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Sodium phosphate enemas increases risk of long-term kidney injury

The use of sodium phosphate enemas increases the risk of long-term kidney injury, according to a new study published in the National Kidney Foundation’s American Journal of Kidney Diseases.

The research discovered that the use of sodium phosphate enemas versus Polyethylene Glycol (PEG) prior to colonoscopy screening in Veterans Affairs patients increases the risk for having long-term estimated glomerular filtration rate (eGFR) decline. Additionally, patients with non-iron deficient anemia are at particularly high risk for eGFR decline.

“Sodium phosphate enemas are associated with a 38% increase in the chance of developing a decline in kidney function one year following the exposure,” said Monica Schaefer, Pharm.D., of the Department of Veterans Affairs. “Our research recommends that the use of sodium phosphate enemas be limited due to the risk of long-term impact on kidney function”

Sodium phosphate enemas have been used for the treatment of constipation and to enhance bowel preparation for procedures. The enema is comprised of sodium and phosphate and acts by pulling water into the gastrointestinal tract. The amount of phosphate used in the enema can potentially be absorbed into the blood and can cause elevated blood phosphorus levels. Polyethylene glycol solution is a solution of electrolytes. In contrast to sodium phosphate enemas, PEG has been designed to result in no net fluid increase or loss for the patient.

“The clinical implications from this study extend beyond avoiding the use of sodium phosphate enemas as part of bowel preparation for colonoscopy,” said Amina Khan, MD, of the Kansas City VA Medical Center. “We believe the results of our study are applicable to patients who are undergoing other procedures and the prescription of sodium phosphate should be avoided.”

The study was isolated to 70,499 Veterans over the age of 50 as guidelines recommend colonoscopy screening for that age group. Patients received sodium phosphate enemas (with or without PEG) or PEG alone prior to colonoscopy screenings. A 50% increase in serum creatinine level over a 15-month, over a 6-week, and between a 9- and 15-month period was used to define any, acute, or long-term eGFR decline, respectively. Multivariable logistic regressions estimated the likelihood of eGFR decline conditional on the use of sodium phosphate enemas versus PEG alone, controlling for potential confounders.

“The use of sodium phosphate enemas for medical procedures and treatments is a widespread practice,” said Thomas Manley, Director of Scientific Activities at the National Kidney Foundation. “Studies like this are crucial in cautioning medical professionals about the risks associated with prescribing this regimen as it can have an enduring negative impact on kidney function.”

While we can be certain that there is a significant level of kidney injury in the long-term, the exact mechanism is not known. The initial kidney injury is likely caused by transient hyperphosphatemia in the setting of volume depletion, but the mechanism of ongoing kidney injury leading to chronic kidney disease has not yet been defined.

“This study brings up additional interesting research questions and highlights the ongoing need for further research in the area of phosphate-related nephropathy,” said Dr. Khan. “The actual mechanism which led to a long-term decline in kidney function in our study needs to be identified in addition to the further study of phosphate enemas in a younger population.”

This study was the culmination of the work associated with Dr. Emily Littrell’s pharmacy residency project at the Kansas City VA. Dr. Schaefer, Pharmacoeconomics Program Manager and Residency Program Director at the VA Heartland Network, served as Dr. Littrell’s primary research mentor. Dr. Patterson, faculty at University of Missouri-Kansas City School of Pharmacy, served as a secondary research mentor. Dr. Amina Khan, Staff Nephrologist and Interim Section Chief for Nephrology at the Kansas City VA Medical Center served as the clinical expert.