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May 10, 2002
ORAL REHYDRATION SALTS (ORS)
A NEW REDUCED OSMOLARITY FORMULATION
For more than 25 years WHO and UNICEF have recommended a
single formulation of glucose-based Oral Rehydration Salts (ORS) to prevent or
treat dehydration from diarrhoea irrespective of the cause or age group
affected. This product, which provides a solution containing 90 mEq/l of sodium
with a total osmolarity of 311 mOsm/l, has proven effective and without apparent
adverse effects in worldwide use. It has contributed substantially to the
dramatic global reduction in mortality from diarrhoeal disease during the
period.
For the past 20 years, numerous studies have been undertaken
to develop an “improved” ORS. The goal was a product that would be at least
as safe and effective as standard ORS for preventing or treating dehydration
from all types of diarrhoea but which, in addition, would reduce stool output or
have other important clinical benefits. One approach has consisted in reducing
the osmolarity of ORS solution to avoid possible adverse effects of
hypertonicity on net fluid absorption. This was done by reducing the solution’s
glucose and salt (NaCl) concentrations .
Studies to evaluate this approach were reviewed at a
consultative technical meeting held in New York (USA) in July 2001 1, and
technical recommendations were made to WHO and UNICEF on the efficacy and safety
of reduced osmolarity ORS in children with acute non-cholera diarrhoea, and in
adults and children with cholera.
These studies showed that the efficacy of ORS solution for
treatment of children with acute non-cholera diarrhoea is improved by reducing
its sodium concentration to 75 mEq/l, its glucose concentration to 75 mmol/l,
and its total osmolarity to 245 mOsm/l. The need for unscheduled supplemental IV
therapy in children given this solution was reduced by 33%. In a combined
analysis of this study and studies with other reduced osmolarity ORS solutions (osmolarity
210-268 mOsm/l, sodium 50-75 mEq/l) stool output was also reduced by about 20%
and the incidence of vomiting by about 30% 1. The 245
mOsm/l solution also
appeared to be as safe and at least as effective as standard ORS for use in
children with cholera.
The reduced osmolarity ORS containing 75 mEq/l sodium,
75 mmol/l glucose (total osmolarity of 245 mOsm/l) is as effective as standard
ORS in adults with cholera. However, it is associated with an increased
incidence of transient, asymptomatic hyponatraemia. This reduced osmolarity ORS
may be used in place of standard ORS for treating adults with cholera, but
careful monitoring is advised to better assess the risk, if any, of symptomatic
hyponatraemia.
Because of the improved effectiveness of reduced
osmolarity ORS solution, especially for children with acute, non-cholera
diarrhoea, WHO and UNICEF now recommend that countries use and manufacture the
following formulation in place of the previously recommended ORS solution with a
total osmolarity of 311 mOsm/l.
1 Reduced
osmolarity oral rehydration salts (ORS) formulation
Report from a meeting of experts
jointly organised by UNICEF and WHO. WHO/CAH/01.22
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Reduced osmolarity ORS |
grams
/litre |
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Reduced osmolarity ORS |
mmol/
litre |
|
Sodium chloride |
2.6 |
Sodium |
75 |
|
Glucose, anhydrous |
13.5 |
Chloride |
65 |
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Potassium chloride |
1.5 |
Glucose, anhydrous |
75 |
|
Trisodium citrate dihydrate |
2.9 |
Potassium |
20 |
| |
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Citrate |
10 |
| Total Weight |
20.5 |
Total Osmolarity |
245 |
Although this single ORS formulation is recommended,
WHO and UNICEF have previously published criteria, which remain unchanged, for acceptable
ORS formulations. These criteria are listed below; they specify the desired
characteristics of the solution after it has been prepared according to the
instructions on the packet:
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The total substance concentration |
(including that contributed by glucose)
should be within the range of
200-310 mmol/l |
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The individual substance concentration |
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Glucose |
should at least equal that of sodium but
should not exceed 111 mmol/l |
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Sodium |
should be within the range of 60-90 mEq/l |
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Potassium |
should be within the range of 15-25 mEq/l |
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Citrate |
should be within the range of 8-12 mmol/l |
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Chloride |
should be within the range of 50-80 mEq/l |
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