and calcium and their respective urinary excretions have been extensively investigated during the last 10 years. Urinary oxalate has emerged as the most important determinant of calcium oxalate crystallization while the role of urinary calcium has shifted to bone balance and osteoporosis. Dietary calcium restriction increases urinary oxalate and contributes to a negative bone balance. It has therefore been abandoned as a means to reduce the risk of calcium oxalate kidney stone formation. Calcium oxalate kidney stone patients are advised to increase their fluid intake to achieve a urine volume of 2 l or more; the recommended calcium intake is 800-1200 mg/day; high oxalate foods should be restricted; daily protein intake should be between 0.8 and 1 g/kg body weight/day; essential fats should be included; vegetable and fruit (except oxalate-rich vegetables) intake should be increased. The use of calcium supplements has potential benefits but needs to be examined further.

Epidemiology and medical management of stone disease

Recurrent stone formation in the urinary tract is a common and important problem that must be considered in daily urological practice. With a prevalence of> 10% and an expected recurrence rate of approximately 50%, stone disease has an important effect on the healthcare system. It is generally agreed that patients with uric acid/urate, cystine or infection stones always should be treated pharmacologically. For calcium stone formers the treatment should be chosen according to the severity of the disease. Recurrence in patients with calcium-stone disease can be prevented with general or specific dietary and drinking advice, and with pharmacological therapy. For idiopathic calcium stone formers the most convincing therapeutic effects have been reported with thiazide and alkaline citrate.

Development of metaphylaxis in calcium urolithiasis: a restriction of conventional drug therapy

Between 1978 and 1992 (mean 9.2 years), metaphylaxis was introduced to 110 patients originally hospitalized for recurrent urinary calcium stones (mostly bilateral or multiple). Patients with hyperparathyroidism or with sponge kidney were excluded from the study. Until 1984, the condition had been treated mostly using conventional drug metaphylaxis (thiazides and allopurinol in 75% and 57%, respectively). After that year, there was a gradual decrease in the number of patients treated with thiazides (to 15%) and allopurinol (to 10%). This was associated with a steep rise in the proportion of patients treated with inhibitors (magnesium to 36% and citrates to 30%), or exclusively with non-medicamentous therapy (to 31%). These fundamental changes in approach have not reduced the effectiveness of metaphylaxis, and recurrence rates in individual years have not changed significantly either. Metaphylaxis was successful in 105 patients (95%) and the rate of recurrence has declined from 0.9 to 0.08 stones per year. The restriction of conventional drug metaphylaxis has entailed a marked decrease in the incidence of side effects of therapy and, consequently, a reduced need for follow-up tests and outpatient follow-up.

Allopurinol and thiazide effects on new urinary stone formed after discontinued therapy in patients with urinary stones

We treated 87 patients with calcium-containing urinary stones with either allopurinol alone (44 patients) or in combination with thiazide (43 patients) and studied new stone formation before, during, and after the discontinuation of the drug therapy. The number of stones formed were 1.18, 0.24, and 0.13 before, during, and after discontinuation of the drug therapy, respectively, in the patients treated with allopurinol alone and 1.32, 0.20, and 0.09 in those treated in combination with thiazide. No differences were observed in these values and the duration of each observation period between the two groups. Decreases in the incidence of stone formation even after interruption of drug therapy suggested that recurrence-preventive effects observed following administration of these drugs include the effects of medical guidance. However, allopurinol therapy was effective in preventing recurrence in patients with hyperuricosuria.

Does hyperuricosuria play a role in calcium oxalate lithiasis?

This review evaluates the epidemiologic, clinical and experimental evidence for an etiological link between urinary uric acid and the propensity to develop calcium oxalate calculi. While epidemiologic and laboratory studies provide only equivocal support for a synergistic relationship, several clinical trials with allopurinol have demonstrated a reduction in calculus recurrence. These beneficial effects are observed only when allopurinol is given to subjects with calcium oxalate calculi who have isolated hyperuricosuria. The specificity of this effect suggests that there is an important interaction between uric acid and calcium oxalate but the mechanism(s) remain to be elucidated.