Solar Disinfection of Drinking Water and Oral Rehydration Solutions
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Disinfection Guidelines for Household Application in Developing
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Foreword
Oral Rehydration Therapy: The Revolution for Children
Oral Rehydration Therapy: The Four Simple Technologies
Global Rehydration Therapy: Global Diarrhoeal Diseases Control Programmes
Oral Rehydration Therapy: Causes, Transmission, and Control of Childhood Diarrhoea
Oral Rehydration Solutions: The Practical Issues
Oral Rehydration Solutions: Domestic Formulations
Oral Rehydration Solutions: Disinfection by Boiling
Solar Energy: Fundamental Considerations
Solar Energy: From Sun to Earth
Solar Energy: World Distribution
Solar Energy: A Competitor
Solar Energy: Some Practical Hints
Solar Disinfection Studies: Drinking Water
Solar Disinfection Studies: Oral Rehydration Solutions
Appendix: Source of Information on Diarrhoeal Diseases
Oral Rehydration Solutions
The Practical Issues
WHO/UNICEF Standard Formulation
Since 1971, WHO and UNICEF began to promote the use of a
standard formulation for the preparation of oral rehydration
solutions, widely regarded as the physiologically most appropriate
single formulation for world-wide use. It consists of the following
active ingredients mixed in dry form for making one litre of solution:
| Glucose, anhydrous |
20.0 grammes |
| Sodium chloride |
3.5 grammes |
| Sodium bicarbonate |
2.5 grammes |
| Potassium chloride |
1.5 grammes |
|
| Total weight |
27.5 grammes |
Oral
Rehydration Salts (ORS) -- formerly Oralyte. The use of
Aerosil (colloidal silicon dioxide) as an excipient in the
proportion of 2 grammes per kilogramme of ORS is optional. Aerosil is
harmless in this concentration, but renders the ORS solution very
slightly turbid. There are a number of alternative preparations that
do not comply in composition with the WHO/UNICEF formulation. These
have not yet been clinically evaluated.
For reconstitution of the standard formulation when required to be
given by mouth, the contents of one ORS packet are to be dissolved in
one litre of clean drinking water. UNICEF recommends boiling the water
and allowing it to cool before using it for the preparation of the
solution as hot water is apt to decompose the sodium bicarbonate.
When the content of one ORS packet is dissolved in one litre of water,
the following concentrations of the active ingredients are obtained:
|
Glucose
|
111 m mol/litre |
|
Sodium (Na+)
|
90 m mol/litre |
|
Chloride (Cl-)
|
80 m mol/litre |
|
Bicarbonate (HCO3)
|
30 m mol/litre |
|
Potassium (K+)
|
20 m mol/litre |
Production and Distribution
Out of an estimated two billion packets of standard ORS believed to be
needed annually for dehydration control throughout the world, only
about 80 million are being produced for distribution. Since 1981,
UNICEF has been distributing about 20 million packets annually at US
$0.08 per one-litre packet, including freight, in an attempt to meet
the partial national requirements of 87 nations. Together with WHO, it
has continued to encourage national and regional production. By
December 1982, 30 developing countries were producing ORS with the
assistance of WHO and UNICEF. Brazil alone is now producing some 20
million packets a year, and Pakistan has increased its annual
production to 5 million packets. On its part, WHO has recently
published a very instructive manual (Guidelines for the Production
of Oral Rehydration Salts) which includes specifications,
methodology, and quality control.
Some of the countries producing packets of ORS under different brand
names include Costa Rica (Sueroral), Tunisia (Orasol),
Egypt (Rehydran), Honduras (Litrosol), and Peru
(Salvadora). Packets with amounts of ORS smaller than the
standard formula are being produced in some countries for practical
reasons. In Costa Rica, for instance, Sueroral packets are intended
for 240 ml of solution. Such alternative products are more expensive
than the UNICEF packets, and can only reach a small minority of
users. Besides, the contents may not be uniform in composition or
weight. Other shortcomings include the use of packaging materials that
are difficult to open, or powders that do not dissolve readily. Some
products may have a poor shelf life. These difficulties may discourage
some families from using the local products.
The Program for Appropriate Technology in Health (PATH) in
Seattle, Washington, USA, has recently developed ORS tablets. These
PATH ORS TABLETS, 2.5 cm in diameter and weighing 5 grammes,
are currently formulated to make 150 ml of rehydration solution. The
tablet formula complies with the WHO standard formulation except that
sodium citrate is substituted for sodium bicarbonate to provide the
tablets with greater stability and a shelf life of at least one year
in polyethylene packages, and even more if foil-laminated packaging
material is used.
Modified WHO Formulations
PATH is promoting the local production of these tablets, and is
prepared to help in the transfer of the technology for production in
developing countries. In fact, by February 1984, PATH was in the
process of transferring the production technology to a company in
Indonesia and to another in Thailand. Other technology transfer
arrangements in Latin America are presently under consideration.
Some ingredients in the standard ORS formulation may be substituted
for in-country packet production, or preparation of homemade
solutions, without essentially altering the therapeutic effects on
rehydration. Selection of substitutes is determined by such additional
factors as availability, relative cost, and prolongation of the shelf
life.
