Long-term follow-up of stone formers treated with a low dose of sodium potassium citrate

Phytate Effects on Incomplete Distal Renal Tubular Acidosis

Background: Adults who have incomplete distal renal tubular acidosis (dRTA) may present with recurrent urolithiasis due to metabolic acidosis, leading to bone resorption, which in turn causes hypercalciuria and urine alkalinization (pH > 6.0). Oral potassium citrate is the most commonly used treatment for dRTA, but some patients cannot tolerate this treatment. The objective of this single-arm study was to evaluate the effect of phytate, an inhibitor of bone resorption, on calciuria of patients with incomplete dRTA. Methods: The calciuria levels of 16 patients who had incomplete dRTA with urolithiasis and could not tolerate potassium citrate treatment were recorded before (baseline) and after 6 months of treatment with oral calcium magnesium phytate (380 mg every 12 h). There were no dietary modifications or other treatments. Results: The baseline calciuria was 317 ± 81 mg/24 h and the level after 6 months was 221 ± 38 mg/24 h (p < 0.005). Conclusions: Our results suggest that calcium magnesium phytate should be considered as an alternative or adjunctive treatment for hypercalciuria in patients with incomplete dRTA.

Primary Distal Renal Tubular Acidosis: Toward an Optimal Correction of Metabolic Acidosis

The term classic, type 1 renal tubular acidosis or primary distal renal tubular acidosis is used to designate patients with impaired ability to excrete acid normally in the urine as a result of tubular transport defects involving type A intercalated cells in the collecting duct. The clinical phenotype is largely characterized by the complications of chronic metabolic acidosis (MA): stunted growth, bone abnormalities, and nephrocalcinosis and nephrolithiasis that develop as the consequence of hypercalciuria and hypocitraturia. All these manifestations are preventable with early and sustained correction of MA with alkali therapy. The optimal target for plasma bicarbonate should be as close as possible to the range considered normal by current standards (between 23 and 28 mEq/L.). Most of the benefits of alkali therapy are tangible early in the course of the disease in childhood, but life-long treatment is required to prevent the vast array of complications attributable to chronic MA.

Is traditional stone clinic the optimal use of NHS resources?

There is no clear guidance on the efficacy of stone follow-up. NICE have been unable to make recommendations with current published evidence. The aim of this study was to understand the patient journey resulting in surgical intervention, and whether traditional stone follow-up is effective. A retrospective review of patients undergoing ureteroscopy (URS) or percutaneous nephrolithotomy (PCNL) over a 3 year period identified 471 patients who underwent these procedures to treat stone disease. Records were interrogated for the following: symptoms, mechanism of booking, reason for intervention, stone size, stone location, risk factors and previous follow-up. Of 471 patients who underwent intervention, 168 were booked from stone clinic follow-up (36%). Of these, 96% were symptomatic and 4% were asymptomatic. When risk factors were removed, this figure was reduced to 1%. Sepsis rate for emergency admissions differs between those followed up (13%) versus new presentations (19)%. There was no statistically significant difference in the outpatient imaging frequency between patients booked from an emergency admission (80% having imaging every 6 months) and those from the clinic (82%). Our Hospital provides on average 650 stone clinic appointments a year with a cost of £93,000. Given the low rate of intervention in patients with asymptomatic renal stones, a symptomatic, direct-access emergency stone clinic could be a better model of care and use of NHS resources. Urgent research is required in this area to further assess if this is the case.

Breaking the Cycle of Recurrent Calcium Stone Disease

Calcium stones are common and recurrent in nature, yet few therapeutic tools are available for secondary prevention. Personalized approaches for stone prevention have been informed by 24-hour urine testing to guide dietary and medical interventions. However, current evidence is conflicting about whether an approach guided by 24-hour urine testing is more effective than a generic one. The available medications for stone prevention, namely thiazide diuretics, alkali, and allopurinol, are not always prescribed consistently, dosed correctly, or tolerated well by patients. New treatments on the horizon hold the promise of preventing calcium oxalate stones by degrading oxalate in the gut, reprogramming the gut microbiome to reduce oxalate absorption, or knocking down expression of enzymes involved in hepatic oxalate production. New treatments are also needed to target Randall's plaque, the root cause of calcium stone formation.

Over-the-counter alkali agents to raise urine pH and citrate excretion: a prospective crossover study in healthy adults

OBJECTIVE

To assess the effect of two over-the-counter alkalizing agents on 24-hour urinary parameters.

