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Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Oral Ondansetron to Assist Oral Rehydration Therapy

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Oral rehydration can be a lifesaving therapy for persons, particularly children, suffering from dehydration. The most common cause of dehydration in children is infectious diarrhea.

When dehydration occurs, it is important to act swiftly. If fluid losses are significant, begin to replace liquids as soon as you can.

Oral Rehydration Salts (ORS) that meet World Health Organization standards are available in a dry mix; use one packet per quart (liter) of water. One packet contains sodium chloride 3.5 grams, potassium chloride 1.5 g, glucose 20 g, and trisodium citrate 2.9 g (or sodium bicarbonate 2.5 g). Cera Lyte 70 oral rehydration salts are based on a rice solution. One packet is mixed with a quart (liter) of water. After the solution is prepared, it should be consumed or discarded within 12 hours if kept at room temperature or 24 hours if kept refrigerated. Other ORS products available over-the-counter include Pedialyte, Enfalyte, Naturalyte, and Rehydralyte.

1. Mild diarrhea/hydration: Drink soda water, clear juices, broth, and electrolyte-containing sports beverages. If diarrhea is the cause, try to replace each diarrheal stool with 10 milliliters of ORS per kilogram (2.2 pounds) of body weight. If the child is vomiting, try to replace each episode of vomiting with 2 mL of ORS per kg (2.2 lb) of body weight.

2. Moderate diarrhea/dehydration: Drink diluted (by half, with water) electrolyte-containing sports beverages, mineral water (bottled), or a homemade solution (1 quart or liter of disinfected water plus 1/2 to 1 teaspoon, or 1.3 to 2.5 mL, of sodium chloride [table salt], 1/2 tsp of sodium bicarbonate [baking soda], 1/4 tsp, or 0.6 mL, of potassium chloride [salt substitute], and glucose [6 to 8 tsp, or 30 to 40 mL, of table sugar; or 1 to 2 tbsp, or 15 to 30 mL, of honey]). Take care not to over-sweeten (exceed 2 to 2.5% glucose) the solution with sugar, because this may worsen the diarrhea; too high a sugar concentration inhibits water absorption through the gastrointestinal tract. Each quart of this “home brew” should be alternated with 1/2 to 1 quart of plain disinfected water. Try to replace fluid losses at least every 2 hours.

When using ORS, try to get the victim to ingest a quart per hour until the frequency of urination begins to increase and the urine color turns light or clear. To begin, start with small (e.g. 5 mL or one teaspoon) amounts every 1 to 2 minutes, to avoid collection of a large amount of fluid in the stomach that might cause vomiting. A child should be given 11/2 oz (44 mL) of ORS per pound (0.45 kg) of body weight over the first 4 hours, then 1 ounce (30 mL) of ORS per pound of body weight per 8-hour period until the diarrhea resolves. Another estimate of fluid replacement for children is 100 ml (approximately 3 oz) of fluid per significant loose bowel movement. For an infant with diarrhea, decrease the amount of milk in the diet, and add more water, diluted juices, half-strength sports beverages, and ORS. Sweetened carbonated beverages (soda pop) are not good replacement fluids, because they contain too much sugar and little or no sodium and potassium. If the child is breast-fed, keep nursing (offer the breast more often). If the child is formula-fed, use ORS for 12 to 24 hours, then try switching back to formula. If the diarrhea persists switch back to ORS for another cycle. It is important to continue to provide nourishment with food (and calories) to children with diarrhea, not fluid alone. Avoid foods high in simple sugars (including tea, juices, and soft drinks). Try complex carbohydrates (rice, wheat, potatoes, bread, cereals) and yogurt, lean meat, fruits, and vegetables.

If premeasured salts are not available with which to supplement water, you can alternate glasses of the following two fluids, as recommended by the U.S. Public Health Service:

GLASS ONE — 8 oz fruit juice with 1/4 tsp (a “pinch”) table salt and 1/2 tsp honey or corn syrup (237 mL juice, 1.3 mL table salt, 2.5 mL honey or corn syrup)

GLASS TWO — 8 oz disinfected water with 1/4 tsp baking soda (sodium bicarbonate) (237 mL water, 1.3 mL baking soda)

Another homemade fluid mixture is 1 tsp (5 mL) table salt and 1 cup (275 mL) rice cereal in a quart (liter) of water; this must be used within 12 hours or discarded. If only fruit juice (without supplementation) is available, remember to cut it to half strength with water. Otherwise, the sugar content will be too high and may contribute to continued diarrhea. Estimation techniques to measure powdered ingredients (such as a “pinch” of table salt) are notoriously inaccurate, and can even be dangerous if you add excessive amounts. Use a proper measuring implement whenever possible.

3. Severe diarrhea/dehydration: Same as moderate. After a certain point, as with cholera, intravenous hydration may be lifesaving. See a physician as soon as possible.

Sometimes, offering liquids to drink is not sufficient to diminish the nausea and vomiting that accompany an episode of gastroenteritis. If a person cannot ingest sufficient liquid, the diarrhea persists. In a recent article in the Annals of Emergency Medicine (Ann Emerg Med 2008:52:22-29) entitled "The role of oral ondansetron in children with vomiting as a result of acute gastritis/gastroenteritis who have failed oral rehydration therapy: a randomized controlled trial," the authors concluded that in subjects with acute gastritis/gastroenteritis and mild to moderated dehydration who failed initial oral rehydration therapy, the proportion of children who subsequently required intravenous hydration was lower in a group treated with ondansetron (Zofran) in a dose of 0.15 mg/kg body weight of the oral dissolving tablet, as compared to a group that did not receive the drug.

Having suffered nausea and vomiting from acute infectious gastroenteritis while traveling, I can attest to the benefit of ondansetron in providing sufficient relief to allow me to be able to begin to drink liquids and thereby rehydrate. Given that this observation is fairly common among clinicians in the field, and that this study strongly points to a benefit of the drug for children in whom oral rehydration is prevented by persistent nausea and vomiting, it makes perfect sense to carry a drug such as this, with limited side effects, that might allow initiation of essential replenishment of body fluid.

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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