Generic Name

Mechanism of Action

Mechanism

Senna contains the anthraquinone glycosides sennosides A and B.
• Metabolic activation: In the colon, gut bacteria hydrolyze sennosides into active lactone metabolites (rhein anthrone).
• Stimulation of enteropooling: These metabolites increase intracellular Ca²⁺ in colonocytes, enhancing chloride and water secretion into the lumen.
• Smooth‑muscle agonism: The resulting osmotic load triggers peristaltic waves, promoting bowel evacuation.
• Short‑acting effect: Onset is 6–12 h; action ceases within 48 h after stopping.

Pharmacokinetics

• Absorption: Minimal systemic absorption; most sennosides remain in the gut.
• Distribution: Primarily confined to gastrointestinal tract; negligible plasma levels.
• Metabolism: Colonic bacterial hydrolysis → rhein anthrone (active metabolite).
• Elimination: Metabolites excreted in feces; renal clearance of unmetabolized sennosides < 3 %.
• Half‑life: Clinical effect lasts ~24–48 h; no significant systemic half‑life due to minimal absorption.

Indications

• Chronic constipation: Adults and pediatric patients >10 yrs with osmotic or stimulant laxative therapy.
• Pre‑operative bowel cleansing: As part of a bowel preparation regimen for colonoscopy or colorectal surgery.
• Temporary relief of fecal impaction (short course).

Contraindications

• Absolute contraindications
• Obstructive bowel disease (obstructive ileus, volvulus).
• Severe electrolyte depletion (hypokalemia 10 days):** Risk of colonic mucosal atrophy, electrolyte disturbances, and pseudo‑obstruction.
• Drug interactions: May reduce absorption of concurrent oral agents. Avoid simultaneous intake of calcium carbonate or magnesium-containing antacids.
• Adrenal insufficiency: Stimulation of colonic secretory activity can precipitate stress‑induced adrenal crisis in susceptible individuals.

Dosing

• Formulations: Oral tablets, capsules, and liquid solutions.
• Route: Oral only; avoid rectal administration.
• Compliance: Check for stool softening and patient comfort; advise a gradual taper for long‑term users.

Adverse Effects

• Common
• Abdominal cramping, bloating, increased stool frequency.
• Diarrhea (mild–moderate).
• Nausea, vomiting (rare).
• Serious
• Electrolyte imbalance: hypokalemia, hyponatremia.
• Dehydration, volume depletion.
• Colonic mucosal atrophy (chronic use).
• Pseudo‑obstruction (rare, usually with prolonged therapy).

Monitoring

• Baseline: Serum electrolytes (K⁺, Na⁺), hematocrit, fluid status.
• During therapy:
• Daily assessment of stool form (Bristol Stool Scale).
• Monitor for signs of dehydration (dry mucous membranes, reduced urine output).
• Repeat electrolytes if diarrhea persists >48 h.
• After prolonged use: Consider colonoscopy to rule out mucosal changes if therapy extended >10 days.

Clinical Pearls

• Timing matters – Administer senna after breakfast; fasting can reduce efficacy and increase GI upset.
• Hydration is key – Encourage adequate fluid intake to mitigate dehydration and preserve electrolyte balance.
• Use in synergy – Pair with bulk‑forming laxatives (e.g., psyllium) for synergistic stool softening, especially in chronic constipation.
• Avoid routine combo – Do not co‑administer with high‑dose calcium or potassium supplements; they may reduce efficacy and increase side‑effects.
• Short‑term only – Limit therapy to ≤ 10 days; longer courses warrant a careful risk‑benefit analysis and routine monitoring.
• Pediatric caution – Though effective in children over 10 yrs, use the lowest effective dose and watch for excessive cramping or dehydration.
• Pre‑op protocol – Include senna in a standard bowel prep protocol only when bowel cleansing is inadequate with diet and polyethylene glycol alone.

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• *All information is current as of 2026‑01‑02. Clinicians should consult local guidelines and the latest literature for updates.*