MATERIALS AND METHODS

Ten healthy volunteers without a history of kidney stones were recruited to complete a baseline 24-hour urinalysis with a four-day diet inventory. Participants then maintained the same diet on either LithoLyte® (20 mEq two times per day) or KSPtabs^TM (1 tablet two times per day) and submitted another 24-hour urinalysis. The process was repeated with the other supplement. Urinary alkali parameters were compared to baseline, and side effects were elicited with a questionnaire.

RESULTS

LithoLyte® intake resulted in a non-significant increase in citrate (597 to 758 mg/day, p=0.058, an increase in urine pH (6.46 to 6.66, p=0.028), and a decrease in urine ammonium (41 to 36 mmol/day, p=0.005) compared to baseline. KSPtabs^TM resulted in an increase in citrate (597 to 797 mg/day, p=0.037) and urine pH (6.46 to 6.86, p=0.037), with a non-significant decrease in ammonium (41 to 34 mmol/day, p=0.059). No significant differences were seen comparing urinary analytes between LithoLyte® and KSPtabs^TM. With Litholyte®, no side effects, mild, moderate, and severe side effects were seen in 50%, 40%, 10%, and 0%, respectively. With KSPtabs^TM, rates were 60%, 20%, 10%, and 10%, respectively.

CONCLUSIONS

In healthy participants without a history of kidney stones, LithoLyte® and KSPtabs^TM are effective over-the-counter alkali supplements, with a similar side effect profile to prescription potassium citrate.

Risk factors for kidney stone disease recurrence: a comprehensive meta-analysis

Background

Kidney stone disease (KSD) is a common illness that causes an economic burden globally. It is easy for patients to relapse once they have suffered from this disease. The reported recurrence rate of KSD ranged from 6.1% to 66.9%. We performed this meta-analysis to identify various potential risk factors for the recurrence of KSD.

Methods

The PubMed, Embase and Web of Science databases were searched using suitable keywords from inception to Mar 2022. A total of 2,663 records were collected initially. After screening the literature according to the inclusion and exclusion criteria, 53 articles (40 retrospective studies; 13 prospective studies) including 488,130 patients were enrolled. The study protocol was registered with PROSPERO (No. CRD42020171771).

Results

The pooled results indicated that 12 risk factors including younger age (n = 18), higher BMI (n = 16), family history of kidney stones (n = 12), personal history of kidney stones (n = 11), hypertension (n = 5), uric acid stone (n = 4), race of Caucasian (n = 3), suspected kidney stone episode before the first confirmed stone episode (n = 3), surgery (n = 3), any concurrent asymptomatic (nonobstructing) stone (n = 2), pelvic or lower pole kidney stone (n = 2), and 24 h urine test completion (n = 2) were identified to be associated with KSD recurrence. In the subgroup analysis, patients with higher BMI (OR = 1.062), personal history of nephrolithiasis (OR = 1.402), or surgery (OR = 3.178) had a higher risk of radiographic KSD recurrence.

Conclusions

We identified 12 risk factors related to the recurrence of KSD. The results of this analysis could serve to construct recurrence prediction models. It could also supply a basis for preventing the recurrence of KSD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12894-022-01017-4.

HydroZitLa inhibits calcium oxalate stone formation in nephrolithic rats and promotes longevity in nematode Caenorhabditis elegans

Low fluid intake, low urinary citrate excretion, and high oxidative stress are main causative factors of calcium oxalate (CaOx) nephrolithiasis. HydroZitLa contains citrate and natural antioxidants and is developed to correct these three factors simultaneously. Antioxidants theoretically can prolong the lifespan of organisms. In this study, we preclinically investigated the antilithogenic, lifespan-extending and anti-aging effects of HydroZitLa in HK-2 cells, male Wistar rats, and Caenorhabditis elegans. HydroZitLa significantly inhibited CaOx crystal aggregation in vitro and reduced oxidative stress in HK-2 cells challenged with lithogenic factors. For experimental nephrolithiasis, rats were divided into four groups: ethylene glycol (EG), EG + HydroZitLa, EG + Uralyt-U, and untreated control. CaOx deposits in kidneys of EG + HydroZitLa and EG + Uralyt-U rats were significantly lower than those of EG rats. Intrarenal expression of 4-hydroxynonenal in EG + HydroZitLa rats was significantly lower than that of EG rats. The urinary oxalate levels of EG + HydroZitLa and EG + Uralyt-U rats were significantly lower than those of EG rats. The urinary citrate levels of EG + HydroZitLa and EG + Uralyt-U rats were restored to the level in normal control rats. In C. elegans, HydroZitLa supplementation significantly extended the median lifespan of nematodes up to 34% without altering feeding ability. Lipofuscin accumulation in HydroZitLa-supplemented nematodes was significantly lower than that of non-supplemented control. Additionally, HydroZitLa inhibited telomere shortening, p16 upregulation, and premature senescence in HK-2 cells exposed to lithogenic stressors. Conclusions, HydroZitLa inhibited oxidative stress and CaOx formation both in vitro and in vivo. HydroZitLa extended the lifespan and delayed the onset of aging in C. elegans and human kidney cells. This preclinical evidence suggests that HydroZitLa is beneficial for inhibiting CaOx stone formation, promoting longevity, and slowing down aging.

