Effervescent tablets are solid pharmaceutical dosage forms designed to break in contact with liquid such as water or juice, often causing the tablet to dissolve into a solution. They are uncoated tablet preparations containing mixtures of medicinal agents with acid substances and carbonates or hydrogen carbonates, which react rapidly in the presence of water to release carbon dioxide.
Effervescent tablets are packaged in such a way that they are protected against moisture. This is accomplished with waterproof containers e.g., glass, plastic, metal tubes, or individual foil pouches joined to form a conveniently sized strip of tablets.
Glass offers the highest degree of moisture protection of the non-flexible packaging materials; however, inherent limitations exist, such as breakage and cost of shipping a heavy package.
Since individual packaging in glass is economically infeasible, moisture-proof closures for these multiple-use containers must be used. Metal caps with a waxed, aluminum foil, pulp backed cap liner usually prove satisfactory when repeatedly opened and closed. If properly closed after each use, moisture is excluded from the interior of the package.
Since moisture can enter a glass container only through the closure, desiccants are used to “bind-up” any free moisture in the tablet or in the air to prevent the effervescence reaction from starting prematurely.
Once opened, however, protection from moisture is diminished because the air space becomes greater and greater as the tablets are used.
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Plastic tubes are not as protective as glass due to the moisture vapor permeability of plastic packaging materials. Tablets with a low order of hygroscopicity can be satisfactorily packaged in plastic tubes with moisture-proof closures.
Special caps can be constructed with a chamber containing silica gel or some other desiccant that will preferentially absorb moisture vapor entering through the closure.
Extruded, seamless metal tubes, often made from aluminum, have been used commonly in Europe to package effervescent tablets. These are impervious to moisture as are glass tubes.
Effervescent tablets are most frequently strip-wrapped in individual pouches, arranged in conveniently sized strips, and stacked in a paperboard box. Each tablet is hermetically sealed in its own container and is not exposed to the atmosphere until the time of use.
Many different flexible packaging materials are available for packaging, but few are suitable for protecting effervescent tablets from moisture vapor or physical damage.
Some effervescent tablets are packaged in thermoformed plastic blisters with foil backing. This type of packaging requires that the tablets be pushed through the foil backing by pressing on the blister. The tablets packaged in this manner must be hard enough so as not to break when they are removed from their package.
Most large diameter, relatively thin effervescent tablets cannot be made hard enough to withstand the force required to remove them from this type of packaging.
Aluminum foil is a flexible, absolute barrier to gases, water vapor, and light. It is nontoxic and immune to microbiological attack. It has excellent heat conductivity, thereby making it an excellent choice for heat-sealing strip-packaging operations.
Foil packaging should be heavy gauge to minimize risk of holes, and the surrounding pocket should be large enough to hold the tablets but minimize inclusion of air.
To ensure that effervescent tablet produced reaches the ultimate user with the same quality as originally produced and packaged, tests are performed on the seal integrity of various packaging configurations. Clearly, the integrity of any package is only as good as its closure. For effervescent tablets, an impervious package with a loose-fitting cap or imperfect heat seal is as good as if the cap were left off or the heat seal area left unbounded. Hermetic packaging is required if effervescent tablets are to attain a reasonable shelf life of 2 to 3 years.
The ultimate testing procedure is to store packages for their expected shelf life under the most severe humidity and temperature conditions that they will encounter, once sold. Since this is not practical, accelerated testing procedures have been developed that simulate long-term storage in adverse environments.
Packages containing effervescent tablets are stored in test chambers regulated at constant high humidity and temperatures, such as 80% relative humidity at 37°C for at least 3 months. The package is considered satisfactory if the product shows little or no moisture pickup after being stored in a chamber.
Changes in moisture content with time can be monitored if the relative moisture content of the product is determined before the study is started. These changes may be due to moisture seeping into the product through the closure or through the package itself if it is made of a material not completely impervious to moisture-vapor transmissions, such as polyethylene bottles or thin aluminum foil with pinholes.
Obviously, one cannot afford the expense or the time to wait 3 months to test representative samples of the packages produced on a day-to-day basis; several methods to test seal integrity rapidly (especially seals of aluminum foil laminates) have been devised and these include