Makindo Medical Notes

🌿 Senna is a stimulant laxative derived from the leaves and pods of the Cassia senna plant. It promotes colonic motility and stool evacuation, typically acting within 6–12 hours. Best taken at night for a morning bowel movement.

🧠 About

• Contains sennosides A and B, which are anthraquinone glycosides.
• Activated by colonic bacteria into rhein anthrone, the compound responsible for its stimulant effects.
• Commonly combined with a softening agent (e.g. docusate) for postoperative or opioid-related constipation.
• Widely used in hospitals for bowel regulation — especially in the elderly, immobile, or opioid-treated patients.
• Typical onset of action: 6–12 hours.

⚙️ Mode of Action

• Stimulates colonic peristalsis by directly irritating the mucosal nerve plexus (Auerbach’s and Meissner’s plexuses).
• Increases water and electrolyte secretion into the intestinal lumen.
• Reduces colonic water reabsorption, producing softer, looser stools.
• Unlike bulk-forming laxatives, senna acts primarily on smooth muscle rather than stool volume.

🎯 Indications

• Short-term treatment of constipation.
• Opioid-induced constipation (with docusate or macrogol).
• Pre-procedural bowel evacuation (e.g. before colonoscopy or surgery).
• Occasionally used for postoperative bowel stimulation following abdominal surgery (after excluding obstruction).

💊 Dose

• Tablets: Senna 15–30 mg (usually 2–4 tablets) taken at night for effect the next morning.
• Oral liquid: 10–20 mL once daily at night, titrated to effect.
• Adjust dose to produce one soft bowel movement daily; reduce once regularity is established.

⚠️ Cautions

• Ensure adequate hydration and mobility — dehydration increases cramping risk.
• Chronic use (>1 week) may lead to hypokalaemia or atonic colon (“lazy bowel”).
• Prolonged or excessive use may cause melanosis coli (harmless pigmentation of colonic mucosa).
• Use cautiously in frail or malnourished patients prone to electrolyte disturbances.

🚫 Contraindications

• Intestinal obstruction or ileus.
• Undiagnosed abdominal pain (rule out obstruction or appendicitis first).
• Severe inflammatory bowel disease or acute surgical abdomen.

💊 Adverse Effects

• Common: abdominal cramps, urgency, diarrhoea.
• Occasional: electrolyte loss (especially potassium), weakness, nausea.
• Rare: hepatotoxicity or pseudomelanosis coli with long-term use (benign and reversible).

🤰 Pregnancy & Lactation

• Considered safe for short-term use in pregnancy — little systemic absorption.
• Preferred stimulant if osmotic agents (e.g. lactulose) ineffective.
• Compatible with breastfeeding; minimal transfer into breast milk.

🩺 Practical Prescribing Notes

• Combine with stool-softeners (e.g. docusate sodium) for opioid-related constipation.
• If ineffective, switch to or add an osmotic laxative (e.g. macrogol).
• For frail older adults: use the lowest effective dose and review every few days.
• Reinforce dietary fibre, hydration, and mobilisation.

💡 Teaching Tip

• Senna demonstrates the neuro-secretory mechanism of bowel stimulation — unlike osmotics that act via water retention.
• Good for contrasting with bulk-formers (e.g. ispaghula) and osmotics (e.g. lactulose).
• Explain to learners: “Senna irritates; lactulose lubricates; ispaghula bulks.”

📚 References

• BNF: Senna
• NICE CKS: Constipation in adults (2024)
• Camilleri M. NEJM 2021;385:488–498 — Mechanisms and management of chronic constipation.