A simple technique for assessing the propensity for crystallization of calcium oxalate and brushite in urine from the increment in oxalate or calcium necessary to elicit precipitation

Urine risk factors in children with calcium kidney stones and their siblings

Calcium nephrolithiasis in children is increasing in prevalence and tends to be recurrent. Although children have a lower incidence of nephrolithiasis than adults, its etiology in children is less well understood; hence, treatments targeted for adults may not be optimal in children. To better understand metabolic abnormalities in stone-forming children, we compared chemical measurements and the crystallization properties of 24-h urine collections from 129 stone formers matched to 105 non-stone-forming siblings and 183 normal, healthy children with no family history of stones, all aged 6 to 17 years. The principal risk factor for calcium stone formation was hypercalciuria. Stone formers have strikingly higher calcium excretion along with high supersaturation for calcium oxalate and calcium phosphate, and a reduced distance between the upper limit of metastability and supersaturation for calcium phosphate, indicating increased risk of calcium phosphate crystallization. Other differences in urine chemistry that exist between adult stone formers and normal individuals such as hyperoxaluria, hypocitraturia, abnormal urine pH, and low urine volume were not found in these children. Hence, hypercalciuria and a reduction in the gap between calcium phosphate upper limit of metastability and supersaturation are crucial determinants of stone risk. This highlights the importance of managing hypercalciuria in children with calcium stones.

Intestinal and renal effects of low-volume phosphate and sulfate cathartic solutions designed for cleansing the colon: pathophysiological studies in five normal subjects

OBJECTIVES

Ingestion of a concentrated low-volume phosphate solution produces copious diarrhea, which cleanses the colon, but it occasionally causes renal failure due to calcium phosphate precipitation in renal tubules. We hypothesized that a concentrated low-volume sulfate solution would be an equally effective cathartic, and that urine produced after sulfate would have less tendency to precipitate calcium salts than urine produced after phosphate.

METHODS

Hydrated subjects ingested 75 ml of phosphosoda or an equimolar dose of sulfate salts in a small volume of solution. Four liters of PEG (polyethylene glycol) lavage solution was the control. All solutions were administered in split doses, 10 h apart. Propensity of urine to precipitate at pH 6.4 (the pH of renal tubular fluid) was assessed by determining the minimal calcium concentration that caused precipitation.

RESULTS

Average diarrheal stool weight was 2,004 g after phosphate, 2,854 g after sulfate, and 3,021 g after PEG (P<0.001). Average calcium concentration (in mg/dl) required to induce urine precipitation at pH 6.4 was 43 after PEG, 10 after PO(4), and 187 after SO(4) (P=0.009).

CONCLUSIONS

(i) In equimolar doses, sulfate produced 42% more diarrheal stool weight than phosphate. (ii) Phosphate increased the propensity for calcium salt precipitation in urine at pH 6.4, whereas sulfate did not. (iii) These results suggest that a hypertonic low-volume sulfate solution would be an effective cathartic for colon cleansing and that sulfate-induced catharsis would be less likely than phosphate catharsis to produce calcium salt deposition in renal tubules.

Influence of grapefruit-, orange- and apple-juice consumption on urinary variables and risk of crystallization

Alkalizing beverages are highly effective in preventing the recurrence of calcium oxalate (Ox), uric acid and cystine lithiasis. The aim of the present study was to evaluate the influence of grapefruit-juice and apple-juice consumption on the excretion of urinary variables and the risk of crystallization in comparison with orange juice. All investigations were carried out on nine healthy female subjects without any history of stone formation and aged 26-35 years. Each juice was tested in a 5 d study. During the study, the subjects received a standardized diet. Fluid intake of 2.75 litres was composed of 2.25 litres neutral mineral water, 0.4 litre coffee and 0.1 litre milk. On the fourth and fifth day 0.5 litre mineral water was partly substituted by 0.5 or 1.0 litre juice under investigation respectively. The influence on urinary variables was evaluated in 24 h urine samples. In addition, the BONN risk index of CaOx, relative supersaturation (RS)CaOx crystallization was determined. Due to an increased pH value and an increased citric acid excretion after consumption of each juice, the RSCaOx decreased statistically significantly (P<0.05) for grapefruit juice, but not significantly for orange and apple juice. The BONN risk index yielded a distinct decrease in the crystallization risk. We showed that both grapefruit juice and apple juice reduce the risk of CaOx stone formation at a magnitude comparable with the effects obtained from orange juice.

