Drugs Affecting GI Tract Motility: Bulk-Forming and Stimulant Laxatives

Laxatives accelerate bowel movements, alleviating constipation. They increase intestinal water content, stimulate intestinal contractions, or lubricate fecal contents, facilitating fecal transit.

They are categorized based on their mechanism of action.

Bulk-forming laxatives, such as methylcellulose and psyllium husk, absorb water in the gut, forming a bulky mass that distends the colon and enhances bowel motility.

Stimulant laxatives, like senna, bisacodyl, and castor oil, function by irritating the intestinal lining. This causes an influx of water and electrolytes, initiating intestinal contraction for stool propulsion.

Senna is hydrolyzed in the colon, inducing bowel movement. Its adverse effects include nausea, vomiting, and abdominal pain.

Bisacodyl, activated by the intestinal esterases, stimulates colonic contractions. However, excessive use may cause severe mucosal inflammation and colonic ischemia.

Castor oil is hydrolyzed by intestinal lipases into glycerol and ricinoleic acid, which stimulates fluid secretion and promotes peristalsis.