Low-oxalate diet more beneficial than supplement

A preliminary analysis of data from a randomized controlled trial supports the efficacy of a low-oxalate diet for reducing urinary oxalate excretion in patients with idiopathic hyperoxaluria, but shows little or no benefit for daily dietary supplementation with vitamin B6 25 mg/magnesium 400 mg or a diet-supplement combination.

A definitive conclusion about the efficacy of the three interventions is pending the availability of outcomes from additional patients. At present, however, it is apparent that adherence is suboptimal with either dietary modification or supplement use and becomes extremely poor if patients are asked to follow both interventions, reported researchers at the 2017 World Congress of Endourology and SWL, Vancouver, BC.

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“To our knowledge, this is the first study designed to quantify and compare the effects of a dietary supplement, dietary changes, and both interventions for reducing urinary oxalate excretion, but evaluation of patient compliance with these treatments was a secondary objective,” said Mantu Gupta, MD, chair of urology at Mount Sinai West and Mount Sinai St. Lukes, New York.

Compliance findings ‘surprising’

“We know anecdotally that patients have a very hard time adhering to a low-oxalate diet, which is very restrictive and involves the elimination of a number of healthy foods. We hypothesized that compliance would be better with the supplement and reasoned that if it was as effective for reducing urinary oxalate excretion, the supplement could be a good alternative to diet for treating idiopathic hyperoxaluria in calcium oxalate stone formers. The findings that compliance was similar with the diet and the supplement and dropped dramatically among patients asked to do both were surprising, and the poor compliance explains why we do not yet have sufficient power to detect potentially statistically significant differences in efficacy between study groups,” Dr. Gupta said.

The study enrolled patients with calcium oxalate kidney stones who were newly diagnosed with idiopathic hyperoxaluria, defined as 24-hour urine oxalate excretion (Ox24) ≥40 mg. Patients were to follow their assigned treatment for 3 months before undergoing repeat Ox24 measurement.

At the time of the data analysis, 22 patients had been enrolled into the diet group, and the supplement and combination groups had each enrolled 21 patients. When the analysis was conducted, the proportion of patients who had completed the 3-month study and were evaluable for efficacy in the supplement, diet, and combination groups was 61.9%, 50.0%, and 19.0%, respectively. Some patients in each group had not yet reached the 3-month visit (14.3%, 9.1%, and 9.5%, respectively), but the others were not evaluable because of non-compliance (14.3%, 18.2%, and 38.1%, respectively) or loss to follow-up (9.5%, 22.7%, and 33.3%, respectively).

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“Many patients with idiopathic hyperoxaluria have other comorbidities. Asking them to add a dietary supplement may be easier than following a restrictive diet, and patients asked to do both may be compliant with the supplement only, thinking one intervention should be enough,” Dr. Gupta said.

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Analyses of data from completed patients showed no significant difference among the three groups in median starting Ox24 (range, 48.5 mg to 51 mg; p=.939). At 3 months, Ox24 was decreased from baseline by 21.4% in the diet group and by 4% in the supplement group, but had increased by 6.4% in the combination group (p=.121).

William Atallah, MD, MPH, endourology fellow, and Stephanie Purnell, MPH, research fellow, are collaborating with Dr. Gupta on the study. Purnell told Urology Times, “Since we performed our analysis to present our findings at the meeting, two more patients in the diet group and one additional patient in the supplement group completed the study. The direction of our results remains the same, however, after including their data.”

The authors are aiming to accumulate 20 completing patients in each group before conducting a final analysis.