Mechanism of Action
Bisacodyl (Bisacodylum) belongs to the class of contact (stimulant) laxatives and is a synthetic diphenylmethane derivative.
Its mechanism is resorptive in nature. After oral administration, the drug is absorbed in the small intestine and then secreted back into the lumen of the large intestine. Additionally, the drug is hydrolyzed in the alkaline environment of the bowel. This produces active metabolites that directly irritate the mucosal chemoreceptors, leading to a reflex enhancement of peristalsis.
It is important to emphasize that bisacodyl acts exclusively in the large intestine. This fundamentally differentiates it from saline laxatives (such as magnesium sulfate or sodium sulfate), which act throughout the entire gastrointestinal tract. It also differs from osmotic agents and bulk-forming laxatives (such as kelp or methylcellulose) because it does not work by increasing stool volume or providing lubrication (like mineral oils).
Pharmacological Effects
The primary pharmacological effect is laxative. Its potency is considered moderate (less pronounced than that of saline laxatives).
- When taken orally (per os), the effect develops in 5–7 hours.
- When administered rectally (as suppositories), the action is significantly faster—within 1 hour.
Classification and Comparison with Analogues
In laxative classifications, bisacodyl is categorized as a synthetic stimulant acting on chemoreceptors. Other agents in this subgroup include phenolphthalein, oxyphenisatin, and sodium picosulfate.
- Phenolphthalein is considered the reference standard of the group; however, long-term use carries a risk of bioaccumulation and potential nephrotoxicity.
- Oxyphenisatin is an analogue of phenolphthalein but exhibits lower toxicity.
- Sodium picosulfate, unlike bisacodyl, is not absorbed in the small intestine at all and is hydrolyzed by colonic bacterial flora to release the active free diphenol.
Bisacodyl should also be distinguished from plant-based laxatives containing anthraquinone glycosides and oils (senna, rhubarb root, buckthorn bark, castor oil) and from disaccharides (lactulose).
Indications for Use
In clinical practice, the drug is prescribed for:
- Treatment of constipation of various etiologies (to facilitate bowel evacuation).
- Preoperative preparation (for adequate bowel cleansing prior to surgical procedures).
- Food poisoning (as part of combination therapy to accelerate the removal of toxins from the gastrointestinal tract).
Administration and Prescription Writing
The drug is available in two dosage forms: 5 mg tablets and 10–20 mg rectal suppositories.
Oral administration: Taken 30 minutes before breakfast. Tablets must be swallowed whole without chewing to ensure the drug reaches the alkaline environment of the intestine. The single dose is 1–2 tablets. The maximum single dose is 25 mg, and the maximum daily dose is 50 mg.
Rectal administration: 1–2 suppositories rectally per day.
Example prescription for tablets: ```latin Rp.: Tab. Bisacodyli 0.005 D.t.d. N. 30 S. Take 1-2 tablets orally 30 minutes before breakfast, without chewing. ```
Example prescription for suppositories: ```latin Rp.: Supp. cum Bisacodylo 0.01 D.t.d. N. 10 S. Insert 1 suppository rectally once daily. ```