A Caveat About Sodium Phosphate Enemas and Laxatives

How safe is the use of sodium phosphate enemas and laxatives in elderly persons?

In an age of polypharmacy, a variety of medications may result in constipation. One group particularly prone is the elderly, especially those in extended-care facilities. A durable remedy has been sodium phosphate, both as enemas and as oral purgatives. A number of adverse outcomes with these agents suggest that the medical community exercise caution in the future.

POTENTIALLY LETHAL COMPLICATIONS OF SODIUM PHOSPHATE ENEMAS

A recent one-center report details some serious and occasionally fatal complications as a consequence of sodium phosphate enemas.¹ Eleven elderly patients received sodium phosphate enemas for constipation. A standard dose is 250 mL. Eight of the 11 were given a standard dose; 3 others received between 500 and 798 mL total volume of the enema solution.

For the majority, difficulties began 24 hours after administration of the enema with hypotension, volume contraction, and striking rises in serum phosphate values (5.3 to 45 mg/dL) accompanied by severe hypocalcemia (2.0 to 8.7 mg/dL). Additional complications included hypernatremia, hypokalemia, hyperkalemia, metabolic acidosis, prolonged QTc interval, and a grand mal convulsion.

Hemodialysis was initiated in two of the patients in this group. All patients in this series experienced acute renal failure; five patients, or 45% of the cohort, died as a result. One autopsy was performed. That individual had calcifications comprised of calcium phosphate within renal tubular lumens.

RISK OF LARGE-SCALE FLUID ABSORPTION

Phosphate enemas are highly osmotic and stimulate fluid movement into the distal bowel within minutes of instillation. If the enema fluid is not expelled, systemic absorption of large volumes of fluid, sodium, and phosphate can occur. If a patient is ingesting anticholinergic medications, the absorption of the enema and its accompanying volume are more likely. Repeated enemas only exacerbate this potentially fatal syndrome. When this syndrome is diagnosed, aggressive fluid resuscitation and hemodialysis are necessary.

ADVERSE EFFECTS OF ORAL SODIUM PHOSPHATE

The single-center study motivated this author to search for other reports regarding the use of sodium phosphate enemas or laxatives. One series reported 37 cases of renal biopsy–proven acute phosphate nephropathy as a result of sodium phosphate solutions administered as oral purgatives.² Risk factors for complications with oral use of sodium phosphate included older age, female gender, use of angiotensin-converting enzyme inhibitors, hypertension, chronic renal disease, and diuretics.

This article reported that oral sodium phosphate solution had been removed from the market, but that tablets are still available. In terms of efficacy of bowel cleansing for colonoscopy, polyethylene glycol (PEG at 2 dosage strengths) and PEG with bisacodyl are better than sodium phosphate anyway.³

These reports should stimulate a change in practice patterns for those who administer sodium phosphate solutions, especially in patients who have any of the risk factors reviewed above.