Stimulant Laxatives

Stimulant laxatives increase colonic motility through enteric nerve stimulation and reduce water absorption, and some also raise epithelial secretion. They act in 6 to 12 hours orally and within an hour rectally.

Classification. Diphenylmethanes (bisacodyl, sodium picosulfate) and anthraquinones (senna).

Pharmacokinetics. Bisacodyl and sodium picosulfate are converted by gut bacteria to active metabolites. Senna glycosides are activated in the colon.

• Bisacodyl 5 to 10 mg orally at night; 10 mg suppository in the morning.
• Senna 7.5 to 15 mg orally at night.
• Sodium picosulfate 5 to 10 mg orally at night; higher doses with magnesium citrate in bowel preparation.
• Glycerol suppository, a mild rectal stimulant.

Differences. Suppositories give predictable timing. Senna may colour urine yellow brown.

• Constipation not controlled by bulk or osmotic agents.
• Opioid-induced constipation, combined with an osmotic agent.
• Bowel preparation before colonoscopy or surgery.
• Faecal loading with a distal impaction.

Selection. Intermittent use in non-opioid constipation; regular use is acceptable in people on opioids.

Contraindications. Intestinal obstruction, acute abdomen, acute inflammatory bowel disease, toxic megacolon, severe dehydration.

Adverse effects. Cramps, diarrhoea, hypokalaemia, dehydration, anal irritation (suppositories). Melanosis coli is benign. Long-term use does not cause a proven cathartic colon.

Interactions. Hypokalaemia increases digoxin toxicity and QT risk with other drugs. Combine with diuretics or corticosteroids with care.

Special groups.

• Pregnancy: senna and bisacodyl acceptable for short courses.
• Breastfeeding: acceptable; infant diarrhoea is rare.
• Children: use product-specific doses.
• Older adults: monitor fluids and potassium.
• Kidney impairment: no adjustment; watch electrolytes.

Monitoring. Potassium, hydration and stool frequency with regular use.

Referral and escalation. Severe abdominal pain, vomiting or distension, rectal bleeding, or laxative dependence with suspected abuse.