Is a single‑dose 118 mL Fleet (sodium phosphate) enema appropriate for rapid relief of occasional constipation in an adult, and what are its contraindications?

Fleet Enema for Occasional Constipation in Adults

A single 118 mL Fleet (sodium phosphate) enema can provide rapid relief of occasional constipation in carefully selected low-risk adults, but it carries significant risks of fatal hyperphosphatemia and should be avoided in elderly patients, those with renal impairment, and anyone with bowel motility disorders. 1, 2, 3

When Fleet Enema Is Appropriate

Fleet enema should be reserved as a rescue intervention only after oral laxatives have failed for several days. 1 The typical adult dose is 118–133 mL administered rectally, with bowel activity beginning within 30–60 minutes and lasting 2–4 hours. 4

Mechanism and Efficacy

• Sodium phosphate enemas work by creating an osmotic gradient that draws water into the bowel, distending the rectum, stimulating peristalsis, and lubricating stool to encourage evacuation. 1
• These enemas should be used sparingly with awareness of possible electrolyte abnormalities, particularly hyperphosphatemia and hypocalcemia. 1

Absolute Contraindications (Must Screen Before Use)

Hematologic Contraindications

• Never use in patients with neutropenia or thrombocytopenia due to risk of rectal bleeding, infection, bacteremia, or intramural hematoma. 1

Renal Contraindications

• Absolutely contraindicated in renal insufficiency, dialysis patients, or existing electrolyte disturbances because of the danger of fatal hyperphosphatemia and hypocalcemic coma. 1, 4, 2, 5
• In one case series, all 11 elderly patients who received Fleet enemas developed acute renal failure, with extreme hyperphosphatemia (phosphorus 5.3–45.0 mg/dL) and severe hypocalcemia (calcium 2.0–8.7 mg/dL), resulting in 45% mortality. 3
• Limit to once daily maximum in patients at any risk for renal dysfunction; optimally, use alternative agents. 1, 4

Gastrointestinal Contraindications

• Absolute contraindications include bowel obstruction, paralytic ileus, toxic megacolon, severe colitis, or unexplained abdominal pain. 1, 4
• Avoid in patients with small intestinal disorders or poor gut motility, as retention increases absorption and toxicity risk. 2, 5, 6
• Do not use in patients with recent colorectal or gynecologic surgery, recent anal/rectal trauma, or recent pelvic radiotherapy. 1, 4

Cardiovascular Contraindications

• Contraindicated in congestive heart failure, cirrhosis, or ascites due to sodium and water retention risks. 4

High-Risk Populations Requiring Alternative Enemas

• Elderly patients are at markedly increased risk for phosphate intoxication due to decreased glomerular filtration rate, polypharmacy, and comorbidities—prefer isotonic saline enemas instead. 1, 4, 5, 3
• Patients on ACE inhibitors, NSAIDs, or diuretics should receive alternative preparations such as isotonic saline. 4

Safer Alternative Enema Options

For General Bowel Preparation in High-Risk Adults

• Normal saline enema (500–1000 mL) gently distends the rectum and moistens stool with minimal mucosal irritation and no electrolyte disturbance. 1, 4

For Fecal Impaction

• Osmotic micro-enema (sorbitol-based, sodium citrate + glycerol) in small volume works best when the rectum is full on digital rectal exam. 1, 4
• Warm oil retention enema (120–180 mL cottonseed or olive oil, retained ≥30 minutes) provides lubrication and stool softening. 1, 4

For Stimulating Motility

• Bisacodyl enema (10 mg in 37 mL) stimulates peristalsis but may cause cramping. 4

Clinical Algorithm for Constipation Management

Step 1: Oral Laxatives First-Line

• Start with polyethylene glycol (PEG) 17 g twice daily or senna/bisacodyl as first-line therapy. 1, 7
• Maintain adequate fluid intake and encourage physical activity. 1

Step 2: Assess for Complications if Oral Therapy Fails

• Perform digital rectal examination to rule out fecal impaction. 1, 7
• Rule out bowel obstruction, hypercalcemia, hypothyroidism, or other constipating medications. 1, 7

Step 3: Rectal Interventions Only After Oral Failure

• If impaction is present: glycerin or bisacodyl suppository as first-line rectal therapy. 7, 4
• If no impaction but persistent constipation after several days: consider small-volume enema—but use saline or tap water enema in elderly or high-risk patients, not Fleet. 1, 4

Monitoring and Safety Measures

• Check serum phosphate and calcium in elderly patients or those with repeated enema use, especially if retention time is prolonged. 4
• Do not combine sodium phosphate enemas with antimotility agents or administer simultaneously with bisacodyl, as this causes severe cramping and compounded electrolyte disturbances. 4
• Following an educational campaign in one hospital, Fleet enema use was reduced by 96% after recognition of its 3.9% mortality rate in elderly constipated patients. 8

Critical Pitfalls to Avoid

• Do not use Fleet enema as first-line therapy—enemas are reserved for cases where oral laxatives have failed after several days. 1, 4
• Never administer to elderly patients or those with any degree of renal impairment—case reports document fatal hyperphosphatemia even with standard 118–250 mL doses. 2, 5, 3
• Avoid in neutropenic or thrombocytopenic patients due to infection and bleeding risk from rectal trauma. 1
• Do not exceed once daily dosing in any patient, and preferentially choose alternative enema preparations (saline, tap water) in all but the lowest-risk adults. 1, 4
• Perforation, hyperphosphatemia, and sepsis may cause death in up to 4% of cases when enemas are used for acute constipation, especially in the elderly. 8