Metabolic assessment in pure struvite stones formers: is it necessary?

BACKGROUND AND OBJECTIVE

Magnesium ammonium phosphate stones (MAP), also known as struvite stones, are associated with urinary infection and impairment of renal unit. The aim of this study is to evaluate the urinary metabolic risk factors for recurrence of renal calculi in patients submitted to nephrectomy due to MAP stones.

METHODS

We retrospectively reviewed the charts of patients > 18 years old submitted to total nephrectomy due to pure MAP stones and pure calcium oxalate (CaOx) stones from July 2006 to July 2016. Urinary metabolic parameters were assessed through 24-hour urine exams ≥ 3 months after nephrectomy. Urinary metabolic parameters and new event related to lithiasis were compared.

RESULTS

Twenty-eight and 39 patients were included in MAP and CaOx group, respectively. Abnormalities in 24-hour urine samples were similar between groups. Hypercalciuria occurred in 7.1 and 10.3% of patients in MAP and CaOx group, respectively (p = 0.66), whereas hypocitraturia was present in 65.2 and 59.0% of patients with MAP and CaOx group, respectively (p = 0.41). No significant difference in new events was found between MAP and CaOx groups (17.9 vs. 23.1%, respectively; p = 0.60).

CONCLUSION

A 24-hour urine evaluation should be offered to patients submitted to nephrectomy due to pure MAP stones in order to detect metabolic risk, improve treatment, and prevent stone recurrence.

An Update on Evaluation and Management in Cystinuria

Cystinuria is the most common cause of inherited stone disease and is caused by the failure of absorption of filtered dibasic amino acids including cystine in the proximal tubules. It is associated with a very high recurrence rate in affected patients, with the potential for significant morbidity in such patients due to the need for repeated surgical interventions. A multimodal and multispecialty approach in a dedicated centre is the key to improving treatment outcomes and patient adherence to the treatment. This article reviews the latest knowledge on the clinical and diagnostic features and summarises key developments to aid clinicians in diagnosis and management options, together with future directions for the care of these patients.

Innovative prolonged-release oral alkalising formulation allowing sustained urine pH increase with twice daily administration: randomised trial in healthy adults

A multi-particulate fixed-dose combination product, consisting of a combination of two alkalising salts formulated as prolonged-release granules, ADV7103, was developed to obtain a sustained and prolonged alkalising effect. The specific release of both types of granules was shown in vitro through their dissolution profiles, which indicated that potassium citrate was released within the first 2-3 h and potassium bicarbonate up to 10-12 h after administration. The long-lasting coverage of ADV7103 was confirmed through a randomised, placebo-controlled, double-blind, two-period study, measuring its effect on urine pH in healthy adults (n = 16) at doses of alkalising agent ranging between 0.98 and 2.88 meq/kg/day. A significant increase of urine pH with a positive dose-response in healthy adult subjects was shown. Urine pH above 7 was maintained during 24 h with a dosing equivalent to 1.44 meq/kg twice a day, while urine pH was below 6 most of the time with placebo. The effect observed was non-saturating within the range of doses evaluated and the formulation presented a good safety profile. ADV7103 provided an effective prolonged release of alkalising salts to cover a 12-h effect with adequate tolerability and could afford a twice a day (morning and evening) dosing in patients requiring long-term treatment.

