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Oral Sodium Phosphate Renal Risks

According to new information reported to the U.S. Food & Drug Administration (FDA), oral sodium phosphate (OSP) drugs increase the risk of acute phosphate nephropathy in females and those with low body weight. These findings are important because the current labeling on OSP products does not indicate a difference in risk factors between men and women. Oral sodium phosphates are used to clean the colon prior to undergoing a colonoscopy procedure.

What’s the problem?

A retrospective study conducted by researchers at NorthShore University Health System in Evanston, Illinois has analyzed the renal risks of oral sodium phosphate tablets. The study, which was titled Renal risks of sodium phosphate tablets for colonoscopy preparation: A review of adverse drug reactions (ADRs) reported to the Food and Drug Administration (FDA), found that renal adverse drug reactions from sodium phosphate tablets are more common in females, with a mean body weight lower than the national average weight. Popular OSP products include OsmoPrep, Visicol and Fleet-Phospho Soda, which was been pulled from the U.S. market in December 2008.

Researchers extracted more than two million files from the FDA’s Adverse Event Reporting System (AERS) from 2004 to 2009, and found that 178 cases from tablet preparations (71 % females) were identified with increasing numbers of renal adverse drug reactions each year. “Using computer simulation, and subsequent single-dose pharmacokinetic analysis with Fleet’s Phospho-soda, our group demonstrated that individuals (especial females) of lower body weight developed marked elevation in serum phosphate levels following ingestion of the preparation.”

Taking these figures into consideration, the group that conducted the study recommends avoidance of OSPs in women, particularly those of smaller weight and stature. Additional studies are needed to confirm this association and establish causality.

OSPs and Acute Phosphate Nephropathy

Acute phosphate nephropathy is characterized by damage to the kidneys caused by the formation of phosphate crystals within the renal tubes. The condition is commonly associated with the ingestion of oral sodium phosphate bowel purgatives prior to colonoscopy procedures. In addition to sex (female) and low body weight, the risk for acute phosphate nephropathy is increased with age, dehydration, or in the presence of hypertension or if the patient is taking an ACE inhibitor or angiotensin receptor blocker. Signs and symptoms may include (but are not limited to):

  • abnormal heartbeat
  • bloating
  • difficult urination
  • epilepsy
  • general discomfort and fatigue
  • high blood pressure
  • lower back pain
  • muscle twitches and cramping

OSP Side Effects

In addition to the increased risk of acute phosphate nephropathy, OSPs like Visicol and OsmoPrep have been linked to the following side effects:

  • abdominal bloating & pain
  • headache
  • nausea
  • severe kidney damage
  • hyperphosphatemia
  • hypokalemia
  • hyperphosphatemia
  • renal failure
  • facial swelling
  • rash
  • pruritus
  • throat tightness
  • bronchiospasm

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