Reduced crystallization inhibition by urine from women with nephrolithiasis

BACKGROUND

Human urine is known to inhibit growth, aggregation, nucleation, and cell adhesion of calcium oxalate monohydrate (COM) crystals, the main solid phase of human kidney stones. This study tested the hypothesis that low levels of inhibition are present in women with calcium oxalate stones and, therefore, could promote stone production.

METHODS

In 17 stone-forming women and 17 normal women matched in age within five years, inhibition by dialyzed urine proteins of COM growth and aggregation was examined, as well as whole urine upper limits of metastability (ULM) for COM and calcium phosphate (CaP) in relation to the corresponding supersaturation (SS).

RESULTS

Compared to normals, patient urine showed a reduced ULM in relation to SS. In contrast to men, there was no difference in growth inhibition.

CONCLUSIONS

Reduced CaP and CaOx ULM values in relation to SS are a characteristic of female stone formers. This defect could promote stones by facilitating crystal nucleation. Abnormal inhibition may well be a very important cause of human nephrolithiasis.

Reduced crystallization inhibition by urine from men with nephrolithiasis

BACKGROUND

Human urine is known to inhibit growth, aggregation, nucleation, and cell adhesion of calcium oxalate monohydrate (COM) crystals, the main solid phase of human kidney stones. This study tests the hypothesis that low levels of inhibition are present in men with calcium oxalate stones and could therefore promote stone production.

METHODS

In 17 stone-forming men and 17 normal men that were matched in age to within five years, we studied the inhibition by dialyzed urine proteins of COM growth, aggregation, and binding to cultured BSC-1 renal cells, as well as whole urine upper limits of metastability (ULM) for COM and calcium phosphate (CaP) in relationship to the corresponding supersaturation (SS).

RESULTS

Compared with normals, patient urine showed reduced COM growth inhibition and reduced ULM in relationship to SS. When individual defects were considered, 15 of the 17 patients were abnormal in one or more inhibition measurements. ULM and growth inhibition defects frequently coexisted.

CONCLUSIONS

Reduced COM growth and CaP and CaOx ULM values in relationship to SS are a characteristic of male stone formers. Both defects could promote stones by facilitating crystal nucleation and growth. Abnormal inhibition may be a very important cause of human nephrolithiasis.

Relationship between supersaturation and calcium oxalate crystallization in normals and idiopathic calcium oxalate stone formers

BACKGROUND

In an earlier study on recurrent CaOx stone formers with no detectable abnormalities, we found that the urine of these subjects had a lower tolerance to oxalate load than controls and that the removal of urinary macromolecules with a molecular weight greater than 10,000 D improved their tolerance to oxalate.

METHODS

The effects on CaOx crystallization of reduced urinary supersaturation of calcium oxalate (CaOx), induced by night water load, were studied in 12 normal males and in 15 male OxCa stone formers who were free from urinary metabolic abnormalities. The effect of the macromolecules, purified and retrieved from the natural and diluted urine, were analyzed in a metastable solution of CaOx.

