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

Laxatives enhance bowel movements and alleviate constipation. They augment the stool's bulk, stimulate intestinal muscle contractions, draw water into the intestines, or soften the stool. There are five key types of laxatives: bulk laxatives, stimulant laxatives, osmotic laxatives, stool softeners, and lubricant laxatives.

Bulk-forming laxatives, such as psyllium, methylcellulose, and polycarbophil, absorb water in the intestine, increasing stool bulk and promoting bowel movement. This makes them particularly beneficial for managing chronic constipation and conditions like irritable bowel syndrome (IBS).

On the other hand, stimulant laxatives irritate the intestinal lining, triggering muscle contractions that propel the stool forward. They provide short-term relief from constipation and are beneficial when different laxative types prove ineffective. Typical examples of stimulant laxatives include Senna, an anthraquinone glycoside derivative; bisacodyl (Dulcolax), a diphenylmethane derivative; and castor oil, a source of ricinoleic acid. Senna, which is derived from plants such as Cassia acutifolia or Cassia angustifolia, increases water and electrolyte secretions and may cause abdominal cramping, nausea, and diarrhea as side effects. Bisacodyl is available as enteric-coated tablets and suppositories. Its prolonged use results in mucosal inflammation and colonic ischemia. Castor oil should be avoided by pregnant women, as it stimulates uterine contractions.