The effects of sodium citrate and oral potassium citrate on urease-induced crystallization

[Nephrolithiasis: metabolic defects and terapeutic implications]

Over the past 10 years, major progress has been made in the knowledge of urinary lithogenesis, including the potential pathogenetic role of Randall's plaques and renal tubular crystal retention. Urine supersaturation is the driving force of this process and can be induced by some risk factors, including low urine volume, high urinary excretion of calcium oxalate and uric acid and low urinary excretion of citrate. Primary hypercalciuria can be due to intestinal overabsorption renal leak and bone reabsorption of calcium. Prophilaxis is mainly conducted with thiazides and low calcium diet which is indicated only in the intestinal form. Primary hyperoxaluria is treated with pyridoxine and may require in the severe forms simultaneous renal and liver transplantation. Enteric hyperoxaluria is secondary to fatty acids malabsorption and requires diet, oral calcium and cholestiramine. Hyperuricosuria is caused by diet endogenous overproduction, mainly due to enzymatic defects or high renal excretion of uric acid. Urine alkalinization with K or K and Mg citrate can prevent stone formation even in idiopathic uric acid nephrolithiasis, in which a defect of urine acidification is supposed to be the main abnormality, and in hypocitraturic patients. Cystinuria is a rare inherited defect with an intense clinical impact. It can be classified in three forms and urinary stone formation is the role. Increased solubility and conversion of cystine in a more soluble form are the main goals of the prophylaxis which includes K citrate and thiol agents administration. Tiopronin is preferred to D-penicillamine due to its lower side effects.

Strategy to control catheter encrustation with citrated drinks: a randomized crossover study

PURPOSE

Nucleation pH is the pH at which Ca and Mg come out of urine to form crystals. If the safety margin between voiding pH and nucleation pH could be increased, it would increase the possibility of an alternative to controlling the activity of urease producing bacteria as a strategy to control catheter encrustation.

MATERIALS AND METHODS

We performed a 6-week randomized crossover study in 24 patients with catheter blockage who were randomly allocated to a specific sequence of 3 consecutive available treatments, including increased fluid intake, lemon juice and potassium citrate. Each patient received all available regimens. At the end of each week 24-hour urine samples were analyzed for voiding and nucleation pH, citrate, Ca and Mg.

RESULTS

Mean +/- SD nucleation pH increased from 7.45 +/- 0.60 at baseline to 7.93 +/- 0.50, 7.68 +/- 0.64 and 7.96 +/- 0.37 in the lemon juice, increased fluid intake and potassium citrate groups, respectively (p <0.0001). Mean urinary citrate increased significantly (p <0.0001), in particular due to lemon juice and potassium citrate effects. The association between treatment and Ca was weak (p = 0.12) while that of Mg was negative due to lemon (p <0.001). Average increase in the safety margin (nucleation pH minus voiding pH) beyond baseline was 0.84 (95% CI 0.63-1.04), 0.57 (95% CI 0.37-0.78) and 0.41 (95% CI 0.20-0.61) for lemon juice, increased fluid intake and potassium citrate, respectively. A strong treatment effect on the safety margin was apparent even when controlling for study design (p <0.001).

CONCLUSIONS

Increased fluid intake with lemon juice may be a simple, inexpensive, effective strategy to control catheter encrustation.

Crystalline bacterial biofilm formation on urinary catheters by urease-producing urinary tract pathogens: a simple method of control

The problem of catheter encrustation stems from infection by urease-producing bacteria. These organisms generate ammonia from urea, elevate the pH of urine and cause crystals of calcium and magnesium phosphates to form in the urine and the biofilm that develops on the catheter. In this study, a laboratory model was used to compare the ability of 12 urease-positive species of urinary tract pathogens to encrust and block catheters. Proteus mirabilis, Proteus vulgaris and Providencia rettgeri were able to raise the urinary pH above 8.3 and produce catheter-blocking crystalline biofilms within 40 h. Morganella morganii and Staphylococcus aureus elevated the pH of urine to 7.4 and 6.9, respectively, and caused some crystal deposition in the biofilms but did not block catheters in the 96 h experimental period. Isolates of Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, Serratia marcescens, Pseudomonas aeruginosa and Providencia stuartii were only capable of raising the pH of urine to a maximum of 6.4 and failed to cause crystal deposition in the biofilm. The most effective way to prevent catheter encrustation was shown to be diluting urine and increasing its citrate concentration. This strategy raises the nucleation pH (pH(n)) at which calcium and magnesium phosphates crystallize from urine. Increasing the fluid intake of a healthy volunteer with citrated drinks resulted in urine with a pH(n) of >8.0 in which catheter encrustation was inhibited. It is suggested that this dietary strategy will be an effective means of controlling catheter encrustation, whichever bacterial species is causing the problem.

