Q: What treatments are available? How do they act and what, if any, drawbacks do they have?

A:

Bulk-forming laxatives – ispaghula husk, sterculia, methylcellulose

• Increase faecal volume by adding directly to the volume of intestinal contents, softening faeces and adding to faecal mass by acting as substrates for the growth of colonic bacteria.
• Provide the closest approximation to the natural process of increasing faecal volume and are normally the first-line recommendation for functional constipation. 
• Not absorbed, so no systemic effects. Do not interact with other medicines or interfere significantly with drug absorption. 
• Adverse effects and disadvantages include: risk of oesophageal and intestinal obstruction if preparations are not taken with sufficient water; abdominal distension; flatulence.

Stimulant laxatives – senna, bisacodyl, glycerol suppositories, docusate sodium

• Act mainly by stimulating the intestinal mucosa to secrete water and electrolytes. They may also cause direct damage to mucosal cells, increasing their permeability and allowing fluid to leak out, thus increasing fluid volume in the intestine.

• Length of time for individual stimulant laxatives to take effect varies from four to 12 hours, depending on their site of action within the intestine. Doses are usually taken at bedtime to produce an effect the next morning. Suppositories usually produce results within an hour.

• Docusate is a faecal softener as well as a stimulant laxative.

• Main adverse effects are griping and intestinal cramps; prolonged use may produce colonic atony and permanent constipation.

Osmotic laxatives – lactulose, macrogols, magnesium hydroxide, magnesium sulfate

• Inorganic or organic compounds that are poorly absorbed, creating a hypertonic state in the intestine. To equalise osmotic pressure, water is drawn from the intestinal wall into the lumen, increasing the volume of the contents, stimulating peristalsis and promoting evacuation.
• Inorganic salts provide more rapid results, but large doses may cause nausea and vomiting.
• Lactulose, a synthetic disaccharide, takes up to 72 hours of regular dosing to produce an effect. Its intensely sweet taste and large dose volumes may be a deterrent to compliance.
• Macrogols (polyethylene glycols) tend to act faster than lactulose. 
• Serious adverse effects are rare; minor side-effects include flatulence, cramp and abdominal discomfort.