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Osmotic / Stimulant Rectal Laxative Pregnancy: Caution — use only for acute constipation when safer options (macrogol, glycerol suppositories) have failed. Single dose considered acceptable; avoid repeated use.

Sodium Acid Phosphate Enema

Brand names: Fleet Ready-to-Use Enema, Phosphate Enema BP

Adult dose

Dose: 128mL (1 standard enema) rectally. Retain for 2–5 minutes if possible before evacuating. May repeat once after 30 minutes if no result.
Route: Rectal
Frequency: Single dose (repeat once if no effect after 30 minutes)
Max: 128mL per dose (1 enema); 256mL total per episode
Contains sodium dihydrogen phosphate and disodium hydrogen phosphate. Acts as osmotic and mild irritant — draws water into rectum and stimulates evacuation within 2–5 minutes. Used for rapid bowel clearance: acute constipation, pre-procedure bowel preparation, faecal impaction, and pre-operative bowel emptying. CAUTION in renal impairment — risk of severe hyperphosphataemia.

Paediatric dose

Route: Rectal
Frequency: Single dose
Max: Half adult dose (64mL) for children 7–11 years
BNF for Children: children <3 years — seek specialist opinion (risk of hyperphosphataemia and electrolyte disturbance). 3–6 years: use with extreme caution — specialist only. 7–11 years: 64mL (half adult dose). 12–17 years: adult dose (128mL). Source: BNF for Children 2024.

Dose adjustments

Renal

Avoid if eGFR <30 — significant risk of life-threatening hyperphosphataemia, hypocalcaemia, and cardiac arrhythmia.

Hepatic

No dose adjustment required.

Clinical pearls

  • Renal impairment is an absolute contraindication — even a single standard phosphate enema has caused fatal hyperphosphataemia with tetany and cardiac arrest in patients with eGFR <30. Always check renal function.
  • Acts within 2–5 minutes — warn the patient to remain close to a toilet after administration.
  • Pre-colonoscopy: phosphate enemas are used as a distal bowel prep adjunct. Do not use as sole preparation — combine with macrogol oral preparation for full bowel clearance.
  • Paediatric caution: children are at higher risk of electrolyte disturbance proportional to size — limit dose and frequency strictly.

Contraindications

  • Severe renal impairment (eGFR <30) — fatal hyperphosphataemia reported
  • Congestive heart failure (sodium load)
  • Ascites or severe fluid overload
  • Bowel obstruction or perforation
  • Inflammatory bowel disease (active — risk of worsening)
  • Imperforate anus

Side effects

  • Hyperphosphataemia (most dangerous — especially in renal impairment; can cause hypocalcaemia, tetany, and cardiac arrest)
  • Hyponatraemia / hypernatraemia (electrolyte shifts with repeated use)
  • Rectal irritation and discomfort
  • Abdominal cramping
  • Nausea

Interactions

  • No direct drug interactions, but electrolyte changes (hyperphosphataemia, hypocalcaemia) may affect cardiac drugs (digoxin — hypocalcaemia increases toxicity)

Monitoring

  • Serum phosphate and calcium (if renal impairment or repeated use)
  • Serum electrolytes (sodium, potassium)
  • Renal function (check eGFR before use)

Reference: BNFc; BNF 90; BNF for Children 2024; MHRA Safety Alert — Phosphate Enemas in Renal Impairment; SPC Fleet Enema. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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