Tips for Freeze Drying in the Vial

We provide solutions to some of the most common complications associated with Freeze Drying your product in a vial. Such challenges include stoppers sticking to the freeze dryer shelves, 'fogging', and using the wrong sized vial.

Read our practical advice before embarking on your next lyophilisation project.

Why do we Freeze Dry Pharmaceuticals?

Many pharmaceutical products stored in the liquid state are susceptible to degradation due to their physicochemical and thermostability characteristics, as well as sensitivity to external factors such as light, heat and oxygen. Such products may become unstable, leading to a loss of efficacy. This creates a significant challenge for storage and logistics, and can have a detrimental effect on shelf life.

Lyophilisation, or freeze drying, is a process used in the pharmaceutical and biotech industries to stabilise a product, by initially freezing the liquid state formulation and subsequently removing the water through a series of sublimation and desorption steps. The resulting dried state product, or “cake”, can typically be stored for longer periods of time at higher temperatures, substantially reducing the costs associated with shipping, transportation and storage. The freeze-dried product may then be reconstituted with a diluent immediately prior to administration.

Lyophilisation is of particular benefit for drug products that are unstable in liquid form as it is relatively gentle compared to other drying methods, enabling the stability and shelf life of the product to be increased with minimal risk to heat labile products.

The Freeze Drying Process

There are three key stages to the freeze drying process; freezing, primary drying and secondary drying.

Freezing

During the first stage the drug and its excipients are subjected to below-freezing temperatures until completely frozen. In this stage the majority of water present forms a crystalline phase separate from the solutes, which typically remain in an amorphous state. Additional thermal treatment steps, such as annealing, may be employed to encourage ice crystal growth and networking or to promote crystallisation of other formulation components to create a frozen state composition that is more favourable for freeze-drying.

Primary Drying

The next stage is primary drying, in which the pressure in the chamber containing the frozen product is reduced to the point at which the ice present within the product sublimes to water vapour and escapes the vial. This vapor is subsequently deposited on a “condenser” located elsewhere in the freeze-dryer.

Secondary Drying

In the final stage, the temperature of the product is increased to remove the remaining residual water by desorption. The dried powder remaining after the drying steps are complete is commonly known as a freeze dried ‘cake’.

Fogging

Fogging is an issue commonly encountered when freeze drying. It presents as powder deposits on the inside walls of the vial, giving a ‘foggy’ appearance to the glass, and occurs when residual liquid adheres to the internal surface of the vial prior to lyophilization. Antibody drug conjugates (ADCs) are especially liable to fogging during lyophilisation.

Aside from being visually unappealing, and leading to rejections on a cosmetic defect basis, there are more serious implications to fogging.

The liquid clinging to the glass walls will have dried at a different rate to the solution at the bottom of the vial. It can be questioned whether this might affect quality and reconstitution behaviour in the area of fogging compared to the lyo cake area.

Perhaps most serious of all, severe fogging that reaches the shoulder or neck of the vial may potentially compromise container closure integrity (CCI), which in turn calls into question the sterility of the finished drug product.

How can fogging be prevented?

The most effective solution to prevent or reduce fogging is to use a vial with a smooth, hydrophobic internal coating that will resist product creep, such as SCHOTT’s TopLyo® vial.

Specially designed for freeze drying applications, the TopLyo® vial has a covalently bonded
Si-O-C-H internal surface, which repels liquid and aids the formation of a neat lyo cake.

For even greater protection we recommend the stopper used also features hydrophobic qualities.

West’s FluroTec® Freeze Drying stoppers benefit from an inert and hydrophobic FluroTec® lamination which prevents liquid sticking to the plug area of the stopper.

Vials Lifting in the Freeze Dryer

At the end of the freeze drying cycle the partially inserted stoppers are pressed fully home, typically using a built-in hydraulic stoppering mechanism that compresses the shelves together and enables stoppering of the vials without chamber aeration. On raising the shelves after compression, it is not uncommon for some rubber stoppers to remain temporarily stuck to the shelf, thus lifting the vial, which then drops and may result in breakage.

How do I prevent stoppers sticking to the freeze dryer shelves?

To prevent this happening, pharmaceutical stopper manufacturers have developed stoppers with a
non-stick top surface area.

West’s FluroTec® Freeze Drying stoppers benefit not only from FluroTec® lamination to the product-contact area, but also to the top of the stopper, providing a non-stick ETFE surface which will not adhere to the freeze dryer shelves.

The Wrong Vial Size

It may seem logical to use a 2ml vial for a 2ml liquid fill. And that would be true if your product was intended to remain in liquid form. It is not, however, ideal when the contents are to be freeze dried.

Freeze-drying starts from the top down, and during the process a layer of dried product builds on top of the remaining frozen product. This dried layer presents a resistance to the flow of vapour being sublimed from the product, which becomes greater as the thickness of the dry layer increases.

Increased resistance to vapour flow results in a reduced sublimation rate and a decrease in the cooling effect experienced by the product due to sublimation. Not only does this decrease the efficiency of the drying process, but it may also lead to excess energy input to the product, increasing the temperature and potentially resulting in a collapse of the drying structure.

How do I know which vial size to use?

It is recommended that for freeze drying in the vial, you have a maximum liquid fill depth of 12-15mm. You should use a vial with a large enough diameter to accommodate this.

We are happy to provide you with sample vials of differing diameters for evaluation.

Request a sample.

Commonly Freeze-Dried Products Include

Vaccines and antibodies

Cells and tissues

Viruses and bacteria

Proteins

Enzymes

Sera