Miralax (Bisacodyl) is a Stimulant Laxative
Bisacodyl (Miralax) belongs to the stimulant laxative class of medications, specifically the diphenylmethane derivatives family. 1, 2 This classification is based on its mechanism of action, which involves stimulating intestinal motility and increasing water content in the stool.
Mechanism of Action
Bisacodyl works through a dual mechanism:
- Prokinetic effect: Stimulates intestinal motility by acting on the colonic mucosa
- Secretory effect: Increases water content in the stool
Specifically, bisacodyl:
- Must be converted to its active metabolite bis-(p-hydroxyphenyl)-pyridyl-2-methane (BHPM) in the gut 3
- Acts locally in the large bowel 3
- Stimulates sensory nerves in the proximal colon 1
- Increases sodium and water movement into the colonic lumen 1
Classification Context
Stimulant laxatives are one of several categories of laxatives:
- Bulk-forming laxatives: Methylcellulose, ispaghula, sterculia
- Osmotic laxatives: Macrogols (polyethylene glycol), lactulose, magnesium salts
- Stimulant laxatives:
- Anthraquinones: Senna, cascara
- Diphenylmethane derivatives: Bisacodyl, sodium picosulfate, phenolphthalein
- Stool softeners: Docusate sodium
- Lubricants: Liquid paraffin
Clinical Efficacy
Bisacodyl has demonstrated effectiveness in treating constipation:
- Doubles the mean number of bowel movements per week compared to baseline 4, 5
- Shows similar efficacy to newer agents like prucalopride and linaclotide for achieving complete spontaneous bowel movements 3
- May be superior to other laxatives for increasing spontaneous bowel movements per week 3
Important Considerations
- Duration of use: While effective for short-term use, evidence for long-term use beyond 4 weeks is limited 6
- Side effects: Generally mild but common (up to 72%), including diarrhea and abdominal pain 6
- Contraindications: Should be avoided in intestinal obstruction 1
- Excessive use: Can cause diarrhea and hypokalemia 1
Clinical Application
Bisacodyl is typically used:
- When osmotic laxatives provide inadequate response 1
- At a standard dose of 5-10 mg daily 4, 5
- As a fast-acting stimulant laxative 2
It's important to note that despite concerns about long-term use of stimulant laxatives potentially damaging intestinal muscle or neurons, there is no clinical or animal evidence supporting this theory 1.