cathartic /kəthär″tik/ [Gk, cleansing] , 1. adj., pertaining to a substance that causes evacuation of the bowel. 2. n., an agent that promotes bowel evacuation by stimulating peristalsis, increasing the fluidity or bulk of intestinal contents, softening the feces, or lubricating the intestinal wall. The term cathartic implies a fluid evacuation, in contrast to laxative, which implies the elimination of a soft, formed stool. Cathartics that increase peristalsis, usually by irritating intestinal mucosa, include certain plant substances, such as aloe, colocynth, croton oil, podophyllum senna, phenolphthalein, bisacodyl, and dehydrocholic acid. Saline cathartics, such as sodium sulfate, magnesium sulfate, and magnesium hydroxide, dilute the intestinal contents by retaining water through osmotic forces. Suppositories containing sodium biphosphate, sodium acid pyrophosphate, and sodium bicarbonate induce defecation when the salts react to form carbon dioxide and the expanding gas stimulates peristalsis. Also called coprogogue. −catharsis, n.
