Laxatives (purgatives or cathartics) promote defaecation and are used in the treatment of constipation (see below) and for bowel evacuation before investigational procedures, such as endoscopy or radiological examination, or before surgery.
Laxatives are frequently used for self-medication. Abuse of laxatives is a well-known phenomenon mat may occasionally lead to toxicity.
Laxatives may be classified according to their mode of action. There is, however, a degree of overlap between the various groups and in some cases the precise mechanisms of action are not fully understood. Many traditionally used laxatives have fallen from use owing to the violence of their action or their adverse effect profile.
• Bulk laxatives (bulk-forming laxatives or bulking agents) cause retention of fluid and an increase in faecal mass resulting in stimulation of peristalsis. Owing to their hydrophilic nature, bulk laxatives may also be used to control diarrhoea and to regulate the consistency of effluent in colostomy patients. Those described in this site include bran, ispaghula, and sterculia.
• Stimulant laxatives (contact laxatives) act by directly stimulating nerve endings in the colonic mucosa, thereby increasing intestinal motility. It is mis group of laxatives which is most commonly associated with abuse. Those described in mis site include bisacodyl, cascara, phenolphthalein, senna, and sodium picosulfate.
• Osmotic laxatives act by increasing intestinal osmotic pressure thereby promoting retention of fluid within the bowel. Those described in mis site include saline laxatives such as magnesium citrate, magnesium hydroxide, and sodium sulfate (for magnesium sulfate and sodium phosphate). Lactulose may also be classified as an osmotic laxative because its breakdown products exert a similar effect. Also included in mis group are the hyperosmotic laxatives such as glycerol and sorbitol, and the macrogols.
• Faecal softeners (emollient laxatives) are claimed to act by decreasing surface tension and increasing penetration of intestinal fluid into the faecal mass. Those described in mis site include docusate (which is also believed to have a stimulant action).
For the lubricant laxative liquid paraffin see site.
Described in this site are:
Potassium Acid Tartrate
Potassium Sodium Tartrate