Trisodium citrate (ORS)

Trisodium citrate (ORS) is the sodium salt of citric acid used in oral rehydration solutions to replace bicarbonate and help correct metabolic acidosis.

Function in oral rehydration

When severe diarrhea causes dehydration, it also leads to a loss of bicarbonate and accumulation of acid in the blood. Early oral rehydration formulas used sodium bicarbonate to correct this acidosis, but bicarbonate reduces the shelf life of the powder and is less stable in humid environments. The World Health Organization replaced sodium bicarbonate with trisodium citrate in the standard and reduced‑osmolarity ORS. Each liter of low‑osmolarity ORS contains about 10 mmol of citrate. Once ingested, citrate is metabolized in the liver to bicarbonate, which helps neutralize excess acid. Trisodium citrate also contributes additional sodium without adding chloride, keeping the electrolyte balance within a safe range. Compared with bicarbonate, citrate improves taste and storage stability, making ORS sachets more practical in tropical climates. The combination of glucose, sodium, potassium, chloride and citrate in ORS harnesses the sodium–glucose co‑transport mechanism to rehydrate while restoring acid–base balance.

Uses beyond medical ORS

Citrate salts are used in food and beverage manufacturing as acidity regulators and flavor enhancers. In sports drinks, a small amount of sodium or potassium citrate can provide buffering capacity and a mild tartness. This can reduce the risk of stomach upset when consuming carbohydrate‑electrolyte beverages during exercise. However, too much citrate may have a laxative effect or alter the flavor profile. Athletes mixing their own rehydration solutions can include a pinch of trisodium citrate or use commercial powders that already contain it to support electrolyte balance. As always, testing a drink during training is essential before relying on it in competition.

By substituting trisodium citrate for bicarbonate, modern oral rehydration solutions achieve long shelf life and effective correction of acidosis while supplying sodium in a palatable form.

Related Terms: Reduced‑osmolarity ORS, WHO sodium target (ORS), Glucose–sodium co‑transport, Dilution ratio, Custom blend

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