Some commercial preparations used for oral rehydration contain sodium
citrate in place of sodium bicarbonate to achieve a longer shelf life,
although the latter is preferred because of lower cost and greater
availability.
WHO is continuing its interest in improving the shelf life of the ORS
ingredients by appropriate substitution of ingredients and packaging
materials. This has been evoked by evidence from field experience
indicating that packaged ORS is subject to deterioration due to the
reaction of glucose with sodium bicarbonate leading to the formation
of a brownish discolouration and lumping of the ingredients.
Although standard ORS in laminated aluminium foil packets have an
estimated shelf life of at least three years, their storage in
developing countries with extremely hot and/or damp climates are
likely to accelerate deterioration and caking of the ORS mixtures. In
an effort to overcome such a problem, WHO has developed three
alternative formulations that need to be tested for stability and
effectiveness. Sodium bicarbonate is substituted by sodium citrate in
two of these alternative formulations, and by potassium citrate in the
third.
Deterioration on Storage
At the request of WHO, the Central Laboratory of German
Pharmacists in Frankfurt has carried out accelerated stability
tests on the four ORS formulations developed by WHO made from
ingredients of pharmacopoeial purity, with and without packaging in
polyethylene foil or laminated aluminium foil. The results, reported
in June 1983 (Pharmazeutische Zeitung), indicate that both
humidity and temperature tend to promote deterioration. The percentage
absorption of moisture that leads to lumping of the ingredients may
reach as high as 10% for anhydrous glucose, 80% for potassium citrate,
and 140% for sodium chloride. Sodium bicarbonate starts to decompose
at temperatures above 40°C with evolution of carbon dioxide gas which
may cause some packets to burst during storage. Significant changes in
colour and consistency were observed at storage temperatures exceeding
40°C. Unlike the formulation with sodium bicarbonate, those with
sodium or potassium citrate as substitutes proved to be more
chemically stable. The conclusion is that glucose and sodium
bicarbonate in standard ORS packets, when stored at high temperatures
or humidity, would interact and undergo considerable decomposition. By
replacing bicarbonate with citrate, a more stable ORS mixture can be
obtained.
Laminated aluminium foil proved to be the best packaging material
for long-term storage in extremely damp climates, whereas polyethylene
foil is preferable for dry and hot climates as its permeability allows
drying and stabilization of the ORS mixture during storage. The choice
of packaging material, therefore, depends mainly on a country's climatic
conditions. Because polyethylene foil is transparent, however, ORS
packets can be checked visually for signs of glucose decomposition
accompanied by discolouration and lumping. Therefore, the use of
polyethylene packets can be a compromise for world-wide distribution.
It is thus concluded from this study that the formulation prescribed
below is recommended for large-scale production because of its much
slower rate of deterioration, and therefore potentially longer shelf life, in
preference to the other three ORS formulations developed by WHO:
| Glucose, anhydrous |
20.0 grammes |
| Sodium citrate
(C6H5Na3O7.2H2O) |
2.9 grammes |
| Sodium chloride |
3.5 grammes |
| Potassium chloride |
1.5 grammes |
|
| Total weight |
27.9 grammes |
kangaroo packets, were
shown to be effective for storage for as long as nine months in
adverse field conditions without detectable changes in the
components. They are useful therefore in areas where the usage rates
of ORS solutions are low, provided clear instructions are given for
their proper preparation.
Because high temperatures and humidity would accelerate the
deterioration process, manufacturers must consider these factors when
preparing and packing ORS. The packaged product must be properly
stored until distributed for use, preferably at temperatures and
humidity not exceeding 30°C and 80 percent, respectively. Batches
showing signs of deterioration upon inspection (lumping, turning
brown, and difficulty in dissolving) should be discarded. If the ORS
packets have only turned yellow, and can still be readily dissolved,
they are considered to be still effective and safe to use.
Sucrose as a Substitute
WHO has proposed using 40 grammes of common sugar (sucrose), if
justified by availability and cost, in place of the 20 grammes of
glucose prescribe in the standard ORS formulation. Although glucose is
preferred if it is available at comparable cost, studies have shown
common sugar to be almost as effective as glucose for rehydration. In
Bangladesh, for instance, substantial savings in cost were achieved by
using a crude, locally produced sugar called gur as a substitute
for glucose of sucrose. It should be noted, however, that common sugar
bought from local markets is sometimes adulterated with water to
increase the selling weight, its world priced have fluctuated
dramatically in recent years, and shortages are not uncommon in some
of the developing countries as is the case in Ghana and Tanzania.
Flavouring Additives
ORS solutions, when properly prepared from UNICEF packets, taste
slightly less salty than human tears. Since this is sometimes
considered by some to be an unpleasant taste, various flavouring
substances have been proposed for addition to ORS to improve the
palatability of the solutions. Apart from substantially raising the
cost of manufacturing the ORS formulation, solutions with specific
artificial flavours do not necessarily appeal to all users.
In a field study carried out in Ankara, Turkey, in 1979, a greater rate
of acceptability for the product was observed among children give
solutions made from ORS packets supplied by UNICEF compared to those
prepared from locally produced packets.
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