Oral rehydration therapy

ORT has two related purposes: an initial rehydration phase replaces fluid and electrolyte deficits, and a maintenance phase replaces continuing losses while appropriate nutrition is maintained. The treatment is usually delivered as ORS, a measured mixture of glucose and salts dissolved in safe water. It is not simply water: its composition is intended to replace sodium and other electrolytes while supporting absorption of fluid from the intestine.

ORT is used particularly for dehydration associated with acute diarrhoea and gastroenteritis. Its suitability depends on the patient's condition. Severe dehydration, shock, altered consciousness, or an inability to drink requires urgent clinical assessment and may require intravenous fluids; ORS can still be given when clinically appropriate.

The physiological basis of ORS is the coupled transport of sodium and glucose across the intestinal lining. This transport can remain effective during diarrhoeal illness, allowing water to follow absorbed solutes. ORS therefore uses glucose together with sodium and other electrolytes rather than relying on plain water alone.

WHO and UNICEF moved from the earlier standard formulation to a reduced-osmolarity formulation. The expert report describes a commonly recommended composition of 75 mmol/L glucose, 75 mEq/L sodium and a total osmolarity of 245 mOsm/L, with potassium, chloride and citrate also included. Lower osmolarity ORS was intended to improve treatment outcomes while preserving the central rehydration mechanism.

Controlled evidence summarized in a Cochrane review found that, in children hospitalized with acute diarrhoea, reduced-osmolarity ORS was associated with fewer unscheduled intravenous fluid infusions than the earlier WHO standard solution. The review also found lower stool output and less vomiting in the reduced-osmolarity group, without detecting an additional risk of hyponatraemia compared with the standard solution in the included studies.

ORT does not stop every cause of diarrhoea, and it does not replace assessment of the underlying illness. WHO and UNICEF guidance describes ORS alongside continued breastfeeding or feeding when appropriate, safe fluids, and selective use of other treatments. UNICEF also reports that zinc supplementation with ORS for children with diarrhoea can reduce episode duration and severity; zinc is an adjunct, not a substitute for rehydration.

The modern history of ORT grew from work in the 1960s on treating diarrhoeal dehydration with oral glucose–electrolyte solutions. WHO and UNICEF adopted and promoted ORS and oral rehydration therapy internationally in the late 1970s. Over time, clinical studies led to the lower-sodium, reduced-osmolarity formulation now recommended by international health agencies.

ORT is significant because it can be administered without specialized equipment in many cases and can be manufactured and distributed at relatively low cost. Its effectiveness depends on correct preparation, safe water, timely administration and referral when illness is severe.