• Bulk-forming laxatives: Act by retaining fluid within the stool and increasing faecal mass, leading to stimulation of peristalsis. Also have stool-softening properties. Useful first-line choice in adults when it is difficult to get enough fibre in the diet. Better tolerated than bran. Must not be taken immediately before bed. Adequate fluid intake is important, to prevent intestinal obstruction - may be difficult for the frail or children. Ispaghula (also known as psyllium), methylcellulose, wheat or bran

• Osmotic laxatives: Act by retaining fluid in the bowel, and drawing fluid from the body into the bowel producing distension, leading to stimulation of peristalsis. Lactulose and macrogols (polyethylene glycol (Movicol)) also have stool-softening properties. Lactulose: some find it sickly sweet (1M-1Y: 2.5ml BD; 1-5Y: 2.5-10ml BD; 5-18Y: 5-20ml BD). Movicol paediatric: not licensed for chronic constipation in children aged <2Y (<1Y: half to 1 sachet daily; 1-6Y: 1 sachet daily (max 4); 6-12Y: 2 sachets daily (max 4)). Movicol: chronic constipation age 12-18Y: 1-3 sachets daily (mix in half glass water). Impaction: aged 12-18: see BNF. Movicol-Half contains half the dose and electrolytes

• Surface-wetting laxatives: Reduce the surface tension of the stool, allowing water to penetrate and soften it. Docusate also has a relatively weak stimulant effect. Docusate sodium: May be a useful alternative for people who find it hard to increase their fluid intake

• Stimulant laxatives: Cause peristalsis by stimulating colonic nerves (senna) or colonic and rectal nerves (bisacodyl, sodium picosulfate). Senna: Licensed only for short-term use. Syrup is unpalatable. Sodium picosulfate. Bisacodyl. Dantron (terminal care only)

Resources

• Constipation (BNF)​, Laxatives (NHS Choices)