SDL Assignment - PH 6.3: Types of ORS and Their Compositions

1. Introduction

2. Physiological Basis (Mechanism of Action)

• In secretory diarrheas (cholera, ETEC), the Na+/K+ ATPase and SGLT1 co-transporter on enterocytes remain functional.
• Glucose (an actively transported substrate) couples with Na+ at the SGLT1 transporter on the luminal membrane of the small intestine.
• For every glucose molecule absorbed, 2 Na+ ions (and accompanying water) are absorbed.
• This compensates for the secretory losses driven by cholera toxin or other enterotoxins.
• Key principle: Glucose does NOT enhance absorption in the ileum or colon to the same extent, so jejunal segment is the primary site.

3. Types of ORS and Their Compositions

Type 1: WHO Original (Standard) ORS - 1975/1980s (Now Outdated)

• High sodium (90 mmol/L) - suitable for high-output secretory diarrhea like cholera
• Total osmolarity 311 mOsm/L (slightly hypertonic compared to plasma)
• Citrate replaced bicarbonate for better stability and reduced stool output
• Drawback: Risk of hypernatremia and edema in non-cholera diarrheas; now largely replaced

Type 2: WHO Reduced Osmolarity ORS (2002) - Current Recommended Standard

• Lower Na+ (75 vs. 90 mmol/L) and lower glucose (75 vs. 111 mmol/L)
• Total osmolarity 245 mOsm/L (hypotonic - reduces osmotic load on the gut)
• Compared to standard ORS:
  • Stool output reduced by ~20%
  • Need for unscheduled IV therapy reduced by ~33%
  • Vomiting reduced by ~30%
• Safe and effective for both non-cholera diarrhea and cholera in adults and children
• Currently the only WHO/UNICEF recommended ORS formulation

Type 3: Rice-Based (Polymer-Based) ORS

• Lower osmolarity per glucose equivalent delivered
• Patient acceptance is high
• Stool output is reduced (superior to standard WHO ORS)
• May be cost-effective
• Studies suggest it is superior to standard WHO-ORS, but its superiority over reduced-osmolarity ORS is not clearly established
• Particularly useful in cholera (rice-based ORS is considered superior to standard ORS in cholera)

Type 4: ReSoMal (Rehydration Solution for Malnourished Children)

• Reduced Na+ (to avoid sodium overload and edema in malnourished states with poor cardiac reserve)
• Increased K+ (to correct severe hypokalemia common in malnutrition)
• Contains micronutrients (zinc, magnesium, copper)
• Available in UNICEF packets; used under WHO guidelines for SAM (Severe Acute Malnutrition) with diarrhea

Type 5: Commercial ORS Formulations (Pediatric Electrolyte Solutions)

Type 6: Home-Available Fluids (Informal ORS)

• Home-made ORS (1 glass / 200 mL): 1 level teaspoon salt + 8 level teaspoons sugar in 1 liter clean water
• Thin rice water (kanji)
• Coconut water
• Diluted lassi (yogurt-based drink)
• Not recommended: Fruit juices (high osmolarity ~730 mOsm/L), carbonated drinks (Coca-Cola ~650 mOsm/L), sports drinks (Gatorade ~350 mOsm/L, inadequate electrolytes) - these worsen diarrhea due to high osmolarity

4. Comparative Summary Table

5. Key Points for Exam (Lippincott & KDT Perspective)

1. Mechanism: Glucose-Na+ co-transport (SGLT1) in the small intestine is the pharmacological basis. This is unaffected by secretory diarrhea toxins.
2. Evolution of ORS:
   • Original: Sodium bicarbonate-based → replaced by trisodium citrate (more stable, less stool output)
   • Standard (311 mOsm/L) → Reduced osmolarity (245 mOsm/L) in 2002
3. Reduced Osmolarity ORS advantages over standard ORS:
   • 20% reduction in stool output
   • 33% reduction in need for IV fluid supplementation
   • 30% reduction in vomiting
   • No increased risk of hyponatremia (despite lower Na+ content)
4. Why trisodium citrate replaced sodium bicarbonate:
   • Better stability on storage
   • Direct effect on increasing intestinal absorption of Na+ and water
   • Reduced stool output, especially in high-output diarrheas (cholera)
5. Rice-based ORS: Polymer hydrolysis yields multiple glucose molecules per osmole → better Na+ and water absorption without osmotic penalty.
6. Drugs NOT needed with ORS in most diarrheas: Antidiarrheal drugs (loperamide, diphenoxylate), antiemetics (usually), antibiotics (most viral/self-limited diarrheas).
7. Zinc supplementation (10-20 mg/day for 10-14 days) is recommended alongside ORS in children under 5 years with acute diarrhea (WHO/UNICEF guidelines) - reduces duration and severity of diarrhea episodes.

6. Contraindications / When NOT to Use ORS

• Severe dehydration (>10% body weight loss) - use IV fluids first
• Ileus or intestinal obstruction
• Unconscious/uncooperative patient
• Persistent vomiting making oral hydration impossible
• Hypernatremia or severe electrolyte imbalance requiring close monitoring

References

1. Lippincott Illustrated Reviews: Pharmacology (GI chapter - ORT/ORS)
2. KDT - Tripathi's Essentials of Medical Pharmacology (GI Pharmacology chapter)
3. Park's Textbook of Preventive & Social Medicine - Diarrhoeal Disease Control Programme (p. 266)
4. Sleisenger & Fordtran's Gastrointestinal and Liver Disease - Table 110.6: Composition of Various Types of ORS
5. Tintinalli's Emergency Medicine - Table 19-9: Composition of Standard and Reduced-Osmolarity ORS
6. WHO/UNICEF Joint Statement on Reduced Osmolarity ORS (2002)
7. Harrison's Principles of Internal Medicine 22e - Cholera and Infectious Diarrhea

Submission reminder: This assignment is due 13/07/2026. Ensure you write answers in your own words - the above is a study guide. Diagrams showing the SGLT1 mechanism and a comparison table of ORS types are strongly recommended in your submission.