1. Clinical Overview
Bisacodyl is a stimulant laxative belonging to the diphenylmethane derivative class. It is a prodrug that is hydrolyzed by intestinal enzymes to its active metabolite, bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM), which directly stimulates the colonic myenteric plexus, leading to increased peristalsis and fluid accumulation in the colon. It is a first-line agent for the treatment of occasional constipation and is widely used for bowel preparation prior to diagnostic procedures like colonoscopy.
| Onset | Duration | Bioavailability |
|---|---|---|
| Oral: 6 to 12 hours. Rectal: 15 to 60 minutes. | Approximately 12 to 24 hours. | Oral: Approximately 5% (due to extensive first-pass metabolism). Rectal: Variable, but systemic absorption is minimal. |
2. Mechanism of Action
Bisacodyl is a prodrug that is converted by intestinal sulfatases and esterases to its active metabolite, BHPM. This metabolite directly stimulates the sensory nerve endings (submucosal plexus) in the colonic mucosa, which triggers the release of prostaglandins and nitric oxide. This leads to: 1) Increased secretion of water and electrolytes into the colonic lumen by inhibiting Na+/K+ ATPase and stimulating chloride channels. 2) Enhanced colonic motility and powerful peristaltic contractions (colonic giant migrating contractions) by stimulating the myenteric plexus.
3. Indications & Uses
- Treatment of occasional constipation
- Bowel evacuation prior to surgical or diagnostic procedures (e.g., colonoscopy, radiology)
- Management of opioid-induced constipation (when other measures fail)
4. Dosage & Administration
Adult Dosage: Oral: 5mg to 10mg (1-2 tablets) once daily, preferably at bedtime. Rectal Suppository: 10mg (one suppository) once daily.
Administration: Oral Tablet: Swallow whole with a full glass of water. Do NOT crush, chew, or break the enteric coating. Take at bedtime for morning evacuation. Do not take within 1 hour of antacids, milk, or proton pump inhibitors (PPIs). Rectal Suppository: Insert suppository high into the rectum. Retain for 15-20 minutes. Use only when a bowel movement is desired within 1 hour.
5. Side Effects
Common side effects may include:
- Abdominal discomfort/cramping
- Nausea
- Flatulence
- Perianal irritation (with suppository)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Antacids, H2 Blockers, PPIs (e.g., Omeprazole) | Premature dissolution of enteric coating leading to gastric irritation and reduced efficacy. | Major |
| Diuretics (e.g., Furosemide) or Corticosteroids | Increased risk of hypokalemia due to additive potassium-wasting effects. | Moderate |
| Digoxin | Hypokalemia potentiates the risk of digitalis toxicity (arrhythmias). | Major |
| Antiarrhythmics (e.g., Amiodarone, Quinidine) | Electrolyte disturbances can alter cardiac conduction. | Moderate |
| Oral Medications (especially enteric-coated) | Bisacodyl-induced rapid intestinal transit may reduce absorption of other drugs. | Moderate |
| Opioid Analgesics (e.g., Morphine) | Therapeutic interaction: Used to treat opioid-induced constipation. Pharmacodynamic antagonism. | Therapeutic |
7. Patient Counselling
- DO swallow the tablet whole with a full glass of water.
- DO take it at bedtime for a bowel movement in the morning.
- DO NOT crush, chew, or break the tablet.
- DO NOT take it within 1 hour of consuming milk, antacids, or stomach acid reducers.
- DO NOT use for more than 7 days unless directed by a doctor.
- DO NOT use if you have severe stomach pain, nausea, or vomiting.
- DO increase dietary fiber and fluid intake as a long-term strategy for constipation.
8. Toxicology & Storage
Overdose: Severe cramping abdominal pain, profuse watery diarrhea leading to dehydration and hypovolemic shock, electrolyte depletion (hypokalemia, hyponatremia), weakness, cardiac arrhythmias, and renal failure.
Storage: Store below 30°C, in a cool, dry place. Protect from moisture and light. Keep out of reach of children. For suppositories, store in a refrigerator (2°C to 8°C).