For all solid oral dose products package development is an integral part of development. For modified release dosage formulations, containing pellets, beads, granules or coated granules, pharmaceutical packaging development can be absolutely key to ensuring therapeutic performance through shelf life stability.
Blister packing is still the predominant unit dose packaging format (though strip packaging, where the dosage form is packaged in individual connected pouches, separated by a foil strip, may be making a small comeback). Depending on your API, understanding the acceptable Water Vapor Transmission rate (WVT) for your product is an essential starting point for designing a pharmaceutical packaging format that ensures product stability over your desired shelf life.
Depending on the requirements of the forming film may consist of a single uncoated polymer or be coated with an agent to decrease the WVT. If your dosage form is very moisture sensitive and not protected by a coated plastic, a laminate containing aluminium foil can be used as a forming film.
Aclar films have the lowest water vapor permeation compared to all other plastic films used in blister packaging and have thermoforming properties similar to plain PVC though it is also the most expensive.Despite narrow thermoforming temperatures and required cooling steps PP is increasingly popular. This popularity is due in part to it not suffering the environmental liability that PVC suffers in discharging hydrochloric acid during incineration. Unplasticised PVC has good thermoforming properties but may not provide good moisture protection for some products. After the forming process a 250 µm film will have a final thickness of 50 to 100 µm in some deep drawn pockets.The reduction in thickness will result in an increase in WVT.
No matter the forming film you choose to use, PVC,PP or PVDC coated PVC or laminations of PVC with PVDC, it is essential for a well designed functional blister package that your aluminium lidding material precisely fits your forming film. The lidding material should also have the required strength of the finished package, capable of being run on the blister packaging equipment.
The most important property that controls WVT rates in aluminium film is its porosity. Ensure your foil supplier takes suitable care to avoid deformation and pinholing during roll production. Using Fick’s law it can be shown that in 24 hours, with 90% RH on the outside of the pharmaceutical packaging and an initial humidity of 0% on the inside, 0.2 mg of water will penetrate the foil through a pinhole with a radius of 10 μm. The larger holes result from damage due to hard particles [e.g. aluminium oxide or titanium diboride. Foil porosity may be caused by inhomogeneities in the film because of localised deformation that occurs during the rolling process. Frequent roll changing helps in the production of high quality foil and is good practice.
Even with these precautions during shelf life of a blistered unit dose, moisture or gas can breach the barrier through heat seal fins and then through the walls. A heat seal and protective lacquer can act as additional barriers to transmission.