Stones and urinary tract infections

The term infection stones refers to calculi that occur following urinary tract infections (UTIs) caused by urease-producing gram-negative organisms. They consist of magnesium ammonium phosphate, carbonate apatite and monoammonium urate. Alkaline urine is most favorable to their formation. Urinary tract obstruction, neurogenic bladder, voiding dysfunction, temporary or indwelling urinary catheters, distal renal tubular acidosis and medullary sponge kidney are considered the main risk factors for developing infection stones. Urinalysis and urine culture are essential for diagnosis. A typical finding on imaging is a moderately radiopaque, staghorn or branched stone. Curative treatment is possible only by eliminating all of the stone fragments and by eradicating UTI. A variety of operative and pharmaceutical approaches is available. Metaphylactic treatment is mandatory to prevent recurrences. The relationship between urinary stones and UTIs is well known and shows two different clinical pictures: (1) stones that develop following UTIs (infection stones) which play a key role in stone pathogenesis, and (2) stones complicated by UTIs (stones with infection) which are metabolic stones that passively trap bacteria from coexistent UTIs and may consist of calcium or non-calcium. This article presents an overview of infection stones, analyzing the epidemiology, composition, pathogenesis, diagnosis, treatment and prevention of this type of calculi.

Modulation of crystalline Proteus mirabilis biofilm development on urinary catheters

The crystalline biofilms formed by Proteus mirabilis can seriously complicate the care of patients undergoing long-term bladder catheterization. The generation of alkaline urine by the bacterial urease causes calcium and magnesium phosphates to precipitate from urine and accumulate in the catheter biofilm, blocking the flow of urine from the bladder. The pH at which these salts crystallize from a urine sample, the nucleation pH (pH(n)), can be elevated by diluting the urine and by increasing its citrate content. The aim of this study was to examine whether manipulation of pH(n) in these ways modulated the rate at which crystalline biofilm developed. Experiments in laboratory models of the catheterized bladder infected with P. mirabilis showed that when the bladder was supplied with a concentrated urine (pH(n) 6.7) at a low fluid output (720 ml per 24 h), catheters blocked at 19-31 h. Diluting this urine 1:4 increased the pH(n) to 7.5 and models supplied with this urine at 2880 ml per 24 h took 110-137 h to block. When models were supplied with urine containing citrate at 1.5 mg ml(-1) or above (pH(n) 8.3-9.1), the catheters drained freely for the full 7 day experimental period. Scanning electron microscopy revealed that the catheter biofilms that developed in urine with high pH(n) values were devoid of crystalline formations. These observations should encourage a clinical trial to examine the effect of increasing a patient's fluid intake with citrate-containing drinks on the encrustation and blockage of catheters.

Preventive treatment of nephrolithiasis with alkali citrate—a critical review

Using the keywords "urolithiasis and citrate treatment", "nephrolithaisis and citrate treatment", "kidney stones and citrate treatment", a Medline search revealed 635 articles published between 1 January 1966 and 1 December 2004. For the present analysis, only studies meeting all of the following criteria were included: (1) publications in English or German, (2) studies on preventive alkali citrate treatment in patients with calcium oxalate, uric acid and infection stone disease, (3) clinical studies including at least ten subjects, and (4) treatment phases of at least 1 week duration. A total of 43 studies met the inclusion criteria and were further subclassified according to intermediate or ultimate endpoints as well as to study design. With stone recurrence as the ultimate endpoint, 21 uncontrolled studies in almost 1,000 patients demonstrated a reduction in stone forming rate by 47-100%. In four randomized controlled trials including 227 patients, 53.5% on alkali citrate vs 35% on placebo remained stone-free after at least 1 year of treatment (P<0.0005). Similar values (66% vs 27.5% for alkali citrate vs placebo, P<0.0005) were obtained in 104 patients from two randomized trials with dissolution/clearance of residual stones as endpoint. Unfortunately, up to 48% of alkali citrate treated patients left the studies prematurely, primarily due to adverse effects such as eructation, bloating, gaseousness or frank diarrhea.

