What complications can arise from using Fleet's enema (sodium phosphate) in elderly patients with renal insufficiency, heart failure, hypertension, or who are taking diuretics, ACE inhibitors, or potassium‑sparing agents?

Fleet's Enema Complications in High-Risk Elderly Patients

Fleet's enema (sodium phosphate) is contraindicated in elderly patients with renal insufficiency, heart failure, or those taking diuretics, ACE inhibitors, or potassium-sparing agents due to life-threatening risks of severe hyperphosphatemia, hypocalcemia, acute kidney injury, and death. 1, 2

Life-Threatening Metabolic Derangements

Fleet's enema causes rapid systemic absorption of phosphate through the colonic mucosa, leading to a cascade of severe electrolyte abnormalities:

• Extreme hyperphosphatemia (phosphorus levels 5.3-45.0 mg/dL) occurs within 24 hours of administration, even with standard 250 mL doses 2
• Severe hypocalcemia (calcium levels as low as 2.0-8.7 mg/dL) develops as phosphate binds serum calcium, precipitating calcium-phosphate crystals in tissues 2, 3
• Hypocalcemic tetany and coma can occur rapidly, with prolonged QT intervals on ECG predisposing to fatal arrhythmias 3, 4
• Hypernatremia and hypokalemia compound the metabolic crisis in most patients 2, 5

The mortality rate in elderly patients who develop these complications approaches 45%, with survivors often requiring urgent hemodialysis 2.

Acute Phosphate Nephropathy

Acute kidney injury occurs in virtually all elderly patients who develop Fleet's enema toxicity, characterized by:

• Calcium-phosphate crystal deposition within renal tubular lumens, causing direct tubular obstruction and necrosis 2
• Slowly progressive renal insufficiency that may become irreversible, termed "acute phosphate nephropathy" 5
• Volume depletion and hypotension exacerbating renal injury 2, 3

This complication is particularly devastating because it can occur even with standard doses in at-risk patients 2, 5.

High-Risk Patient Populations (Absolute Contraindications)

The FDA label and clinical evidence identify the following as contraindications or extreme caution scenarios 1:

• Renal insufficiency of any degree: Elderly patients have age-related decreased glomerular filtration rate, and phosphate is substantially excreted by the kidney—impaired clearance leads to toxic accumulation 1, 3, 5
• Heart failure: Sodium phosphate solutions contain high sodium loads that precipitate volume overload and cardiac decompensation in patients with congestive heart failure 1
• Patients on diuretics: These patients are volume-depleted and have impaired renal perfusion, dramatically increasing phosphate absorption and reducing renal clearance 2, 5
• Patients on ACE inhibitors or ARBs: These medications reduce glomerular filtration pressure and impair phosphate excretion, while also predisposing to hyperkalemia when combined with the hypokalemia from Fleet's enema 6
• Patients on potassium-sparing diuretics: The combination creates competing risks—Fleet's causes hypokalemia while these agents cause hyperkalemia, and both impair renal function 6
• Bowel obstruction or poor gut motility: Prolonged mucosal contact time increases phosphate absorption 3, 5, 7
• Small intestinal disorders: Altered absorption kinetics increase systemic phosphate load 3, 5

Clinical Presentation and Timeline

Patients typically present within 24 hours with 2, 3:

• Hypotension and severe volume depletion
• Altered mental status progressing to coma
• Muscle cramps, tetany, or seizures (from hypocalcemia)
• Oliguria or anuria (acute kidney injury)
• Cardiac arrhythmias (prolonged QT, potential for torsades de pointes)
• Progressive abdominal distention and ileus 4

Safer Alternatives

Use tap water or normal saline enemas instead of sodium phosphate preparations in elderly patients or those with any of the above risk factors 3, 5. These alternatives:

• Do not cause systemic electrolyte disturbances
• Are equally effective for bowel cleansing
• Carry minimal risk even in high-risk populations

For bowel preparation before procedures, isosmotic polyethylene glycol (PEG) solutions are the preferred alternative in elderly patients and those with contraindications to sodium phosphate 5.

Critical Pitfalls to Avoid

• Never assume "standard dose" is safe: Even 250 mL doses have caused fatal complications in elderly patients with risk factors 2, 5
• Do not use Fleet's enema in any patient with creatinine >1.5 mg/dL or estimated GFR <60 mL/min: The FDA warns that elderly patients are more likely to have decreased renal function, and phosphate toxicity risk is substantially higher 1
• Avoid in patients taking multiple medications affecting renal function: The combination of ACE inhibitors, diuretics, and NSAIDs creates a "perfect storm" for acute phosphate nephropathy 6, 5
• Do not administer to patients with heart failure or edematous states: The sodium load (up to 19 grams in standard preparations) can precipitate acute decompensation 1

Institutional Safety Measures

Following educational campaigns about Fleet's enema risks, hospital use has been reduced by 96% in institutions that implemented safety protocols 2. Consider:

• Restricting Fleet's enema availability in geriatric units
• Requiring physician approval for use in patients >65 years
• Defaulting to tap water or saline enemas for routine constipation management
• Educating staff about the disproportionate risk in elderly patients with comorbidities