RESULTS

The water load caused an increase in urine volume (from 307 +/- 111 to 572 +/- 322 ml/8 hr, P = 0.014 in normal subjects, and from 266 +/- 92 to 518 +/- 208 ml/8 hr, P = 0.001 in the stone formers) and a concomitant reduction of the relative CaOx supersaturation (from 8.7 +/- 2.5 to 5.1 +/- 2.5 ml/8 hr, P = 0.001 in normal subjects, and from 10.4 +/- 3.5 to 5.0 +/- 2.7 ml/8 hr, P = 0.001 in the stone formers). The decrease in CaOx supersaturation was accompanied by an increase of the permissible increment in oxalate, both in normal subjects (from 43.8 +/- 10.1 to 67.2 +/- 30. 3 mg/liter, P = 0.018) and in the stone formers (from 25.7 +/- 9.4 to 43.7 +/- 17.1 mg/liter, P = 0.0001), without any significant variations of the upper limit of metastability for CaOx (from 21.6 +/- 5.3 to 20.5 +/- 4.2 mg/liter in normal subjects, and from 18.7 +/- 4.5 to 17.1 +/- 3.7 mg/liter in the stone formers). The inhibitory effect of urinary macromolecules with molecular weight greater than 10,000 Daltons did not undergo any change when the latter were recovered from concentrated or diluted urine, either in normal subjects or in the stone formers.

CONCLUSIONS

Reduced CaOx supersaturation by means of water load has a protective effect with regards to CaOx crystallization in subjects who do not present any of the common urinary stone risk factors.

Dependence of upper limit of metastability on supersaturation in nephrolithiasis

Formation of renal stones requires supersaturation (SS) high enough to induce crystallization; such a SS is referred to as the upper limit of metastability (ULM). The ULM for calcium oxalate (CaOx) or calcium phosphate can be measured by adding oxalate or calcium to urine, respectively, and noting the point at which overt crystallization occurs as evidenced by clouding. In principle, the urine should be more prone to form stone crystals as its SS approaches the ULM, and the SS ULM distance has been used as an index of stone forming potential. In addition, one would expect the ULM and initial SS to be unrelated, as the starting urine SS has no apparent link to the amount of calcium or oxalate that urine can dissolve without leading to crystal formation. However, in rats, we have found a surprising correlation between ULM and SS, such that ULM appears to rise with initial SS, for CaOx, and, to a lesser extent, for brushite (Br), a typical calcium phosphate initial phase. In this study, we measured CaOx and Br ULM, and SS, in urine of 50 patients and 11 normal people, to determine if ULM and SS were correlated, as in rats, and to explore the relationship between SS and ULM. We found the same dependence of ULM on SS as in rats, for both CaOx and Br, and found no differences between patients and normal people with respect to this dependency. However, for Br, patients showed a lower ULM than normals, but the same initial SS, meaning that patients were closer to their crystal formation threshold than normals. Treatments for stones had no apparent effect on the SS-ULM dependency. We conclude that in humans, as in rats, ULM is related to initial SS, and that this relationship is the same in patients as in normals for CaOx, but shifted in a stone forming direction for Br among patients. The ULM-SS interaction is unaffected by contemporary conventional stone treatments, and is more marked for CaOx than Br. The mechanisms of the dependence are unknown. The smaller difference between ULM and initial SS for Br in patients than normal supports prior evidence suggesting a defect in stone patients that could lead to calcium phosphate crystallization, subsequent nucleation of CaOx, and stone disease.

Relationship between supersaturation and crystal inhibition in hypercalciuric rats

