In some patients bowel cleansing with an oral sodium phosphate solution (OSPS) may precipitate renal failure, investigators reported. "Acute phosphate nephropathy is an under-recognized cause of acute and chronic renal failure," wrote Glen S. Markowitz, M.D. of the Columbia College of Physicians and Surgeons.

They reported on 21 patients who developed acute phosphate nephropathy after taking an OSPS (Visicol). Four of the patients went on to require permanent hemodialysis, and the remaining 17 developed chronic renal insufficiency.

The cases occurred more frequently among patients older than 50, and may be associated with inadequate re-hydration while performing bowel cleansing, a history of hypertension, and concurrent use of an ACE inhibitor or angiotensin receptor blocker, the investigators found.

The condition appears to be a variant of nephrocalcinosis, which is marked by precipitation of calcium phosphate in the tubules of the kidney, leading to renal insufficiency. Nephrocalcinosis is usually linked to hypercalcemic conditions, and only rarely to excess phosphate intake, they noted.

The investigators had previously reported five cases of renal failure occurring after bowel cleansing with an OSPS. The current series followed 21 of 31 patients with nephrocalcinosis who were among 7,349 who had biopsies of their native kidneys.
The 21 patients who presented with acute renal failure all had normal serum calcium levels, and all had recently undergone colonoscopy preceded by bowel cleansing with an OSPS.

The patients ranged in age from 39 to 82 (mean 64), and the cohort was predominantly white and female. In all, 16 of the 21 patients had a history of hypertension, and 14 of these patients were taking either an ACE inhibitor or an angiotensin receptor blocker. In 19 patients for whom creatinine levels within four months of colonoscopy were available, the mean baseline serum creatinine was 1.0 mg/dl.

At the time of presentation with acute renal failure, the mean creatinine was 3.9 mg/dl at a median of one month after colonoscopy. "In a few patients, acute renal failure was discovered within three days of colonoscopy, at which time hyperphosphatemia was documented," the authors noted. "Patients had minimal proteinuria, normocalcemia, and bland urinary sediment."

At mean follow-up of 16.7 months, four of the patients went on to develop end-stage renal disease, requiring renal replacement therapy, including one successful kidney transplant.

Of the remaining 17 patients the mean serum creatinine at the end of follow-up was 2.4 mg/dL (range 1.3 to 3.4 mg/dL), and 16 had an improvement in renal function.

"Although the improvement in renal function is noteworthy, only four patients have reached a serum creatinine less than 2.0 mg/dL and no patient has returned to baseline," Dr. Markowitz and colleagues wrote.

Renal biopsies in these patients showed mild to diffuse tubular injury, diffuse calcium phosphate deposits, tubular atrophy and interstitial fibrosis (occurring in 19 of 21 patients), minimal to moderate interstitial inflammation, and evidence of mild to severe vascular nephropathy in all but one patient.

"OSPS is widely regarded as a safe agent for bowel cleansing before colonoscopy," the authors wrote. "Although transient hyperphosphatemia occurs, it is not associated with untoward events in the majority of patients. Factors that may predispose patients to acute renal failure after OSPS include inadequate hydration, increased patient age, hypertension with histologic evidence of arterionephrosclerosis, concurrent treatment with ACE inhibitors or angiotensin receptor blockers, or inappropriate use of OSPS in patients with chronic kidney disease or electrolyte disorders."

Although the majority of patients in this study were women, the sample size was not large enough to determine whether gender or some related factor such as body size might also be a risk factor, the investigators wrote.

Their findings suggested that colonoscopy guidelines may need to be revised to take into account the association between OSPS use and nephropathy, and to recommend avoiding OSPS use in patients with chronic kidney disease, they added.

· In patients scheduled for colonoscopy, the use of an oral sodium phosphate solution may be associated with acute phosphate nephropathy, especially among older patients and those with hypertension who are taking ACE-inhibitors or angiotensin receptor blockers.

· Hypertension, use of ACE-inhibitors or angiotensin receptor blockers was common in patients who developed renal failure however the etiologic role of these factors cannot be established by this case series study because it lacks a control group.

· Consider acute phosphate nephropathy in patients with acute renal failure or worsening of chronic renal insufficiency who recently underwent colonoscopy.

Source: Diabetes In Control: Markowitz GS et al. Acute Phosphate Nephropathy following Oral Sodium Phosphate Bowel Purgative: An Underrecognized Cause of Chronic Renal Failure. J Am Soc Nephrol. Published on September 28, 2005 as doi: 10.1681/ASN.2005050496 In the online edition of the Journal of the American Society of Nephrology.