Docusate Sodium

Docusate sodium is an anionic surfactant used as a stool softener. It is widely prescribed, particularly for opioid-induced constipation and to avoid straining, but its efficacy over placebo is weak and stimulant or osmotic laxatives work better.

Classification. Stool softener (emollient laxative); anionic surfactant.

Mechanism. Lowers surface tension at the oil and water interface, allowing water and fat to penetrate the faecal mass. It may also modestly increase intestinal fluid secretion.

Pharmacodynamics. Onset is slow, 12 to 72 hours after oral dosing and 2 to 15 minutes after a rectal dose. Effect on stool frequency is small.

Pharmacokinetics. Absorption from the gut is limited and variable. It is excreted mainly in bile and faeces.

Adult doses unless stated. Use is short term.

Constipation (oral).

• 100 mg twice daily; usual range 50 to 300 mg daily in one to three divided doses.

• Maximum 500 mg daily in divided doses.

• Reassess at 1 week; stop if there is no benefit.

Opioid-induced constipation. Docusate alone is not effective. Combine it with a stimulant laxative (senna or bisacodyl) or an osmotic laxative (macrogol), or use a stimulant alone.

Rectal use. Docusate microenema 120 mg once daily as needed for hard stool.

Paediatric dosing.

• Age 1 to 11 years: 12.5 to 25 mg three times daily using oral solution.

• Age 12 years and over: adult dose.

• Under 1 year: specialist advice.

Kidney and liver adjustment. None.

Contraindications. Intestinal obstruction; acute abdominal pain of undiagnosed cause; hypersensitivity.

Common adverse effects. Abdominal cramp, loose stool and throat irritation with liquid preparations (bitter taste).

Serious adverse effects.

• Rash and hypersensitivity (rare).

• Diarrhoea with dehydration and electrolyte loss at high doses.

• Increased absorption of liquid paraffin, with risk of lipoid pneumonia if aspirated.

Major interactions.

• Liquid paraffin (mineral oil): docusate increases its absorption; avoid combination.

• Other laxatives: additive effect.

Special groups.

• Pregnancy: acceptable for short use, although macrogol and bulk-forming laxatives are better supported.

• Breastfeeding: not expected to enter milk meaningfully; compatible.

• Children: oral solution dosed by age; macrogol is preferred.

• Older adults: no adjustment; monitor fluid intake.

• Kidney impairment: no adjustment.

• Liver impairment: no adjustment.

• Regional: widely available alone and in combination with senna.

Formulations. Capsules 50 mg and 100 mg; oral solution 12.5 mg in 5 mL; microenema 120 mg.

Administration. Swallow capsules whole with a full glass of water. Dilute liquid in milk or fruit juice to mask the taste. Rectal microenema: insert the tip and squeeze the contents in fully.

Baseline. Cause of constipation; exclude obstruction. Review constipating medicines (opioids, anticholinergics, calcium-channel blockers, iron).

Monitoring.

• Stool frequency and consistency at 1 week.

• Fluid intake.

• Reassess the need to continue every 4 weeks.

Therapeutic drug monitoring. Not applicable.

Stopping. No taper is needed. Stop if no effect after 1 week and change to an osmotic or stimulant laxative.

Referral and escalation. Investigate constipation with red flags: weight loss, rectal bleeding, iron deficiency anaemia or change in bowel habit over age 50.