What is the recommended composition of Oral Rehydration Solution (ORS)?

Recommended Composition of Oral Rehydration Solution (ORS)

The recommended ORS composition for rehydration should contain 75-90 mEq/L of sodium, 20 mEq/L of potassium, 65-80 mEq/L of chloride, 10 mEq/L of citrate, and 75-111 mmol/L of glucose (2-2.5%), with a total osmolarity of 245-311 mOsm/L. 1, 2, 3

Different ORS Formulations Based on Clinical Need

Rehydration ORS (for treating dehydration)

• Sodium: 75-90 mEq/L
• Potassium: 20 mEq/L
• Chloride: 65-80 mEq/L
• Citrate: 10 mEq/L (replaces bicarbonate for longer shelf life) 1
• Glucose: 75-111 mmol/L (2-2.5%)
• Total osmolarity: 245-311 mOsm/L

Maintenance ORS (for preventing dehydration)

• Sodium: 40-60 mEq/L
• Potassium: 20 mEq/L
• Other components: Similar to rehydration ORS
• Usage: For prevention of dehydration or maintenance after initial rehydration 1, 4

Evolution of ORS Composition

Traditional WHO-ORS (Standard)

• Sodium: 90 mmol/L
• Glucose: 111 mmol/L (2%)
• Total osmolarity: 311 mOsm/L
• Historical context: This was the standard formulation until early 2000s 3

Reduced Osmolarity ORS (Current WHO Recommendation)

• Sodium: 75 mmol/L
• Potassium: 20 mmol/L
• Chloride: 65 mmol/L
• Citrate: 10 mmol/L
• Glucose: 75 mmol/L
• Total osmolarity: 245 mOsm/L
• Benefits: 33% reduction in need for unscheduled IV therapy compared to standard ORS 5, 3

Clinical Decision-Making for ORS Selection

For Severe Dehydration or High-Output Diarrhea

• Use higher sodium concentration (75-90 mEq/L) 1
• Indicated when purging rate exceeds 10 mL/kg/hour
• Consider IV rehydration for grade 3-4 diarrhea or signs of severe dehydration 1

For Mild to Moderate Dehydration

• Lower sodium solutions (40-60 mEq/L) are appropriate 1
• Commercial products like Pedialyte (45 mEq/L sodium) and Ricelyte (50 mEq/L sodium) are suitable 1

For Maintenance After Rehydration

• Use 40-60 mEq/L sodium solutions 1, 4
• When using solutions with >60 mEq/L sodium for maintenance, supplement with low-sodium fluids (breast milk, formula, water) to prevent sodium overload 1

Important Considerations

Safety Precautions

• Hypernatremia risk: Solutions with high glucose content (>2.5%) or hyperosmolar foods can increase risk of hypernatremia 6
• Hyponatremia monitoring: No significant difference in hyponatremia incidence between reduced osmolarity and standard ORS 5
• Proper mixing: When using ORS packets, ensure correct dilution with appropriate volume of clean water to avoid over-concentration 1, 7

Special Formulations

• Rice-based ORS: Contains rice powder or rice-syrup solids instead of glucose
• Benefits: May reduce stool output in early hours of treatment
• Limitations: Difficult to standardize when home-prepared; may become contaminated if left unrefrigerated 1

Administration Guidelines

• For children: 100-200 mL after each stool for a 3-year-old child 2
• For adults with diarrhea: 2200-4000 mL/day 1
• Administer in small, frequent volumes for patients with vomiting (5 mL every minute) 2

Efficacy Evidence

Recent systematic reviews show that reduced osmolarity ORS (≤245 mmol/L) compared to standard ORS results in:

• Decreased duration of diarrhea
• Reduced stool output
• Lower ORS intake requirements
• Comparable cure rates 3

These findings support the current WHO recommendation for reduced osmolarity ORS as the preferred formulation for treating diarrheal illness in children.