Pharmacology · Electrolytes and rehydration solutions
Oral rehydration salts !
A mix of salts and glucose dissolved in clean water that replaces fluid lost in diarrhoea. Cheap and life-saving, especially in children.
Updated 2026-11-01
Also called: ORS
Mechanism of action
In diarrhoea the gut loses water and electrolytes, but glucose-coupled sodium absorption usually keeps working. Glucose and sodium in the solution enter intestinal cells together through SGLT1, chloride and water follow, and the potassium and base (citrate) in the mix replace what was lost in the stool.
- Glucose and sodium enter the gut cell together via SGLT1
- Chloride and water follow the absorbed sodium
- Potassium and citrate replace losses in the stool
- Dehydration is corrected by mouth
Pharmacokinetics
- Absorption
- Absorbed in the small intestine, which replaces the water and electrolytes lost in the stool
- Onset and duration
- Rehydration starts within hours of regular sips
Indications
- Dehydration from acute diarrhoea in children and adults Acute (viral) gastroenteritis →
- Prevention of dehydration during diarrhoea, together with zinc in children
- Cholera, as the base of rehydration
Adverse effects
Common
- Vomiting, especially if drunk too fast
- Salt imbalance if prepared with the wrong amount of water
Contraindications
- Severe dehydration or shock, where IV fluids come first
- A patient who cannot drink or swallow safely
Key interactions
- Zinc supplements
- Given together in children: zinc shortens diarrhoea and reduces stool volume
What is monitored
- Signs of dehydration (thirst, skin turgor, eyes, alertness)
- Stools and vomiting
- Urine output
- Weight in children
Nursing care
- Assess the degree of dehydration before starting; severe dehydration or shock needs IV fluids.
- Prepare each sachet with exactly the volume of clean water on the pack, and use it within the time stated.
- Give small, frequent sips or spoonfuls; if the child vomits, wait a short while and continue more slowly.
- Continue breastfeeding and nutritious food during diarrhoea.
- Teach danger signs for return: blood in the stool, not drinking, lethargy, persistent vomiting.
Pregnancy and breastfeeding
Safe in pregnancy and breastfeeding; dehydration itself is the greater risk.
Test yourself
Think of the answer, then tap the question to see it.
Why does oral rehydration solution contain glucose?
Glucose and sodium are absorbed together through SGLT1 in the small intestine; water follows, so glucose makes sodium and water absorption work even during diarrhoea.
What does WHO add to oral rehydration salts for children with diarrhoea?
A course of zinc supplements, which shortens diarrhoea and reduces stool volume.
When is oral rehydration not enough?
In severe dehydration or shock, or when the patient cannot drink; IV fluids are needed.
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Diarrhoeal disease (World Health Organization, 2024); Oral rehydration salts (World Health Organization, 2006); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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