Using Low-Calorie Orange Juice as a Dietary Alternative to Alkali Therapy

Purpose: The pursuit of a dietary source to increase urine pH and citrate in stone formers has been ongoing for >30 years. Early evidence showed that orange juice (OJ) contains alkali and citrate, but high sugar and ascorbic acid content limited the use of OJ as a viable daily source of alkali. Recently, novel low-calorie OJs have emerged and could potentially be a better option. Methods: Beverages with high concentrations of alkali citrate and malate were identified using ion chromatography. Two low-calorie OJ beverages, in addition to crystal light lemonade beverage (CLLB), were chosen. Healthy volunteers (5 men, 5 women) drank 1 L of OJ or CLLB with 1 L water daily for 7 days, and then completed a 24-hour urinalysis. A washout week was instituted between trial weeks. The study design is a prospective randomized crossover control trial. A paired analysis using comparison of means was used to evaluate low-calorie OJ and CLLB. Volunteers had no prior history of kidney stones and maintained a journal with beverage compliance, side effect (SE), and dietary consumption data. Results: Tropicana 50 (TRP50), Kroger low-calorie OJ (KLCO), and CLLB were found to have a total alkali content of 56.60, 47.9, and 17.3 mEq/L, respectively, based on ion chromatography. Consumption of all three beverages raised urinary citrate (116.6 [-118 to 373, 177.9 [-3 to 359], 155.6 [-4 to 237] ▵mg/day 95% confidence interval) and urinary pH (0.25 [0.08-0.53], 0.74 [0.41-1.07 p < 0.05], 0.25 [0.25-0.64]), respectively, compared with water phase. Based on journal entries by volunteers, TRP50 had the most SEs (90% participants) felt to be a result of the artificial sweetener (Stevia^®). Conclusion: Low-calorie OJs, and to a lesser extent CLLB, have alkali and citrate based on ion chromatography. Daily consumption by healthy volunteers of KLCO can raise urinary pH.

Investigational Therapies for Primary Hyperoxaluria

Recent years have brought exciting new insights in the field of primary hyperoxaluria (PH), both on a basic research level as well as through the progress of novel therapeutics in clinical development. To date, very few supportive measures are available for patients suffering from PH, which, together with the severity of the disorder, make disease management challenging. Basic and clinical research and development efforts range from correcting the underlying gene mutations, preventing calcium oxalate crystal-induced kidney damage, to the administration of probiotics favoring the intestinal secretion of excess oxalate. In this review, current advances in the development of those strategies are presented and discussed.

Coconut Water: An Unexpected Source of Urinary Citrate

Purpose

Coconut water has long been touted for its medicinal qualities including natural hydration. We sought to determine whether its consumption would induce changes to urinary lithogenic factors beyond changes in urine volume.

Materials and Methods

After Institutional Review Board approval, volunteers with no prior history of nephrolithiasis were recruited. Each participant was randomized initially to either the coconut water or the water phase of the study. Participants kept meticulous food and fluid intake logs during the first phase of the study and were asked to replicate that diet for the second phase. For each phase the participant consumed 2L of either Taste of Nirvana® pure coconut water or tap water daily for four days. Participants were not restricted to consume additional fluid of their choice during their assigned study phase. During days 3 and 4 of each phase the participant collected a 24-hour urine specimen. Coconut water citrate and malate content were measured and were used along with the beverage pH to calculate the total alkali content of the coconut water. Supersaturation levels were calculated using Equil2. Nonparametric paired analysis using the Wilcoxon test was performed for statistical analysis.

Results

There were 4 adult male and 4 adult female participants. Each individual's 24-hour urine collection had a creatinine excretion within 20% of the mean for each subject's four samples corroborating that all samples were collected properly. The two samples from each phase for each individual were averaged. The coconut water itself was also analyzed and it was calculated to have a total alkali content of 13.8 mEq/L. Consumption of coconut water significantly increased urinary citrate (29%, p=0.02), urinary potassium (130%, p=0.01), and urinary chloride (37%, p=0.03), without affecting urine pH (p=0.16) or volume beyond that of tap water (p=1.00).

Conclusions

Coconut water consumption increases urinary potassium, chloride, and citrate in nonstone forming individuals.

