Sodium Picosulfate

Sodium picosulfate is a diphenylmethane stimulant laxative prodrug activated by colonic bacteria. It is used at low dose for constipation and, combined with magnesium oxide and citric acid, as a low-volume bowel preparation before colonoscopy or surgery.

Classification. Stimulant laxative; bowel cleansing agent.

Mechanism. Bacterial sulphatases in the colon convert it to the active metabolite bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM), which stimulates colonic peristalsis and increases fluid secretion. In bowel preparation, magnesium citrate adds an osmotic effect.

Pharmacodynamics. Laxative effect begins 6 to 12 hours after oral dosing. In bowel preparation, cleansing begins 1 to 3 hours after the first dose.

Pharmacokinetics. Minimally absorbed. Absorbed BHPM is conjugated and excreted in urine. The magnesium component is partly absorbed and excreted by the kidneys.

Adult doses unless stated.

Constipation.

• 5 to 10 mg orally at bedtime (drops or elixir; check the product strength).

• Use short courses; seek review if needed for more than 1 week.

Bowel preparation before colonoscopy, radiology or surgery.

• Combined sachet containing sodium picosulfate 10 mg, magnesium oxide and citric acid, each dissolved in about 150 mL of water.

• Split dose: the first sachet the evening before the procedure and the second sachet on the morning of the procedure, about 10 to 12 hours later.

• Take generous clear fluids with each sachet; the label sets the volume, commonly 2 litres or more in total.

• A low-residue diet is advised on the day before; stop solid food as directed and stop clear fluids at least 2 hours before the procedure.

Children.

• Constipation: age 4 to 9 years 2.5 to 5 mg at bedtime; age 10 to 17 years 5 to 10 mg at bedtime.

• Bowel preparation in children: specialist dosing by age and weight.

Kidney and liver adjustment.

• Constipation dose: no adjustment.

• Bowel preparation: avoid in severe kidney impairment (CrCl under 30 mL/min) because magnesium accumulates.

• Use with caution in liver disease and heart failure.

Contraindications. Intestinal obstruction or ileus; acute surgical abdomen; acute inflammatory bowel disease and toxic megacolon; severe dehydration; gastric retention; hypermagnesaemia; severe kidney impairment (bowel preparation); hypersensitivity.

Common adverse effects. Abdominal cramp, nausea, bloating, headache and sleep disturbance during bowel preparation.

Serious adverse effects.

• Hyponatraemia with seizures, particularly in older adults and in patients on SSRIs, diuretics or desmopressin.

• Dehydration, hypokalaemia and kidney injury.

• Hypermagnesaemia in kidney impairment.

• Ischaemic colitis, aspiration and arrhythmia due to electrolyte loss.

Major interactions.

• Antibiotics may reduce the effect by killing colonic bacteria that activate the drug.

• Oral medicines taken during the preparation may be flushed through unabsorbed; take essential medicines at least 1 hour before the first sachet.

• Tetracyclines, fluoroquinolones, iron, penicillamine and bisphosphonates: magnesium chelates; separate by 2 hours.

• Diuretics, NSAIDs, ACE inhibitors and angiotensin receptor blockers: risk of kidney injury and electrolyte disturbance.

• Drugs causing hyponatraemia (SSRIs, carbamazepine, desmopressin): additive risk.

• Digoxin and QT prolonging drugs: electrolyte loss increases arrhythmia risk.

Special groups.

• Pregnancy: avoid bowel preparation unless essential; constipation is better treated with macrogol first-line.

• Breastfeeding: low transfer; compatible with occasional use.

• Children: dose by age; bowel preparation under specialist direction.

• Older adults: higher risk of dehydration and hyponatraemia; consider admission for frail patients.

• Kidney impairment: avoid bowel preparation in severe impairment.

• Liver impairment: use with caution.

Formulations. Oral drops or elixir 5 mg in 5 mL; combined powder sachet (sodium picosulfate 10 mg with magnesium oxide and citric acid) for bowel preparation.

Administration.

• Dissolve the sachet in about 150 mL of cold water, stir for 2 to 3 minutes and drink when cool.

• Drink clear fluid as directed after each sachet.

• Constipation drops: take at bedtime with water.

Baseline. Kidney function and electrolytes in older adults, kidney disease, heart failure and patients on diuretics. Exclude obstruction.

Monitoring.

• Hydration, sodium and potassium in at-risk patients after bowel preparation.

• Stool pattern in constipation.

• Seizure, confusion or severe headache as signs of hyponatraemia.

Therapeutic drug monitoring. Not applicable.

Stopping. Stop constipation therapy if diarrhoea or cramps develop. Bowel preparation is a single course; do not repeat without review.

Referral and escalation. Seek urgent review for severe abdominal pain, distension, vomiting, rectal bleeding, confusion or seizure after bowel preparation. Colorectal referral for red flags: weight loss, rectal bleeding, iron deficiency anaemia or change in bowel habit over age 50.