16.03.2 Treatment for Constipation

The first treatment for constipation is lifestyle changes such as having a diet rich in fibre, decreasing the dietary fat intake, and increasing the intake of fluids but these fluids should not be diuretics as they promote water loss from the body. Daily exercise also stimulates peristalsis to overcome constipation.

In terms of agents used to overcome constipation, the old remedy of castor oil is effective but unpleasant, and potentially toxic, and therefore rarely used these days. Alternatives include bulk-forming laxatives, faecal softening agents, irritant laxatives and osmotic laxatives.

Dietary fibre is resistant to enzymatic degradation and presented to colon unchanged, and thus increasing bulk stimulates peristalsis. Bulk-forming laxatives mimic this effect. Methylcellulose (sold as Citrucel) is poorly fermented. Poorly fermented fibre attracts water to increase stool bulk, which stimulates peristalsis and eases movement along the gastrointestinal tract. Bulk-forming laxatives are commonly used to prevent constipation in subjects prone to constipation.

Another example of a bulk-forming laxative is the commonly used psyllium husk. Psyllium husk is derived from the plantago seed and is in many commercial products for constipation (as Metamucil). It is fermented by the colonic bacteria to increase the bulk in the colon, and stimulate peristalsis. The fermentation also produces short chain fatty acids, which stimulate motility in the gastrointestinal tract (are prokinetic).

The faecal softening agents include docusate and liquid paraffin. Docusate acts like a detergent to allow water and fatty substances to mix with faecal material to soften it, and make it easier to pass stools. After the oral administration of docusate, there is an excretion of stools in 1-3 days. For a faster excretion, rectal administration of docusate can be used, and gives excretion of stools in 15 minutes.

Liquid paraffin is not dangerous after oral administration, as the absorption is minimal. The liquid paraffin stays in the tract, and coats stools to prevent loss of water. The major problem with using liquid paraffin as a faecal softening agent is that it can prevent the absorption of fat soluble vitamins (A, D, E and K), which will dissolve in the liquid paraffin and be excreted.

Agents that stimulate or irritate the colon to cause contraction include bisacodyl and senna. By stimulating colon contractions, bisacodyl and senna cause bowel evacuation in 6 to 12 hours. The faecal-softening agents and irritant laxatives are used in constipation.

The osmotic laxatives are poorly absorbed, and draw water toward them by osmosis. Subsequently, the osmotically-mediated water retention stimulates peristalsis. Examples of osmotic laxatives include glycerol, certain salts, and lactulose. Glycerol is an osmotic laxative, which is used rectally. After rectal administration, glycerol stimulates a bowel movement in an hour. Glycerol is used in constipation and constipation associated with irritable bowel syndrome.

The salts include milk of magnesia and Epsom salts. Lactulose is a non-digestible carbohydrate. Both salts and lactulose are taken orally, and in a low dose are laxative, but at high dose are cathartic (uncontrollable stools). As laxatives, the salts work in 6 to 8 hours, lactulose takes longer, 24 to 48 hours.