Calcium oxalate (CaOx) and calcium phosphate (CaP) crystals do not precipitate in large amounts in normal urine despite considerable supersaturation (SS), partly because urine inhibits crystal nucleation, aggregation, and growth. In normal rats and rats bred for hypercalciuria (GHS), we varied SS by varying calcium intake to test the hypothesis that increased SS might deplete inhibitors and reduce inhibition of crystal formation. In normal rats when compared to a low calcium diet (0.02% Ca), a high calcium diet (1.2% Ca) raised the SS of CaOx from 0.8 to 8.2. The high calcium diet also raised the upper limit of metastability (ULM) of CaOx (the SS at which crystals form in urine) from 11.8 to 36. In GHS rats, diet change altered CaOx SS from 1.5 to 12, and ULM from 17 to 50 (all differences, P < 0.001). Because ULM rose with SS, the increased SS had little potential to increase CaOx stone risk. For CaP, however, SS rose from 0.6 to 2.4 and 1.1 to 8 in normal and GHS rats (P < 0.001 for both), respectively, whereas ULM for CaP did not increase significantly (8 vs. 7 and 7 vs. 11; P = NS, both changes). Therefore, CaP SS rose close to the ULM, posing a high stone risk. The stones formed by these rats are composed of CaP. Increasing CaOx SS by diet raises ULM for CaOx thereby offsetting the risk of CaOx stones in rats.

Design of a suitable formulation of FK613, a novel antiallergic agent, based on its pharmacokinetic and pharmacodynamic properties in healthy subjects

The pharmacokinetic and pharmacodynamic properties of FK613, a novel indolyl piperidine derivative, were investigated after oral administrations of 5, 10 and 20 mg in hard gelatin capsules to healthy male volunteers. FK613 was rapidly and almost completely absorbed, and >89% was recovered in the urine as the unchanged form. The urinary excretion of FK613 was linearly correlated with plasma concentration and its low water solubility was the main concern regarding the safety. In another experiment using a double-blind crossover design, in which 0 (placebo), 5 and 20 mg FK613 were administered to determine the plasma concentration-effect relationship, suppression of the intradermal histamine-induced skin reaction by FK613 was observed. Thus, the maintenance of a plasma concentration of FK613 in the range of 80-250 ng center dot ml-1 was recommended to ensure the suppression of histamine-induced wheal by >50% and not to exceed the solubility in urine. To achieve this, a new hydrogel-type formulation of FK613 was developed, with the aim both of delaying its absorption, so as to suppress the sharp rise in plasma concentration, and of maintaining the effective concentration for a longer period of time. This formulation was administered after meals at the doses of 20, 30, 40, 50 and 60 mg, and at repeated doses of 40 mg twice daily for 6.5 days to evaluate the pharmacokinetics and safety in healthy subjects. The area under the plasma concentration curve increased linearly with dose, whereas maximum plasma concentration (Cmax) tended to peak as dose increased, indicating the desirable properties of this formulation. Although Cmax exceeded 250 ng/ml at doses of 30 mg or more, no urinary crystal formation was observed on careful inspection of urine.

Effects of urinary macromolecules on the nucleation of calcium oxalate in idiopathic stone formers and healthy controls

Urinary macromolecules have attracted great interest because of their possible role as both promoters and inhibitors of calcium oxalate (CaOx) crystallization and it remains unclear whether there is any difference, in their nucleating activity, between stone formers and controls. We selected 9 male idiopathic CaOx stone formers whose 24-h urines presented no evidence of common urinary stone risk factors such as hypercalciuria, hyperoxaluria, hyperuricosuria, hypocitraturia, hypomagnesiuria or low glycosaminoglycans excretion and 12 male controls (matched for age and body weight) whose 24-h urines did not differ from those of stone formers. The study of urinary CaOx nucleation was made in freshly voided overnight urines whose biochemical composition was almost identical in the two groups. In filtered (0.22 micron) and ultrafiltered (10 kDa) urine we performed an oxalate tolerance test to determine the permissible increment of oxalate, the oxalate level for nucleation and the permissible increment of CaOx relative supersaturation (CaOx RS). In filtered urine from stone formers the permissible increment of oxalate was lower than controls (30 +/- 10.2 vs. 46.7 +/- 9.7 mg/l, P = 0.001), the oxalate level for nucleation was lower (64.4 +/- 14.2 vs. 79.5 +/- 15.6 mg/l, P = 0.035) and the permissible increment of CaOx RS was also lower (9.71 +/- 2.59 vs. 13.39 +/- 3.62, P = 0.018). In ultrafiltered urine these differences disappeared because the removal of macromolecules in stone formers significantly enhanced the oxalate-tolerance values. The difference between the change of the oxalate permissible increment of filtered and ultrafiltered urine allowed a distinction to be made between stone formers and controls that was not feasible in other ways (7.6 +/- 5.3 vs. 3.3 +/- 5.9 mg/l, P < 0.0001). The study suggests that, in idiopathic CaOx stone formers free from common urinary risk factors of CaOx crystallization, there is an increased tendency for CaOx nucleation in urine, which is mediated by macromolecular components.