Do "inhibitors of crystallisation" play any role in the prevention of kidney stones? A critique

A critical examination of data in the literature and in as yet unpublished laboratory records on the possible role of so-called inhibitors of crystallisation in preventing the formation of calcium-containing kidney stones leads to the following conclusions. So-called inhibitors of spontaneous "self-nucleation" are unlikely to play any role in the initiation of the crystallisation of CaOx or CaP in urine because excessive urinary supersaturation of urine with respect to these salts dominates the onset of "self-nucleation" within the normal time frame of the transit of tubular fluid through the nephron (3-4 min). Inhibitors of the crystal growth of CaOx crystals may or may not play a significant role in the prevention of CaOx stone-formation since once again excessive supersaturation of urine can overwhelm any potential effect of the inhibitors on the growth process. However, they may play a role as inhibitors of crystal growth at lower levels of metastable supersaturation when the balance between supersaturation and inhibitors is more equal. Inhibitors of CaOx crystal aggregation may play a significant role in the prevention of stones, since they do not appear to be strongly affected by excessive supersaturation, either in vitro or in vivo. Inhibitors of CaOx crystal binding to renal tubular epithelium may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones in the renal tubules. Inhibitors of CaOx crystal binding to Randall's Plaques and Randall's Plugs may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones on renal papillae. There may be an alternative explanation other than a deficiency in the excretion of inhibitors for the observations that there is a difference between CaOx crystal size and degree of aggregation in the fresh, warm urines of normal subjects compared those in urine from patients with recurrent CaOx stones. This difference may depend more on the site of "self-nucleation" of CaOx crystals in the renal tubule rather than on a deficiency in the excretion of so-called inhibitors of crystallisation by patients with CaOx stones. The claim that administration of potassium citrate, potassium magnesium citrate or magnesium hydroxide reduces the rate of stone recurrence may be due to the effect of these forms of medication on the supersaturation of urine with respect to CaOx and CaP rather than to any increase in "inhibitory activity" attributed to these forms of treatment. In summary, there is a competition between supersaturation and so-called inhibitors of crystallisation which ultimately determines the pattern of crystalluria in stone-formers and normals. If the supersaturation of urine with respect to CaOx reaches or exceeds the 3-4 min formation product of that salt, then it dominates the crystallisation process both in terms of "self-nucleation" and crystal growth but appears to have little or no effect on the degree of aggregation of the crystals produced. At supersaturation levels of urine with respect to CaOx well below the 3-4 min formation product of that salt, the influence of inhibitors increases and some may affect not only the degree of aggregation but also the crystal growth of any pre-formed crystals of CaOx at these lower levels of metastability.

Dietary recommendations and treatment of patients with recurrent idiopathic calcium stone disease

This review describes the various dietary regimens that have been used to advise patients on how to prevent the recurrence of their calcium-containing kidney stones. The conclusion is that although there is some general advice that may be useful to many patients, it is more efficacious to screen each patient individually to identify his/her main urinary, metabolic, nutritional, environmental, and lifestyle risk factors for stone-formation and then tailor specific advice for that particular patient based on the findings from these investigations. If the patient can be motivated to adhere strictly to this conservative approach to the prophylactic management of their stone problem over a long time period, then it is possible to prevent them from forming further stones. This approach to stone management is considerably less expensive than any of the procedures currently available for stone removal or disintegration. In the UK, for each new stone episode prevented by this conservative approach to prophylaxis it is calculated to save the Health Authority concerned around £2000 for every patient treated successfully. In the long term, this accumulates to a major saving within each hospital budget if most stone patients can be prevented from forming further stones and when the savings are totalled up country-wide saves the National Exchequer considerable sums in unclaimed Sick Pay and industry a significant number of manpower days which would otherwise be lost from work. It is also of immense relief and benefit to the patients not to have to suffer the discomfort and inconvenience of further stone episodes.

Should we modify the principles of risk evaluation and recurrence preventive treatment of patients with calcium oxalate stone disease in view of the etiologic importance of calcium phosphate?

Prevention of recurrent calcium oxalate (CaOx) stone formation in the urinary tract is important to avoid negative effects on renal function, patient suffering and to reduce health care cost. Present shortcomings in this regard can be explained both by insufficient understanding of the mechanisms of stone formation and by poor patient compliance to those regimens that nevertheless have proven effective. During the past years, we have got increased insights in the nature of CaOx stone formation and it is suggested that the improved understanding of this process can be used for a more dynamic risk evaluation and treatment regimen directed to specific risk periods that can be identified in the individual patients. Some of the possibilities with regard to the important role of calcium phosphate are discussed in this article.

