Diarrhoea

Diarrhoea is the abnormal passing of loose or liquid stools, with increased frequency, increased volume, or both. It can be classified based on its duration into:

• Acute diarrhoea ≤14 days in duration, improving within 2-4 days
• Persistent diarrhoea >14 days and ≤30 days
• Chronic diarrhoea >30 days
• Invasive diarrhoea (dysentery) is characterised by visible blood in the stool, fever and abdominal pain

Acute diarrhoea is typically the result of an infection (e.g., Campylobacter enteritis), a side-effect of a drug (e.g. antibiotic), or as an acute symptom of a chronic gastro-intestinal disorder (e.g. Crohn's disease, irritable bowel syndrome, ulcerative colitis). It may also result from the presence of non-absorbed osmotically active solutes in the bowel lumen because of malabsorption of a meal (e.g., lactase deficiency, chronic pancreatitis) or motility disorders of the bowel wall. All acute episodes of diarrhoea should lead to consideration of ingestion of potentially infected food, recent starting of a new drug or foreign travel. Consideration should also be given as to whether it might be a manifestation of another illness and the assessment should also include questions about any 'red flag' symptoms such as unexplained weight loss, rectal bleeding, previous episodes of diarrhoea, or systemic illness.

Most incidences of acute diarrhoea will resolve spontaneously, so the principal aim of treatment is to prevent dehydration and support electrolyte balance. Where there is a risk of severe dehydration urgent action to replace fluid and electrolytes may be necessary. Antimotility drugs such as loperamide can be used to provide rapid control of symptoms. Other drugs used for diarrhoea: codeine phosphate and co-phenotrope (diphenoxylate) are opioid-type drugs that inhibit gut motility; methylcellulose (absorbs water from the bowel, thus reducing dehydration and solidifying loose stool); rifaximin.(a rifamycin antibacterial drug that can be used to treat what's commonly referred to as travelers' diarrhoea; the major causes of which are exposure to unusual food- or water-borne contaminants in foreign destinations).

Long-term or chronic diarrhoea (i.e., lasting for >30 days), is often associated with chronic medical conditions including irritable bowel syndrome (IBS), inflammatory bowel diseases (Crohn's disease and ulcerative colitis), malabsorption syndromes (e.g., celiac disease), and sometimes long-standing infections. There are effective treatments for almost all cases of chronic diarrhoea. The best approach is to treat the underlying cause of chronic diarrhoea. Where this does not achieve resolution, the goal is to achieve control over symptoms, and again antimotility drugs (loperamide, diphenoxylate/atropine) and antispasmodic drugs (mebeverine, sold as Colofac^® in the UK, and scopolamine butylbromide sold under the trade name Buscopan^®) are widely used medications in this setting. 

Further information about additional classes of antidiarrhoeal drugs has been curated in the Drugs/Gastrointestinal system module