Calcium oxalate crystallization properties in urine with different specific electrical conductivities

The relationship between the degree of urine dilution and the risk of calcium oxalate crystallization was studied in 32 urine samples collected from stone formers and normal subjects during an 8-hour period between 10 p.m. and 6 a.m., and in 4-hour urine samples collected during 24-hour periods from 6 patients with calcium stone disease. The risk of calcium oxalate crystallization was analyzed in terms of the increase in oxalate concentration required for a standardized precipitation of crystals of calcium oxalate. The degree of urine dilution was determined with a new instrument (urimho) designed for measuring the concentration, in terms of specific electrical conductivity, in urine samples of droplet size. With this device urine concentration can be expressed in urimho values between 1 and 5. There was a good correlation between recordings of specific electrical conductivity performed with the new device and with a conventional conductivity meter. There was a statistically significant positive correlation between urimho values and calcium oxalate crystallization. Calcium oxalate crystallization greater than 1.3 was not observed in any sample with a urimho value of 2 but it was noted in 31% of the samples with urimho values greater than 2. A positive relationship was also recorded between the urine pH and the urimho level, which is noteworthy because there was an inverse relationship between urine pH and calcium oxalate crystallization. A pH greater than 6 was observed in 78% of the samples with a urimho value of 2 but it was noted in only 27% of the samples with urimho readings between 3 and 5. A considerable variation in the response in urinary flow to ingested volumes was recorded. Therefore, monitoring of urine dilution by means of a sample device like the urimho might be of great help for patients with calcium stone disease in an effort to prevent recurrent stone formation by urine dilution, provided a urimho value of less than 3 can be maintained.

Effects of urinary macromolecules on the crystallization of calcium oxalate

The macromolecular fraction of urine with a molecular weight above 3,000 was isolated by dialysis. In the dialysed urine the rate of calcium oxalate (CaOx) crystallization was reduced both in the presence and absence of CaOx seed crystals. There was a clear relationship between crystallization and the relative concentration of the dialysed urine, with the highest crystallization propensity at the lowest concentration of macromolecules. Dilution of dialysed urine also affected crystal size distribution, with a predominance of small (2.8-4.5 microns) crystals in 100% dialysed urine and of large (5.6-14.0 microns) crystals in 5% dialysed urine. This is consistent with a macromolecular inhibition of both crystal growth and aggregation. Analysis of the crystal size distribution 120 min after supersaturation of whole urine to a level at which approximately 100 crystals in the size interval 3.5-5 microns were detected in a Coulter counter surprisingly disclosed a higher mean crystal volume in urine samples from normal subjects than from stone formers. This gives support to the assumptions that macromolecules might be of importance during the initial phase of CaOx crystallization and that urine from stone formers and normal subjects might be different in this respect.

