While moisture in pharmaceutical packaging can have negative or even dangerous effects on its content, unpleasant odours are especially repellent to patients. Here, Ursula Hahn, head of product management, Sanner, Germany, looks at how both can be systematically prevented using suitable adsorbents – provided the right aspects are taken into account.
Many pharmaceutical products are sensitive to moisture, the effects of which are manifold and often pose a high risk to both drugs and patients. In the case of tablets, powders and effervescent tablets, the properties and texture may change, whereas gel capsules might dissolve, and blood or urine test strips may produce false or misleading results. In the worst case, the efficacy of drugs is reduced, or the analytical results are falsified, which can lead to an incorrect medication and impede successful therapy. In addition, many pharmaceuticals, especially analgesics such as acetylsalicylic acid, release specific molecules into the ambient air inside the packaging that can develop very unpleasant odours.
Only real data provides reliable results
The amount of humidity that penetrates the packaging is decisive for the stability of a moisture-sensitive drug. Around 65% of humidity ingress can be attributed to the packaging. Weak spots can be the packaging wall, the sealing surfaces between containers and closures, as well as the sealing seams of blister packs. Hence the choice of the primary packaging depends mainly on maintaining the optimum climate inside the packaging to ensure the required shelf life.
A holistic approach that considers all aspects of moisture ingress into a pharmaceutical packaging is indispensable. Relevant parameters such as material type, wall thickness, product moisture and production conditions, as well as differing climatic conditions and consumer behaviour must be observed when designing the packaging. To obtain reliable data, tests should always be conducted with the actual packaging. Material datasheets or databases provide data determined under very specific and ideal conditions. These cannot be transferred 1:1 to a specific packaging. Consequently, only real data and realistic analyses avoid unnecessary durability tests.
Desiccants: silica gel or molecular sieves
Depending on the area of application, different desiccants such as silica gel or molecular sieves can be used. Hygroscopic desiccants attract moisture and keep it away from the content. The most common desiccant, silica gel, contains small interconnected channels that open into pores on the surface and can absorb up to 36% of their own weight without altering their structure. The higher the relative ambient humidity, the higher the adsorption capacity.
Molecular sieves, on the other hand, are synthetically produced zeolites with a uniform pore diameter and a crystalline structure. Molecular sieves adsorb moisture corresponding to between 20- 22% of their own weight, almost independently of the relative ambient humidity. While silica gel brings moisture to a certain level, molecular sieves can achieve a climate of close to 0% relative humidity inside a closed packaging.
Activated carbon: far more than odour adsorption
When it comes to odour adsorption, activated carbon is particularly efficient: the surface of just one kilogram of activated carbon equals a 160-kilometre two-line highway. Activated carbon is made of organic material with high carbon content such as peat, wood or coconut shell. This material is slowly heated in an oxygen-depleted or oxygen-free environment to remove water and impurities. The surface increases significantly through further physical and chemical processing and creates a submicroscopic network of pores.
The extremely hygroscopic surface molecules actively search for other molecules they can bind to. Activated carbon attracts numerous chemical compounds by adsorption and thus binds bad odours. Moreover, activated carbon can adsorb residual solvents as well as organic and inorganic impurities that reach the headspace of bottles by evaporation.
Drop-in sachets: eliminating risks right from the start
There are many ways to equip packaging with the right type and amount of desiccants and/or activated carbon. The fundamental difference is how adsorbents are inserted into the packaging. More cost-intensive, integrated desiccants are found within the cap of a tablet tube or as a desiccant chamber in the package bottom or in the wall. Drop-in desiccant solutions are added directly into bottles or containers in different forms.
Desiccant sachets are particularly soft and flexible. They can be placed anywhere in the container without any risk of damaging the drugs and patients can easily distinguish the sachets from the drug, leading to a low risk of accidental ingestion. Sachet packs are ideally made of Tyvek, which offers both durability and breathability. It is also particularly tear-resistant and puncture-proof, eliminating the risk of product contamination due to desiccant leakage during filling or usage.
Desiccant capsules for 360-degree moisture protection
Desiccant capsules are small, cylindrical containers made of plastic and sealed with a cardboard disc. Desiccant canisters have a similar shape but are made entirely of plastic. Desiccant capsules that provide 360-degree moisture absorption are rarely to be found on the market. Thanks to the unique grid structure in the capsule wall, moisture adsorption is ensured without losing effectiveness, even if the capsule ends up on the cardboard side after filling. These capsules can adsorb up to 30% more moisture than conventional capsules and their tactile grid structure prevents confusion with drugs and ultimately accidental ingestion.
Drop-in capsules or canisters are available in different sizes and with different filling material. Depending on the moisture protection requirements of certain drugs, silica gel, molecular sieves or a combination of both can be used. A mixture of silica gel and activated carbon is the best choice for pharmaceuticals that require both odour adsorption and moisture protection.
Holistic approach for ultimate product protection
Regardless whether a product is to be protected against moisture by using silica gel, molecular sieves or a combination of both, or whether additional activated carbon is used for odour adsorption: all solutions must always be tested regarding suitability and regulatory compliance. Moreover, a holistic view based on real data is crucial. It is the only way to implement all technical and regulatory aspects quickly, efficiently and with high qualityIndividual, integrated or drop-in – all desiccant packaging solutions must be smoothly integrated into existing processes of pharmaceutical manufacturers.
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