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  • Diarrhea is an increased frequency and decreased consistency of fecal discharge as compared with an individual’s normal bowel pattern. It is often a symptom of a systemic disease. Acute diarrhea is commonly defined as shorter than 14 days’ duration, persistent diarrhea as longer than 14 days’ duration, and chronic diarrhea as longer than 30 days’ duration. Most cases of acute diarrhea are caused by infections with viruses, bacteria, or protozoa, and are generally self-limited.


  • Diarrhea is an imbalance in absorption and secretion of water and electrolytes. It may be associated with a specific disease of the gastrointestinal (GI) tract or with a disease outside the GI tract.

  • Four general pathophysiologic mechanisms disrupt water and electrolyte balance, leading to diarrhea; (1) a change in active ion transport by either decreased sodium absorption or increased chloride secretion, (2) a change in intestinal motility, (3) an increase in luminal osmolarity, and (4) an increase in tissue hydrostatic pressure. These mechanisms have been related to four broad clinical diarrheal groups: secretory, osmotic, exudative, and altered intestinal transit.

  • Secretory diarrhea occurs when a stimulating substance (eg, vasoactive intestinal peptide [VIP], laxatives, or bacterial toxin) increases secretion or decreases absorption of large amounts of water and electrolytes.

  • Inflammatory diseases of the GI tract can cause exudative diarrhea by discharge of mucus, proteins, or blood into the gut. With altered intestinal transit, intestinal motility is altered by reduced contact time in the small intestine, premature emptying of the colon, or bacterial overgrowth.


  • The clinical presentation of diarrhea is shown in Table 23–1. Most acute diarrhea is self-limiting, subsiding within 72 hours. However, infants, young children, the elderly, and debilitated persons are at risk for morbid and mortal events in prolonged or voluminous diarrhea.

  • Many agents, including antibiotics and other drugs, cause diarrhea (Table 23–2). Laxative abuse for weight loss may also result in diarrhea.

TABLE 23–1Clinical Presentation of Diarrhea

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