Modulation by calcium of the inhibitor activity of naturally occurring urinary inhibitors

The possibility that hypercalciuria could cause calcium stone formation through a mechanism other than by increasing urinary saturation of stone-forming calcium salts was explored. The effect of increasing calcium concentration on the inhibitor activity against the spontaneous precipitation of calcium oxalate was examined in whole urine (in the presence of naturally occurring inhibitors) and in synthetic media (with added inhibitors). In 11 patients with calcium nephrolithiasis, the induced hypercalciuria from calcium supplementation (600 mg/day) caused a significant fall in the urinary inhibitory activity against calcium oxalate precipitation, as shown by a decline in the formation product ratio from 12.6 +/- 1.1 SEM to 9.6 +/- 1.4 (P less than 0.005). In order to more fully explore this observation, the effect of increasing calcium concentration on the inhibitory activities of citrate (2 mM), chondroitin sulfate (0.05 mg/liter) and a heterogeneous group of naturally-occurring urinary inhibitors (1.0 mg/liter) against calcium oxalate precipitation was examined in vitro in synthetic solutions. The inhibitory actions of both citrate and chondroitin sulfate were significantly attenuated by increasing calcium concentration from 0.25 mM to 6.0 mM (P less than 0.01). However, raising the calcium concentration in synthetic media containing a mixture of partially purified urinary inhibitors produced a significant rise in the urinary inhibitory activity of this macromolecular mixture (P less than 0.01). We conclude that hypercalciuria can attenuate the inhibitory activities of citrate and chondroitin sulfate against calcium oxalate precipitation while at the same time accentuating the inhibitory activity of naturally-occurring urinary inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by citrate of spontaneous precipitation of calcium oxalate in vitro

Effect of citrate on the spontaneous precipitation of calcium oxalate was examined in synthetic media. Citrate significantly increased the formation product of calcium oxalate. This "direct" measure of inhibitor activity, representing activity product at the point of nucleation, rose by 76% by the addition of citrate sufficient to provide trivalent citrate concentration of 1.49 mM. Moreover, citrate inhibited calcium oxalate crystallization by complexing calcium and lowering calcium oxalate saturation. This "indirect" measure of inhibitor activity was assessed from the concentration product of calcium oxalate at the point of nucleation, since this measure should provide a reflection of both ion pair formation and direct inhibitor activity of citrate. The concentration product exceeded the formation product at all ionic (trivalent) citrate concentrations, particularly at high ionic citrate levels. At the ionic citrate concentration of 1.49 mM, the rise in the concentration product was 373%, which was nearly fivefold that observed for the formation product. The presence of ferric or aluminum cations at a physiologic concentration of 2 mg/l did not modify the increase in formation product produced by citrate. Thus, citrate inhibits calcium oxalate crystallization, largely by complexing citrate, but also by directly affecting nucleation. Presence of ferric or aluminum cations at a physiological concentration does not modify the inhibitor action of citrate.

Measurement of the risk of calcium phosphate crystallization in urine

A method is described for analysis of the risk of calcium phosphate (CaP) crystallization in urine samples. The pH required for formation of 500 crystals in the size range 3.5 to 5 micron (pHCaP) was determined in a Coulter Counter following addition of sodium hydroxide. The risk of CaP crystallization (CaP-CR) was defined as: 1/(pHCaP--5.8). CaP-CR was determined in 24 h urine collections from 25 patients with calcium stone disease and 26 normal subjects, each urine diluted to a creatinine concentration of 5 mumol per ml. The mean (+/- SD) CaP-CR was 0.71 +/- 0.18 and 0.63 +/- 0.14 respectively and did not differ significantly. This method might be useful for evaluations and follow-up of stone formers with respect to the risk of CaP precipitation and stone formation.

