Constipation

There are three main types of laxatives. One consists of the so-called stimulant or irritant laxatives, which promote mass peristalsis. These include cascara, senna, bisacodyl, phenolpthalein, docusate, and picosulphate. The second group promote an outpouring of fluid from the bowel washing out the fecal mass; these are generally known as osmotic laxatives. They include magnesium sulfate, magnesium hydroxide, and lactulose (whose main ingredient is a semisynthetic disaccharide). Either of these types may cause colic or fecal incontinence.

The third type—bulk laxatives—include substances that swell when mixed with water. They include ispaghula, sterculia, methyl cellulose, and bran. They are generally available in powder form and taken in water, and may need to be taken for a few days before becoming effective.

Other miscellaneous laxatives include mineral oil and docusate sodium. The former should be avoided in elderly people because of its possible side effects, which include anal leakage, absorption of fat-soluble vitamins (especially vitamin D, which if long continued may diminish bone density (see osteo malacra), and inhalation pneumonia. Docusate sodium, which is really a stool softener, is useful to prevent the accumulation of hard fecal masses.

Finally, suppositories or enemas may be used, particularly where a fairly speedy result is desired, though few people have difficulty in retaining them. Suppositories may increase bulk in the rectum by their hygroscopic, or osmotic, effect (e.g., glycerin), or they may stimulate mass peristalsis (e.g., bisacodyl). Prepacked enemas generally contain hypertonic phosphates which have a hygroscopic effect.