Thiazide does not affect urine oxalate excretion

Pharmacological interventions for preventing complications in idiopathic hypercalciuria

BACKGROUND

Idiopathic hypercalciuria is an inherited metabolic abnormality characterised by excessive amounts of calcium excreted into the urine in patients with normal serum levels of calcium. The morbidity of hypercalciuria is related to kidney stone disease and bone demineralization. In children, hypercalciuria can cause recurrent haematuria, frequency-dysuria syndrome, urinary tract infection and abdominal and lumbar pain. Several pharmacological treatments have been described that can decrease the levels of urinary calcium or its index of urinary crystallization.

OBJECTIVES

To assess the benefits and harms of pharmacological interventions for preventing complications and decreasing urological symptoms in patients with idiopathic hypercalciuria.

SEARCH STRATEGY

We searched MEDLINE, EMBASE, the Cochrane Renal Group's specialised register, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), handsearched relevant conference proceedings and reference lists of articles.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTS that compared any pharmacological intervention for preventing complications in idiopathic hypercalciuria, with placebo, other pharmacological intervention or a different administration mode or dose of the same treatment given for a minimum duration of four months and had a follow-up period of at least six months.

DATA COLLECTION AND ANALYSIS

Four authors assessed the studies for inclusion and extracted the data. Disagreements were resolved through discussion. Results were expressed as risk ratios (RR) with 95% confidence intervals (CI) or mean difference (MD).

MAIN RESULTS

Five studies (316 adult patients) were included. Four compared thiazides with standard treatment (periodic clinical follow-up and increased water intake) or specific dietary recommendations and one analysed the effect of thiazide plus a neutral potassium salt. There was a significant decrease in the number of new stone recurrences in those treated with thiazides (RR 1.61, 95% CI 1.33 to 1.96), although the follow-up periods varied. The stone formation rate also showed a statistically significant decrease in the patients treated with diuretics (MD -0.18, 95% CI -0.30 to -0.06). Thiazides plus potassium salts significantly decreased calciuria and vitamin D levels.

AUTHORS' CONCLUSIONS

There is some evidence that in patients with idiopathic hypercalciuria and recurrent stones, the addition of thiazides to a normal or modified diet for short to long periods (five months to three years) reduced the number of stone recurrences and decreased the stone formation rate. Thiazides and neutral potassium phosphate decreased calciuria in symptomatic patients with idiopathic hypercalciuria. There were no studies investigating the effect of pharmacological treatment on other clinical complications or asymptomatic idiopathic hypercalciuria.

Urine pH in renal calcium stone formers who do and do not increase stone phosphate content with time

BACKGROUND

Calcium phosphate (CaP) renal stones appear to be increasing in prevalence, and are caused by high urine CaP supersaturation, which arises from genetic hypercalciuria and high urine pH. Renal damage from stones or procedures, or treatments for stone could raise urine pH; alternatively pH may be intrinsically high in some people who are thereby predisposed to CaP stones.

METHODS

To distinguish these alternatives we sequenced changes in urine pH and stone CaP content asking which occurs first in patients whose stones showed progressive increase in CaP over time. From 4767 patients we found 62 in whom we could document transformation from calcium oxalate (CaOx) to CaP stones, and 134 CaOx controls who did not transform. Laboratory and clinical finding were contrasted between these groups.

RESULTS

Even when patients were forming relatively pure CaOx stones, those destined to increase stone CaP had higher urine pH than controls who never did so. Their higher pH was present before and during treatments to prevent new stone formation. Shock wave lithotripsy was strongly associated with increasing stone CaP but urine pH bore no relationship to number of procedures.

CONCLUSION

We conclude that high pH may not be acquired as a result of stones or their treatments but may precede transformation from CaOx to CaP stones and arise from diet or possibly heredity.

Extracorporeal renal lithotripsy: Evolution of residual lithiasis treated with thiazides

OBJECTIVES

To analyze the evolution of residual lithiasis after renal extracorporeal shock wave lithotripsy (ESWL) and to show the prolonged efficacy of thiazides in the treatment of residual lithiasis in patients with calcium lithiasis.

METHODS

We performed a longitudinal, analytical, 36-month study in 100 patients with residual calcium lithiasis after ESWL randomly distributed into two groups: 50 patients treated with placebo (controls, group 1) and 50 treated with hydrochlorothiazide, 50 mg/24 hr (group 2). All patients in both groups underwent imaging studies (simple radiography of the urinary tract and renal ultrasonography) and a metabolic urinary study.

RESULTS

The percentage of global expulsion of lithiasis during the follow-up period was significantly greater (chi-square exponent = 19.938, P = 0.001) in the patients treated with thiazides (72%) than in the control group (36%), although a large number of patients in this group underwent new ESWL sessions. During the follow-up period, we performed ESWL on 42% of the patients in group 1 and 18% of group 2, a statistically significant difference (chi-square exponent = 6.881, P = 0.032).

CONCLUSIONS

The results of our study have shown that residual lithiasis progresses in 58% of patients undergoing observation, and new ESWL sessions will be necessary in 42%. We observed a significant relationship between the presence of a urinary lithogenic pattern and the progression of the residual lithiasis. The administration of thiazides stabilizes or reduces the growth of residual lithiasis and favors its spontaneous elimination, thus reducing the need for new sessions of ESWL. This effect of thiazides is highly significant in patients presenting with hypercalciuria.

Thiazides Reduce Brushite, but not Calcium Oxalate, Supersaturation, and Stone Formation in Genetic Hypercalciuric Stone–Forming Rats

Over 59 generations, a strain of rats has been inbred to maximize urine calcium excretion. The rats now excrete eight to 10 times as much calcium as controls. These rats uniformly form calcium phosphate (apatite) kidney stones and have been termed genetic hypercalciuric stone-forming (GHS) rats. The addition of a common amino acid and oxalate precursor, hydroxyproline, to the diet of the GHS rats leads to formation of calcium oxalate (CaOx) kidney stones. Hydroxyproline-supplemented GHS rats were used to test the hypothesis that the thiazide diuretic chlorthalidone would decrease urine calcium excretion, supersaturation, and perhaps stone formation. All GHS rats received a fixed amount of a standard 1.2% calcium diet with 5% trans-4-hydroxy-l-proline (hydroxyproline) so that the rats would exclusively form CaOx stones. Half of the rats had chlorthalidone (Thz; 4 to 5 mg/kg per d) added to their diets. Urine was collected weekly, and at the conclusion of the study, the kidneys, ureters, and bladders were radiographed for the presence of stones. Compared with control, the addition of Thz led to a significant reduction of urine calcium and phosphorus excretion, whereas urine oxalate excretion increased. Supersaturation with respect to the calcium hydrogen phosphate fell, whereas supersaturation with respect to CaOx was unchanged. Rats that were fed Thz had fewer stones. As calcium phosphate seems to be the preferred initial solid phase in patients with CaOx kidney stones, the reduction in supersaturation with respect to the calcium phosphate solid phase may be the mechanism by which thiazides reduce CaOx stone formation.