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Definition: laxative from Philip's Encyclopedia

Any agent used to counteract constipation. There are various kinds available, including bulk-forming drugs, stimulant laxatives, fecal softeners, and saline purgatives.


Summary Article: Laxatives
from Black's Medical Dictionary, 43rd Edition

Drugs or other substances used to treat CONSTIPATION. Also called aperients or purgatives, laxatives are classified according to their mode of action. The four main groups are bulk, stimulant, faecal softeners and osmotics. In addition, bowel-cleansing solutions are used before surgery, ENDOSCOPY, or radiological examination of the COLON, to ensure that the bowel is clear of solid matter. However, these are not procedures for treating constipation.

Normal bowel habits vary greatly, from twice a day to once every two or even three days. Any change from normal frequency to irregular or infrequent defaecation may signal constipation. Furthermore, before laxatives are prescribed, it is essential to ensure that the constipation is not the result of an underlying condition producing ‘secondary’ constipation. Individuals should not use laxatives too often or indiscriminately; persistent constipation is a reason to seek medical advice.

Bulk

laxatives include bran and most high-fibre foods, such as fruit, vegetables and wholemeal foods. These leave a large indigestible residue that retains water in the gut and produces a large soft stool. Ispaghula husk, methyl cellulose and stercula are helpful when bran is ineffective. Inorganic salts such as magnesium sulphate (Epsom Salts) have a similar effect.

Stimulant

laxatives – for example, bisacodyl, senna and docusate sodium – stimulate PERISTALSIS, although this action may be accompanied by colicky pains.

Faecal softeners (emollients)

There are two groups: surface active agents such as dioctyl sodium sulphosuccinate, which retains water in the stools and is often combined with a stimulant purgative; and liquid paraffin, which is chemically inert and said to act by lubrication.

Osmotic laxatives

These substances act by holding fluid in the bowel by OSMOSIS, or by altering the manner in which water is distributed in the FAECES. Lactulose, macrogols and magnesium salts are used to produce rapid bowel evacuation. Phosphate or sodium citrate enemas (see ENEMA) can be used for constipation, while the former is used to ensure bowel evacuation before abdominal radiological procedures, endoscopy and surgery.

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