Encrustation of biomaterials in the urinary tract

This review considers the problem of the encrustation of biomaterials used for urinary prostheses. After a general discussion of the problem it deals with exciting new developments which may prove to be clinically applicable in preventing this costly and resource consuming complication. The widespread use of use of in vitro models which accurately simulate the conditions found in the human urinary tract will allow appropriate preliminary studies. Perhaps then clinical evaluation will be warranted.

[Alkaline citrates in urology. A status report]

Alkaline citrates have been used as an efficient therapy in hypocitraturic calcium nephrolithiasis, uric acid lithiasis, cystinuria, and renal tubular acidosis. Furthermore, alkaline citrates are very effective in treating and preventing hyperchloremic metabolic acidosis in patients with urinary diversion. The main physiological effects during urolithiasis therapy have been significant increases in urinary pH, in citrate and potassium, and a decrease in calcium excretion. This paper reviews current indications, therapy modalities, and metaphylactic use reported in the literature and/or recommended by the Deutsche Gesellschaft für Urologie (DGU) and the European Association of Urology (EAU). It is intended to give useful advice for the urologist's daily practice.

Does fluid amount and choice influence urinary stone formation in persons with spinal cord injury?

OBJECTIVE

To examine the effects of fluid intake and beverage type on stone formation in persons with spinal cord injury (SCI).

DESIGN

A matched case-control study.

SETTING

A rehabilitation center within a university hospital.

PATIENTS

Forty-one patients with SCI who were diagnosed with urinary stones between 1992 and 1998 (stone cases) and 171 age- and duration-matched controls were interviewed by telephone.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Urinary stones.

RESULTS

Stone cases were more likely than controls to be white, to be current smokers, to be users of indwelling catheterization, and to have a lower body mass index (kg/m(2)), worse renal function, and higher urine specific gravity (P<.10). In a multivariable model that adjusted simultaneously for other possible risk factors, the greater consumption of juice (>207mL/d) was associated with a 70% decreased risk (odds ratio=0.3; 90% confidence interval, 0.1-1.0). An interesting, but not significant (P=.15), increased risk for coffee consumption was observed. There was no association for total fluid intake.

CONCLUSION

Total fluid intake does not appear to determine stone occurrence; however, fluid type may influence stone formation in persons with SCI. Further study is required to verify these findings, thus possibly leading to an effective fluid regimen for stone prophylaxis.

Uropathogens and urinary tract concretion formation and catheter encrustations

Infection stones (ammonium magnesium phosphate) and catheter encrustations have a common cause-urease producing microorganisms. With their rapid growth and frequent recurrences, infection stones are among the most troublesome of urinary system stones. For many patients with a long-term indwelling catheter, encrustations can be a severe problem. Urine composition is important, because, urine calcium enhances the crystallization process and urine citrate inhibits it. The role of non-urease producing microorganisms in stone forming processes is not well understood. Stones can now be successfully treated with a low morbidity index by percutaneous stone surgery or extracorporeal shock wave lithotripsy (ESWL) and recurrence of stone formation is then avoided by prolonged antibiotic treatment and oral citrate. Catheter encrustations and damage caused by ammonia released during urease activity can, however, be a serious problem in patients with indwelling catheters and our remedies are unsatisfactory.

Catheter-associated urinary tract infections

In the past few years it has been clearly demonstrated that the concept of bacterial biofilm production permits an understanding and provides some explanation of the pathogenesis, diagnosis and treatment of catheter-associated urinary tract infections. This concept describes the colonization of catheter surfaces and the movement of bacteria against the urinary flow. It explains the antibacterial resistance of these matrix-enclosed sessile populations of bacteria. The catheter encrustation can be observed as mineralizing bacterial biofilm. The differentiation in swarming cells exposing a much higher activity of the enzyme urease is responsible for the predominant role of Proteus mirabilis in obstructing encrustations. The guidelines for the prevention of catheter-associated urinary tract infections were developed over the past decades by clinicians and are still valid. They can now be better understood taking into consideration these new theories. As overuse of urethral catheters and non-compliance of their recommended use are still apparent, educational and surveillance programmes are needed to help maintain good standards of care.