WHO ORS Preparation
WHO Oral Rehydration Solution (ORS) should be mixed by dissolving one packet containing 3.5g sodium chloride, 2.9g trisodium citrate, 1.5g potassium chloride, and 20g glucose in exactly 1 liter (1000 mL) of clean drinking water. 1, 2
Standard WHO-ORS Formula
The WHO-recommended formulation creates a solution with the following concentrations when properly mixed 1:
- Sodium: 90 mEq/L (or mmol/L)
- Potassium: 20 mEq/L
- Chloride: 80 mEq/L
- Bicarbonate (as citrate): 30 mEq/L
- Glucose: 111 mmol/L
- Total osmolarity: 311 mOsm/L 3
Critical Mixing Instructions
The exact volume of water is crucial—always use 1 liter (1000 mL) of clean water per packet. 1, 2
Common Pitfalls to Avoid:
- Never mix with inappropriate volumes of water, as this creates solutions that are either too diluted (ineffective) or too concentrated (potentially dangerous) 1
- Provide detailed written and oral instructions when packets are dispensed for home mixing 1
- The bicarbonate component has been replaced with citrate in modern formulations because citrate has a longer shelf life and is equally efficacious 1
Alternative Preparation Method
If commercial packets are unavailable, a pharmacy can prepare WHO-ORS by mixing 1:
- 3.5g sodium chloride (NaCl)
- 2.9g sodium citrate (or 2.5g sodium bicarbonate)
- 1.5g potassium chloride (KCl)
- 20g glucose (or 40g sucrose/4 tablespoons sugar, or 50-60g cooked cereal flour)
- Per 1 liter of clean water
Reduced-Osmolarity Formulations
More recent evidence supports reduced-osmolarity ORS (245 mOsm/L) containing 75 mmol/L each of sodium and glucose, which has shown superior outcomes in non-cholera diarrhea 4, 5. This formulation reduces stool output by 36% and decreases vomiting compared to standard WHO-ORS 5. However, the standard WHO formulation remains widely used and effective 1, 2, 3.
Practical Considerations
- Premixed commercial solutions (like Pedialyte) eliminate mixing errors but cost more 1
- Packets are preferred in resource-limited settings due to low cost, long shelf life, and ease of transport 1
- Always use clean drinking water for reconstitution 1, 2
- Once mixed, the solution should be used within 24 hours if kept at room temperature 1