Recommended Composition of Oral Rehydration Solution (ORS)
Standard WHO-ORS Formulation
The World Health Organization and UNICEF recommend a single standardized ORS formulation containing (in mmol/L): sodium 90, potassium 20, chloride 80, base (citrate) 30, and glucose 111 (2%), with total osmolarity of 311 mOsm/L. 1
This composition represents a compromise between the higher sodium losses seen in cholera versus the lower losses in noncholera diarrhea, making it universally applicable across different etiologies and age groups. 1
Modern Low-Osmolarity Alternative
For children with acute noncholera diarrhea, a reduced osmolarity ORS containing sodium 75 mmol/L, potassium 20 mmol/L, chloride 65 mmol/L, citrate 10 mmol/L, and glucose 75 mmol/L (total osmolarity 245 mOsm/L) reduces the need for unscheduled intravenous therapy by 33% compared to standard WHO-ORS. 2, 3
Key advantages of reduced osmolarity formulation:
- Reduces stool output by 36% during rehydration phase 3
- Decreases vomiting episodes during rehydration (relative risk 2.4 for standard ORS vs. reduced osmolarity) 3
- Lowers treatment failure rates (relative risk 7.9 for needing IV fluids with standard WHO-ORS) 3
- Maintains safety profile with no significant increase in hyponatremia risk 2
Sodium Concentration Based on Clinical Context
For Active Rehydration (Moderate Dehydration):
- Use solutions containing 75-90 mEq/L sodium, particularly when purging rates exceed 10 mL/kg/hour 4, 5
- Higher sodium concentrations (90 mmol/L) are preferable for cholera and severe secretory diarrhea 1, 6
For Maintenance Therapy (After Rehydration):
- Use solutions containing 40-60 mEq/L sodium to prevent sodium overload 1, 5
- When using solutions with >60 mEq/L sodium for maintenance, provide additional low-sodium fluids (breast milk, water, or diluted formula) 1, 7
Commercially Available Products in the United States
Pedialyte (45 mEq/L sodium) and Ricelyte (50 mEq/L sodium) are the most widely used commercial preparations, designed primarily for maintenance hydration rather than active rehydration. 1
- These lower sodium formulations can be used for rehydration in mild cases but are suboptimal for moderate-to-severe dehydration 1, 7
- Solutions with 75-90 mEq/L sodium are preferable for rehydration but less commonly available commercially in the U.S. 1, 4
Critical Formulation Details
Base Component:
- Modern ORS uses citrate instead of bicarbonate for longer shelf life, with equivalent efficacy in promoting sodium and water absorption 1, 5
Glucose Concentration:
- Glucose should be 75-111 mmol/L (1.4-2%) to optimize sodium-glucose cotransport without causing osmotic diarrhea 1, 5
- Excessive glucose (>2.5%) increases risk of hypernatremia and osmotic diarrhea 6
Common Pitfalls to Avoid
Never use sports drinks (Gatorade), fruit juices (apple juice), or soft drinks for rehydration - these contain inappropriate electrolyte concentrations, excessive sugar, and inadequate sodium. 1, 5
Hypernatremia Risk Factors:
- Solutions with high glucose content (>2.5%) combined with high sodium 6
- Severe watery diarrhea in well-nourished infants <6 months 6
- Using maintenance solutions (90 mmol/L sodium) without supplemental low-sodium fluids 1
Monitoring Requirements:
- Watch for hyponatremia (serum sodium <130 mmol/L) when using reduced osmolarity ORS, though incidence remains low (4% with 75 mmol/L sodium vs. 2% with 90 mmol/L) 2
- In elderly patients with heart or kidney disease, monitor for fluid overload when using any ORS formulation 4, 7
Special Clinical Scenarios
For bloody diarrhea (dysentery), ORS alone is insufficient and antimicrobial treatment may be required. 4
For patients with intestinal ileus, withhold oral fluids until bowel sounds return. 4
For glucose malabsorption (rare, ~1% of cases), watch for paradoxical increase in stool output with ORS administration. 4