[Evidence-based pharmacological metaphylaxis of stone disease]

Approximately one-fourth of urolithiasis patients are at high risk for recurrent stone formation or severe metabolic disturbances. These patients need specific metaphylaxis for effective stone prevention, adjusted to their individual metabolic risk. Recent recommendations for the pharmacological treatment of stone diseases are summarized in this article. For the different treatment options, evidence from the literature was assessed. In addition, a follow-up concept for pharmacologically treated high-risk stone formers is discussed.

Patients’ attitudes on how to deal with the risk of future stone recurrences

One hundred consecutive patients referred for active stone removal responded to a number of questions regarding their attitude to metabolic risk evaluation and recurrence prevention. Of the 74 men and 26 women all but one were interested in the cause of their disease. While 95% of the patients were motivated to change their dietary habits, only 71% were interested in pharmacological treatment. Collection of 24-h urine for risk evaluation in one or five fractions was acceptable to 94 and 84% of the patients, respectively. Only 79% wanted to collect urine during more than one 24-h period. Given the option of a recurrence prevention programme or active stone removal when or if a stone appeared, approximately half of our patients (52%) chose the first, and about one-third (29%) of them chose the second alternative, whereas as many as 19% of the patients did not express any opinion. A programme for regular follow-up in order to detect new stones early was appreciated by only 81 patients. These results show that biochemical risk evaluation and recurrence prevention is generally met with a positive attitude by most patients and that medical recurrence prevention appears to be appreciated by more than half of the patients.

Diagnosis and metaphylaxis of stone disease. Consensus concept of the National Working Committee on Stone Disease for the upcoming German Urolithiasis Guideline

This review draws the recent state of the art in metabolic diagnosis and metaphylaxis of stone disease. It is the basis for the consensus approval with the other medical societies and institutions in Germany involved in the guideline process of the new "Urolithiasis Guideline". The German Working Committee on Stone Disease reviewed critically the current literature in the field of urolithiasis-including the existing German and EAU-Guidelines as well as the Conference Book of the First International Consultation on Stone Disease. As far as possible the references were rated according to the EBM criteria. On this basis the expert group discussed all pathways and statements regarding the management of stone disease. The present review coincides with the consented guideline draft of the German Working Committee on Stone Disease. Occurrence of stone disease in the western world increases seriously. Modern lifestyle, dietary habits and overweight-problems of the affluent societies-emerge to be the important promoters of the "stone-boom" in the new millennium. This even affects children, whose stone prevalence is otherwise significantly less than that of adults. Criteria for the high risk group of stone formers were clearly defined. A diagnostic standard is formulated for the basic and the elaborate metabolic evaluation of a stone patient. Approximately 75% of all stone patients could anticipate stone recurrence with elementary reorientation of their lifestyle and dietary habits, summarized as general metaphylaxis. About 25% of the stone formers require additional pharmacological intervention to normalize their individual biochemical risk, precisely compiled for each stone type as specific metaphylaxis.

[Prevention of nephrolithiasis. Established strategies and new concepts]

During the last 2 decades in Germany, only minor efforts were expended for the prevention of urinary stones. Substantial technical progress simplified the treatment of existing calculi; thus, it was more convenient to treat a new stone than to prevent its recurrence. But times change! In these days of financial squeeze in the medical system, prevention becomes more attractive. Nevertheless, strategies for kidney stone prevention developed. Established concepts for dietary advice were rejected due to the results of new randomized studies. Moreover, new pharmacological substances were introduced for metaphyalxis. The new concepts are feasible for the daily routine. For some treatment modalities in stone prevention, there is valid evidence from the literature, which should encourage us to adopt these modalities in the future. A number of drugs are used as "good common practice" without any proof from a randomized trial. Often prospective and valid studies are not available. The present paper intends to describe the status quo of nephrolithiasis prevention in Germany, focussing on confirmed data and unsolved problems.

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.

Metabolic evaluation and therapy

The recurrent formation of stones in the urinary tract is a well-recognized clinical problem. Unfortunately, progress in the medical care of these patients has not paralleled that of the surgical care. There are, however, several steps that can be taken to reduce the recurrence rate. In this regard it is desirable to identify patients at risk and to find risk factors that need to be eliminated. The extent of biochemical evaluation and the form of stone preventive treatment in patients with calcium stone formation is presently a matter of debate. This review focuses on some current aspects on the analysis of risk factors for calcium stone formation. The present situation on recurrence prevention using dietary and pharmacological measures is also summarized.