Bisacodyl

BRAND NAMES

Common brand names include:

• Dulcolax (most well-known globally).

• Correctol.

• Fleet Bisacodyl.

• Carter’s Little Pills.

• Alophen.

• Feen-a-Mint.

• Modane.

Oral tablets: Typically work within 6–12 hours.

Rectal suppositories: Act faster, usually within 15 minutes to 1 hour.

MECHANISM OF ACTION

Bisacodyl is a stimulant laxative that works by a dual mechanism of action on the colon, increasing both motility and fluid secretion. As an oral prodrug, it is activated in the colon by enzymes to form its active metabolite, bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM). BHPM then stimulates the enteric neurons, promoting propulsive contractions, and directly irritates the intestinal muscle, leading to increased peristalsis. Simultaneously, it increases the accumulation of water and electrolytes in the intestinal lumen while inhibiting their absorption, which softens the stool and facilitates a bowel movement.

PHARMACOKINETICS

Absorption

Bisacodyl is minimally absorbed from the gastrointestinal tract and acts primarily as a local stimulant. The laxative effect is caused by the active metabolite, bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM), which is produced in the colon. The BHPM directly irritates the lining of the intestines, which stimulates muscle contractions and increases fluid and electrolyte secretion. This local effect prompts a bowel movement, and because systemic absorption is low, its therapeutic action is confined to the colon.

Distribution

Bisacodyl is a locally acting laxative that is minimally absorbed and primarily distributed to the large intestine. The drug is formulated to resist breakdown in the stomach and small intestine, allowing it to reach the colon where it is converted into its active metabolite. 

Metabolism

Bisacodyl undergoes metabolism primarily in the large intestine, where it is converted into its active form, bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM). This transformation is crucial for its stimulant laxative effect, which acts locally in the colon. Only a small portion of bisacodyl is absorbed into the bloodstream, where it is further processed in the intestinal wall and liver into inactive BHPM glucuronide. Most of the drug and its metabolites are eliminated through the feces, with only trace amounts excreted in the urine.

Excretion

The primary route of bisacodyl elimination is through the feces, while approximately 13% to 17% of the administered dose is excreted in the urine as the active metabolite.

PHARMACODYNAMICS

Bisacodyl’s pharmacodynamics involve its conversion into the active metabolite BHPM within the colon. BHPM stimulates the enteric nerves and the colonic mucosa, enhancing colonic motility and increasing fluid secretion. This dual action prokinetic (boosting movement) and secretory (promoting fluid release) helps reduce intestinal transit time and soften the stool, ultimately facilitating defecation.

DOSAGE AND STRENGTHS

1. Oral Tablets (Enteric-Coated)

• Strengths: 5 mg per tablet.

• Typical Adult Dose: 5 to 15 mg once daily, start with 5 mg; increase to 10–15 mg if needed

2. Rectal Suppositories:

• Strengths: 10 mg (adult), 5 mg (pediatric)

• Typical Adult Dose: 10 mg once daily (usually produces results within 15 to 60 minutes)

3. Rectal Enema:

• Strength: Varies (usually contains 10 mg bisacodyl per dose)

• Do not crush or chew oral tablets (they are enteric-coated).

DRUG INTERACTIONS

Oral bisacodyl should not be taken within one hour of dairy products or antacids, as these can dissolve the tablet's protective coating prematurely and cause stomach irritation or reduce its effectiveness. Combining bisacodyl with other laxatives, diuretics, or corticosteroids increases the risk of dehydration and electrolyte imbalances. Patients taking heart medications, such as digoxin, should be especially cautious, as bisacodyl's effect on electrolytes can increase the risk of serious side effects. Chronic or excessive use of any laxative, including bisacodyl, can lead to dependence.

FOOD INTERACTIONS

The most important food interaction to be aware of when taking oral bisacodyl is with dairy products. Bisacodyl tablets have an enteric coating designed to prevent them from dissolving prematurely in the stomach, which can cause irritation and cramping. Dairy products like milk, cheese, and yogurt can compromise this protective coating, causing the tablet to dissolve too early. This can result in increased stomach upset, cramps, or a less effective medication. To avoid this interaction, you should not take bisacodyl tablets within one hour of consuming any dairy products.

CONTRAINDICATIONS

• Gastrointestinal conditions

• Intestinal blockage or ileus.

• Severe fecal impaction.

• Acute surgical abdomen conditions, such as appendicitis.

• Severe, persistent abdominal pain with nausea or vomiting.

• Acute inflammatory bowel diseases, such as ulcerative colitis or Crohn's disease.

• Undiagnosed rectal bleeding.

• Anal fissures or ulcerative proctitis.

SIDE EFFECTS

Common side effects:

• Abdominal cramps and pain.

• Diarrhea.

• Nausea and vomiting.

• Dizziness or faintness.

• Rectal burning.

• Bloating and gas.

Serious side effects:

• Rectal bleeding or no bowel movement.

• Severe allergic reaction.

• Signs of dehydration or electrolyte imbalance.

• Fluid and electrolyte disturbances.

OVERDOSE

• Severe diarrhea.

• Abdominal cramps or pain.

• Dehydration.

• Electrolyte imbalances (hypokalemia).

• Dizziness or weakness.

• Nausea and vomiting.

In extreme or prolonged cases:

• Kidney dysfunction.

• Muscle spasms or irregular heartbeat (due to electrolyte loss).

• Chronic laxative dependence.

TOXICITY

Bisacodyl toxicity results from overdose or chronic abuse, leading to severe dehydration and dangerous electrolyte imbalances. Symptoms can range from mild gastrointestinal distress to serious and potentially life-threatening cardiac or neurological issues.