Lyophilisation: meeting new demand and challenges

Armin Dalluege, General Manager of Wasserburger Arzneimittelwerk, a subsidiary of Recipharm, in Wasserburg, Germany, highlights trends in drug lyophilisation

Lyophilisation (or freeze-drying) in the pharmaceutical field has seen steady expansion combined with on-going development. Demand for lyophilisation within the pharmaceutical and biopharmaceutical sectors is expected to increase in the coming years, with a projected compound annual growth rate (CAGR) of 10.4% through to 2018 and the generation of composite revenues of US$28.7bn by this time (up from $17.6bn in 2013). This is in part fuelled by the multiple benefits that lyophilisation brings to a range of pharmaceutical products, including increased shelf life, preservation of potency and protection from degradation.

The forecast growth will mean greater need for lyophilisation equipment and capabilities, together with specialist knowledge and established experience. CDMOs must address this, in part through an extension of their current facilities or through modifications made to current equipment. Forward-looking CDMOs have responded to this demand by investing in high grade technology and facilities geared towards meeting the growth predicted for the future.

In the case of Recipharm, which has 40 years’ experience in producing drug-filled vials and ampoules, significant investments include b32m spent on lyophilisation capabilities at its Wasserburg site in Germany, expanding capacity with new production facilities, equipment and, crucially, large-scale freeze-drying capabilities.

The many applications of lyophilisation that are driving the demand for more specialist skills, knowledge, capabilities and advanced equipment include significantly improving the dissolution of poorly soluble compounds, increasing a product’s shelf life and enabling storage at ambient temperatures.

For instance, where the characteristics of a liquid product deteriorate out of specification within a few months of storage, freeze-drying can readily extend this to a period of two years. Furthermore, changing the storage temperature of a pharmaceutical product from 2–8°C to room temperature avoids the complications of cold chain supply management, including transportation of the products, and increases patient compliance.

Lyophilisation is critically important for biologics as acceptable stability is only possible as freeze-dried formulations

Freeze-drying or lyophilisation is very well suited to a range of small and large molecules and throughout the pharmaceutical sector many types of drugs are freeze-dried. For example, in the case of lipophilic small molecules, lyophilisation significantly accelerates dissolution due to an increased surface area of the dispersed drug in the porous cake, thus resulting in improved bioavailability. Moreover, lyophilisation is critically important for biologics as acceptable stability is only possible as freeze-dried formulations. This is the situation with many biological compounds, including larger peptides, proteins and antibodies.

Microsphere and Liposomal formulations both lend themselves well to freeze-drying. Microsphere formulations that are used for the controlled release of actives are usually freeze-dried because the formation of a dry state is the only reliable way of preventing premature release of the active before it is administered. Additionally, the API that is encapsulated in the microspheres may also have stability issues that require lyophilisation. Liposomal formulations are very often candidates for freeze-drying because it is the only way of ensuring that their physical shape is maintained, which is essential. Indeed, Lipoplexes – liposomes with additional compounds or groups attached to them – are especially vulnerable.

Leakage of the active from the inner core aggregation or lipid oxidation are all potential threats to biological activity. As a consequence, it is imperative that these formulations are freeze-dried to preserve their initial characteristics. Equally, it is absolutely essential that the correct excipients are selected and optimised due to the fact that freeze-drying is a water-based process.

Market trends

Freeze-drying is increasingly being used in both formulation development and the manufacturing of pharmaceuticals for poorly soluble compounds, biopharmaceutical molecules and biosimilars.

High throughput screening finds promising compounds without consideration of their solubility and the challenges of low soluble compounds become apparent only after a compound has already progressed through its initial development stages

Poor solubility has become a common characteristic of new pharmaceuticals. This is primarily because high throughput screening finds promising compounds without consideration of their solubility and the challenges of low soluble compounds become apparent only after a compound has already progressed through its initial development stages. The application of cosolvents is one possible solution. However, due to the fact that cosolvents can present additional formulation challenges, freeze-drying using organic solvents such as TBA (Tert-butyl alcohol) or TBA-water mixtures is becoming more common.

A further trend is the growth in the number of antibody-based and siRNA-based formulations. These compounds frequently require freeze-drying to maintain the integrity of the formulation or vehicle to target the siRNA in the body.

Complex considerations

There is a range of complex considerations that have to be taken into account when planning and preparing freeze-drying operations. These include the following:

Excipient selection – When developing the formulation, it is essential to take into account the fact that additional excipients will be required to enable lyophilisation of an API in the first place and specifically to protect compounds during freeze-drying. A large number of oligomer polyols, polymers and sugars are used for this.

To determine the precise excipient to be used, specific information, such as physical properties, the flexibility of the backbone of the polymer, the glass transition temperature during freeze-drying and the ability of protectants to incorporate the active, all require consideration.

Furthermore, the selection of pH, antioxidants and/or surfactants can greatly improve the formulation’s performance. The correct selection is of the utmost importance as any excess excipients can have a negative influence on the final pharmaceutical product.

