Ors composition
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ORS oral rehydration solution WHO composition 2024
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Here is a complete breakdown of ORS composition based on authoritative textbook sources:
ORS (Oral Rehydration Solution) Composition
WHO Reduced-Osmolarity ORS (Current Standard since 2004)
Ingredients per litre of water (grams):
| Ingredient | Amount (g/L) |
|---|---|
| Sodium chloride (NaCl) | 2.6 g |
| Glucose, anhydrous | 13.5 g |
| Potassium chloride (KCl) | 1.5 g |
| Trisodium citrate, dihydrate | 2.9 g |
| Total | 20.5 g |
Electrolyte concentrations (mmol/L):
| Constituent | Concentration (mmol/L) |
|---|---|
| Sodium (Na+) | 75 |
| Chloride (Cl-) | 65 |
| Glucose | 75 |
| Potassium (K+) | 20 |
| Citrate | 10 |
| Total Osmolarity | 245 mOsm/L |
- Park's Textbook of Preventive and Social Medicine, p. 266
- Harrison's Principles of Internal Medicine 22E, Table 153-3
Why This Formulation?
Mechanism: Glucose enhances sodium absorption via the sodium-glucose cotransporter (SGLT1) in the intestinal mucosa. This coupled transport drives water reabsorption, which is the pharmacological basis of ORS - it works even in secretory diarrhea.
Historical evolution:
- Original WHO ORS used sodium bicarbonate as the base.
- Replaced by trisodium citrate because it is more stable in storage and produces less stool output (especially in cholera), likely by directly enhancing intestinal sodium and water absorption.
- Reduced osmolarity (245 mOsm/L vs. the old 311 mOsm/L) was adopted in 2004 after evidence showed it reduced:
- Unscheduled IV therapy need by 33%
- Stool output by 20%
- Vomiting by 30%
Old vs. New ORS (Comparison)
| Parameter | Old WHO ORS | New (Reduced) ORS |
|---|---|---|
| Sodium | 90 mmol/L | 75 mmol/L |
| Glucose | 111 mmol/L | 75 mmol/L |
| Osmolarity | 311 mOsm/L | 245 mOsm/L |
| Base | Bicarbonate | Citrate |
Homemade Emergency ORS (If packets unavailable)
Mix in 1 litre of safe water:
- 3.5 g (~1/2 teaspoon) of table salt (NaCl)
- 50 g of pre-cooked rice cereal OR 6 teaspoons of sugar (sucrose)
- Supplement potassium separately (orange juice, coconut water, banana)
(Harrison's, p. 1372)
Key Points for Exams
- SGLT1 co-transport is the mechanism (Na+ and glucose absorbed together).
- India was the first country to launch the new formulation (June 2004); UNICEF adopted it from January 2004.
- Rice-based ORS is considered superior to standard ORS specifically for cholera.
- Pedialyte contains only 45 mEq/L sodium (less ideal than WHO formula); Rehydralyte is closest to WHO formula among commercial products.
- ORS is effective in all age groups, all causes of acute diarrhea, and can treat 90-95% of cholera/acute diarrhea cases without IV fluids.
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