Successful management of uric acid nephrolithiasis with potassium citrate

Eighteen patients with uric acid nephrolithiasis (six with uric acid stones alone and 12 with both uric acid and calcium stones) underwent long-term treatment (1 to 5.33 years, mean of 2.78 years) with potassium citrate (30 to 80 mEq/day, usually 60 mEq/day). Urinary pH increased from low (5.30 +/- 0.31 SD) to normal (6.19 to 6.46) during treatment. Urinary content of undissociated uric acid, which was high to begin with at 204 +/- 82 mg/day, decreased to the normal range (64 to 108 mg/day) following treatment. Urinary citrate rose from 503 +/- 225 mg/day to 852 to 998 mg/day. Urinary saturation of calcium oxalate significantly declined with potassium citrate treatment. New stone formation rate declined from 1.20 +/- 1.68 stones/year to 0.01 +/- 0.04 stones/year (P less than 0.001 by chi square). Remission was experienced in 94.4% of patients, and the group stone formation rate declined by 99.2%. Detailed case reports were obtained in five patients showing different responses between sodium alkali and potassium alkali treatment. All five patients had persistently low urinary pH (typically less than 5.5) and normouricosuria, and four had hyperuricemia. Before treatment, they had stones surgically removed or spontaneously passed, which were pure uric acid in composition. When sodium alkali was give (as bicarbonate or citrate, 60 to 118 mEq/day), new stone formation continued in four patients, and a radiolucent (uric acid) calculus become "calcified" in the remaining patient. The stone analysis disclosed calcium oxalate in five patients and calcium phosphate in three patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term treatment of calcium nephrolithiasis with potassium citrate

The long-term effects of potassium citrate therapy (usually 20 mEq. 3 times daily during 1 to 4.33 years) were examined in 89 patients with hypocitraturic calcium nephrolithiasis or uric acid lithiasis, with or without calcium nephrolithiasis. Hypocitraturia caused by renal tubular acidosis or chronic diarrheal syndrome was associated with other metabolic abnormalities, such as hypercalciuria or hyperuricosuria, or occurred alone. Potassium citrate therapy caused a sustained increase in urinary pH and potassium, and restored urinary citrate to normal levels. No substantial or significant changes occurred in urinary uric acid, oxalate, sodium or phosphorus levels, or total volume. Owing to these physiological changes, uric acid solubility increased, urinary saturation of calcium oxalate decreased and the propensity for spontaneous nucleation of calcium oxalate was reduced to normal. Therefore, the physicochemical environment of urine following treatment became less conducive to the crystallization of calcium oxalate or uric acid, since it stimulated that of normal subjects without stones. Commensurate with the aforementioned physiological and physicochemical changes the treatment produced clinical improvement, since individual stone formation decreased in 97.8 per cent of the patients, remission was obtained in 79.8 per cent and the need for surgical treatment of newly formed stones was eliminated. In patients with relapse after other treatment, such as thiazide, the addition of potassium citrate induced clinical improvement. Thus, our study provides physiological, physicochemical and clinical validation for the use of potassium citrate in the treatment of hypocitraturic calcium nephrolithiasis and uric acid lithiasis with or without calcium nephrolithiasis.

Use of potassium citrate as potassium supplement during thiazide therapy of calcium nephrolithiasis

The effectiveness of potassium citrate as a potassium supplement was compared to that of potassium chloride in 13 patients with calcium nephrolithiasis treated with thiazide. Thiazide treatment alone reduced serum potassium, urinary calcium and citrate without affecting urinary pH. Urinary saturation of calcium oxalate and brushite decreased but not as much as the decrement in urinary calcium because of reduced citrate-calcium complexation. Potassium chloride supplementation averted thiazide-induced hypokalemia and hypocitraturia without influencing hypocalciuric action of thiazide or urinary pH. The decline in urinary saturation of calcium salts paralleled the decrement in urinary calcium. Potassium citrate supplementation also kept urinary calcium low and corrected hypokalemia. Moreover, it increased urinary pH and citrate above levels in other phases. Thus, the ability of thiazide to lower the urinary saturation of calcium oxalate was accentuated by potassium citrate supplementation but not by potassium chloride supplementation, probably owing to increased citrate complexation of calcium. Moreover, the potassium citrate therapy was more effective than potassium chloride supplementation in reducing the propensity for the spontaneous precipitation of calcium oxalate in urine. In conclusion, potassium citrate supplementation may be superior to potassium chloride supplementation in patients receiving thiazide in whom stones form.