Stimulant laxatives are believed to produce laxation by directly stimulating peristaltic movement of the intestine via local mucosal irritation, thus increasing motility. More recent studies suggest that bisacodyl promotes evacuation of the colon by altering intestinal fluid and electrolyte absorption. This causes a net intestinal fluid accumulation and produces laxation. Bisacodyl distributes locally, and the circulating drug undergoes hepatic metabolism and is then excreted in the urine. Stimulant laxatives, such as bisacodyl, are the laxatives most likely to cause GI irritation, fluid and electrolyte loss, nausea, vomiting, or diarrhea.
Laxative dependence can occur with long-term or excessive laxative therapy.
Bisacodyl administration can exacerbate ulcerative colitis, rectal fissures, ulcerative lesions of the colon, and fecal impaction. Therefore, the drug is contraindicated in patients with these conditions. Prolonged bisacodyl therapy can cause potassium depletion. If multiple enemas are required, bisacodyl tannex should not be used because of the risk of increased absorption of tannic acid, leading to hepatotoxicity and possibly death. Recommended dosages of bisacodyl tannex should not be exceeded.