ACP: New Guideline on Staving Off Stones
Published: Nov 3, 2014 | Updated: Nov 4, 2014
The American College of Physicians (ACP) has recommended in a new clinical guideline that patients who have had at least one kidney stone should increase their fluid intake and that pharmacotherapy may be given if increased fluid alone is inadequate to prevent stone recurrence.
In a recommendation classified as weak and with low-quality evidence, the guideline committee wrote, "ACP recommends management with increased fluid intake spread throughout the day to achieve at least 2 L of urine per day to prevent recurrent nephrolithiasis," according to Amir Qaseem, MD, PhD, director of the ACP's department of clinical policy, and colleagues.
And in a second recommendation, also classified as weak but with moderate-quality evidence, they stated in the Nov. 4 issue of Annals of Internal Medicine, "ACP recommends pharmacologic monotherapy with a thiazide diuretic, citrate, or allopurinol to prevent recurrent nephrolithiasis in patients with active disease in which increased fluid intake fails to reduce the formation of stones."
Kidney stones develop when substances that can form crystals are in high concentration in the urine, or when crystal-inhibiting substances are inadequate. In the majority of cases, the stones consist of calcium oxalate and/or calcium phosphate, although other substances also can be found in some cases, including uric acid, cystine, and struvite.
Lifetime prevalence among men is 13%, and about half that for women. After a first stone, the recurrence rate over 5 years can reach 50% in untreated patients.
"Efforts to prevent the recurrence of nephrolithiasis target decreasing concentrations of the lithogenic factors (for example, calcium and oxalate) and increasing the concentrations of inhibitors of stone formation (for example, citrate)," Qaseem and colleagues explained.
Dietary strategies to aid in this have included raising intake of liquids, reducing the consumption of animal protein and oxalates, and maintenance of normal calcium intake.
To review the available evidence for both diet and pharmacotherapy for the prevention of recurrent kidney stones, the committee members conducted a literature search through March 2014 to assess short-term stone outcomes and long-term clinical health outcomes. They also considered any potential harms of treatment, such as changes in weight, lipids, or glucose levels or adverse events such as nausea and diarrhea.
The recommendation on increased fluid intake was primarily based on a study that included 300 patients who were followed for 5 years after an initial stone episode. In this study, 12.1% of patients whose urinary output was 2 L or more had a recurrence compared with 27% of controls. A second study of patients followed for 2 to 3 years found recurrence rates of 8% with increased fluid intake versus 55.6% for controls.
Other evidence relating to fluid intake focused on mineral water and soda. A study that evaluated the effects of low mineral content Fiuggi water reputed to help flush out kidney stones found recurrences of 17% for the oligomineral water and 22.9% for tap water.
And a study of individuals who had previously drunk large quantities of soda but who then abstained found a recurrence rate of 33.7% compared with 40.6% for controls. This study also revealed that the decreased risk was only among individuals who drank colas, which are acidified with phosphoric acid, and not for those who favored fruit-flavored sodas acidified with citric acid.
Mixed results were seen when diets were considered. For instance, in one study that included low animal protein and purine and high bran and fiber, recurrences occurred in 24% of those who followed the diet compared with only 4.1% of those who were on a control diet.
Yet another study showed that a diet consisting of low animal protein and sodium and normal to high calcium was associated with a 20% recurrence rate compared with 38.3% for a control diet.
The guideline authors also looked for potential harms with fluid and diet strategies and found that there were few withdrawals from studies of fluid, but high rates in diet studies. There was little reporting of adverse events.
The second recommendation, dealing with pharmacotherapy, reflected the findings of 20 studies. Six of the studies involved comparisons of thiazide diuretics with placebo and found that the risk of recurrence was halved in the treatment groups (24.9% versus 48.9%).
Another group of studies compared monotherapy with citrate and placebo and again found benefits from the treatment, with recurrence rates of 11.1% compared with 52.3%. Allopurinol also was associated with reduced rates of recurrence (33.3% versus 55.4%).
Combination regimens of calcium oxalate plus thiazide or thiazide plus citrate showed no additional benefits compared with monotherapy.
Potential harms associated with pharmacotherapy included adverse events such as gastrointestinal problems, fatigue, orthostasis, headache, and anemia in some trials, although these were inconsistently reported.
Evidence was inadequate to determine the utility of interventions based on the composition of stones or urine/blood chemistries.
"Although biochemistry suggests a relationship between pharmacologic method of action and stone type, no randomized, controlled trials link biochemical testing to outcomes," the guidelines committee noted.
They also pointed out that almost all of the studies included in the review included only calcium stones.
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