Generic Name

Bisacodyl

Mechanism

Bisacodyl is a potent stimulant laxative. Its effectiveness stems from its lipophilicity, which permits rapid passage into the colon before it is metabolised. Once in the large intestine, it is converted by colonic bacteria into an active sulphate ester that:
• Stimulates enteric nerves – triggers peristaltic reflexes, increasing colonic motility.
• Directly depolarises smooth‑muscle cells – augments bowel contraction.
• Enhances fluid secretion – draws water and electrolytes into the lumen, softening stool.

The combined effect produces a bowel evacuation within 6–12 h, depending on formulation and oral‑absorptive characteristics.

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Pharmacokinetics

• Absorption: Little orally; most remains in the gut.
• Distribution: Minimal systemic distribution; its active sulphate metabolite is the pharmacologically relevant species.
• Metabolism: Prodrug → bisacodyl‑sulphate via colonic bacterial sulfatase.
• Elimination: Primarily fecal; <2 % renal excretion.
• Half‑life: 1–2 h for the active form; unchanged bisacodyl lasts longer in the bowel.
• Onset of action: 6–10 h (immediate‑release); 18–24 h for delayed‑release preparations.

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Indications

• Narrow‑spent constipation (adult and pediatric), particularly when quick resolution is desired.
• Pre‑operative bowel preparation for colonoscopy or abdominal surgery.
• Acute postoperative ileus (in controlled settings).
• Stool evacuation prior to flexible sigmoidoscopy.

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Contraindications

• Mechanical bowel obstruction, intestinal perforation, or severe ulceration – contraindicated.
• Known hypersensitivity to bisacodyl, phenolphthalein, or sulphate compounds.
• Severe electrolyte disturbances (hypomagnesaemia, hypokalaemia) – monitor closely.
• Renal insufficiency – reduced excretion may worsen electrolyte imbalance.
• Chronic use (>7 days) – risk of dependency and electrolyte depletion.
• Pregnancy & lactation: Use only when benefits outweigh potential risks; consult obstetrics and an obstetric‑gyn specialist.

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Dosing

Administration tips:
• Take with a full glass of water.
• Avoid coprescription with magnesium hydroxide or krep medications that may interfere.
• Delayed‑release tablets if patient can swallow; do not crush.

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Adverse Effects

Common:
• Abdominal cramping or discomfort
• Diarrhoea (flash)
• Nausea and vomiting (rare)
• Transient electrolyte shifts (Na⁺, K⁺, Mg²⁺)

Serious (less common):
• Severe electrolyte abnormalities (hyponatraemia, hypokalaemia).
• Colitis or back‑ache with prolonged use.
• Paradoxical constipation if over‑aerated.
• Bowel perforation (rare, often related to underlying diverticular disease).

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Monitoring

• Serum electrolytes (Na⁺, K⁺, Mg²⁺) in patients on chronic or high‑dose therapy.
• Stool frequency & consistency – target loose stool, 1–3 bowel movements/day.
• Signs of obstruction (abdominal distention, pain, vomiting).
• Weight loss in patients with chronic constipation therapy.

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Clinical Pearls

1. Delayed‑release bisacodyl offers a practical bridge between laxative potency and safety, yielding a rapid bowel emptying while limiting lower‑GI irritation that often accompanies immediate‑release formulations.

2. For pre‑operative bowel prep, the 20 mg delayed‑release dosing 36 h before colonoscopy achieves adequate catharsis in 70–80 % of patients, outperforming oral polyethylene glycol in patient‑reported tolerability.

3. Electrolyte monitoring is mandatory in any patient requiring >7 days’ bisacodyl, especially those with renal dysfunction or concurrent diuretic therapy.

4. Rectal bisacodyl 15 mg enema remains underutilised; it is particularly effective in patients unable to tolerate oral therapy or those with partial external obstruction.

5. Do not combine bisacodyl with other stimulant laxatives (e.g., senna, castor oil) without medical oversight—a practice that can precipitate paralytic ileus.

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• Key take‑away: Bisacodyl is an effective, rapid‑acting stimulant laxative for acute constipation and bowel prep, but diligent dosing, patient selection, and monitoring of electrolytes are critical to maximise benefit and minimise risk.