Proprietary laxatives represent a multimillion dollar industry and are widely used by the apparently well population. They are traditionally classified into bulk laxatives, lubricants, stimulants, stool softeners, and osmotic laxatives. The latter 3 probably act mainly by favouring accumulation of fluids and electrolytes in the lumen of the gut. Magnesium-containing saline laxatives are believed to act by releasing cholecystokinin which, in turn, favours intraluminal fluid accumulation. Bran is not a proprietary laxative. It is a bulking agent with capacity to hold water in the stool, thereby improving bowel function. The lubricant, mineral oil (liquid paraffin), is obsolete.
In constipation associated with the spastic colon, bran will transform the difficult-to-pass scybala into softer, bulkier and more easily passed stools. Atonic constipation, in which defaecation fails to be triggered by a full rectum, is less satisfactorily treated with bran. In these individuals, chronic laxative use often compounds the problem. Bowel retraining with occasional (and decreasing) use of laxatives such as bisacodyl or ‘Senokot’ (standardised senna) are often effective. Occasionally, a glycerin suppository will trigger the defaecation reflex.
Patients with an acute illness, undergoing surgery or suffering from perianal disease benefit from the early institution of bran to encourage the easy passage of soft stool. Bisacodyl or ‘Senokot’ should be kept in reserve. In patients who become impacted, particularly following a barium enema, an oil retention enema followed by a tap water enema may be successful, but manual disimpaction should not be unduly delayed. Laxatives may alter the appearance of the colon mucosa and so should be avoided before sigmoidoscopy. Preparation for an air contrast barium enema or colonoscopy necessitates a 2 day program of taxation including a fluid diet.
Laxatives are probably more important to modern medicine for the harm they do than for their benefit. Use of the stimulant cathartics can lead to an atonic colon in which the neuromuscular apparatus is permanently damaged. Vigorous purgation may produce a paradoxical diarrhoea complicated by electrolyte derangement, malabsorption, and protein-losing enteropathy. Other than bran, most clinicians will have little need for laxatives and their use by patients should also be discouraged.
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Thompson, W.G. Laxatives: Clinical Pharmacology and Rational Use. Drugs 19, 49–58 (1980). https://doi.org/10.2165/00003495-198019010-00004
- Ricinoleic Acid
- Stimulant Laxative