Reconstitution time – Dissolution is accelerated by increasing the specific surface area of the cake. Moreover, maintaining sufficient wettability, especially when incorporating lipophilic molecules, is highly beneficial in this context.

API stability – A number of compounds, including proteins, require protection with special cryo- and lyo-protectants throughout the freeze-drying cycle. There are many protectants that can potentially be used, but not all are suitable; for example, sucrose can be a good cryoprotectant, but it excludes all diabetic patients from the pharmaceutical’s target population.

Formulation stability – The product will need to be stable during the preparation of the formulation, the filling and the freeze-drying process itself. If stability issues emerge during freeze-drying, or before it commences, then the formulation concerned is not optimised for freeze-drying and complicated scientific work in the laboratory will have to start from scratch.

Complex formulations, including lipoplexes, are prone to degradation. Consequently, a protectant with a high glass transition temperature (Tg) is essential for such formulations because the solid matrix must stay amorphous during freeze-drying.

API physicochemical properties – An excipient’s physicochemical properties, together with information regarding a compound’s characteristics, including disintegration properties and solubility profiles, also require important consideration. For example, a protein can affect an excipient’s Tg very differently. The effect of buffer salts and the Tg of the freeze-concentrated fraction is investigated utilising a Temperature Modulated Differential Scanning Calorimeter (TMDSC). This enables a proper starting point for the selection of the product temperature during primary drying.

The site of Wasserburger Arzneimittelwerk, a subsidiary of Recipharm

Freezing rate – The actual freezing of the formulation is the most critical step in a freeze-drying process. The freezing rate at the start of a freeze-drying run is critical to phase separation and concentration gradients in the vial because it can yield more dense layers at the top of the cake, forming a barrier for water transport. Furthermore, it is well known that freezing rates are crucially important for the API to be properly incorporated in the cake. In the early feasibility stage, small freeze-dryers are used and freezing is sometimes achieved simply with liquid nitrogen.

The scalability of such a method and its freeze-drying rate is complicated to translate into a production environment in which industrial scale freeze-dryers are used. It is especially helpful if the freeze-drying process is first developed on a laboratory scale using test runs that mimic a feasible situation in the GMP environment.

A range of freezing rates can be accurately copied and controlled in laboratories using suitable freeze-dryers. Furthermore, the number of vials in a freeze-dryer often have a significant impact on the cooling capacity of the shelves.

Clinical usage – To carry out lyophilisation successfully, clinical staff need to accurately determine critical questions, including: what dose per vial is to be administered and what is the best and most appropriate route of administration? They also have to ascertain what the reconstitution volume and the resulting ionic strength is. Furthermore, during clinical development, dose range finding studies will often complicate vial content decisions. In addition, high dose products present a freeze-drying challenge inasmuch as the formulation leaves very limited room for freeze-drying agents. In this context, it is the concentration in which an API needs to be administered rather than the API itself that presents the challenge.

Water content levels – Essentially, lower water content reduces molecular mobility and consequently increases shelf life. It is therefore important that the correct low levels of water content are achieved.

Freeze-drying economics – This is another complicated and challenging area that pharmaceutical companies have to wrestle with. The freeze-drying cycle time is of key importance. Cake height is reduced and primary drying is shortened by minimising the volume of solution per vial. A shorter freeze-drying cycle is essential to minimise the cost of goods. Secondly, when it comes to scaling up during later clinical development phases, it is beneficial to use a higher concentration of the formulation because you can use smaller vials and, therefore, freeze-dry more vials in a single batch.

Growth outlook

Innovative freeze-drying formulations and freeze-drying techniques qualify for patenting. Consequently, freeze-drying is set to carry on forming an ever more important part of a company’s intellectual property in the future. Therefore, the continuous growth in demand for freeze-dried formulations will also be fuelled by the fact that many of the compounds currently in development are biologics. Such biological products are invariably complicated chemical molecules requiring complex vehicles to enable targeting in the body.

Spray freeze-drying is a fast emerging lyophilisation technique in which liquids are nebulised and then frozen

Spray freeze-drying is a fast emerging lyophilisation technique in which liquids are nebulised and then frozen. These frozen spheres are then freeze-dried. The fast freezing generates instantaneous vitrification and this is highly beneficial for optimal dispersion and stabilisation of the API throughout the solid matrix of excipients. This technique can be performed at atmospheric conditions. It has manufacturing advantages because it allows for continuous operation and increases robustness due to the absence of vacuum. CDMOs, such as Recipharm, have taken the initiative to invest in the specialist equipment to make this innovative technique readily available to customers on the market.

As illustrated, lyophilisation is a highly advantageous and beneficial technique available to the pharmaceutical and biopharmaceutical markets. It is a very complex process and presents multiple challenges to manufacturers operating in the sector. However, all the challenges can be met and overcome if the essential tools are put in place – tools that range from capacity, facilities, capabilities, state-of-the-art technology and skilled and experienced personnel.

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