Thawing a frozen drug substance or active pharmaceutical ingredients can be as simple as taking a bag out of the freezer and waiting. But is the simplest method also the best one?
For sensitive and high-value biologics, thawing is about more than process time. Temperature conditions, thawing rate and product homogeneity can all affect the consistency of the freeze-thaw process and product quality in the end.
There is a business case, too. In one ADC manufacturing case, switching from ambient to controlled thawing resulted in a projected payback of less than one year. What drove the return on investment? We take a closer look below.
This article compares controlled and uncontrolled drug substance thawing, the equipment available in drug substance management, their impact on protein stability and formulation development, and the key considerations when choosing the right thawing method.
Why is drug substance thawing important?
Freezing drug substances can support long-term storage and transport between manufacturing steps. However, returning a frozen drug substance to its liquid state is not simply a matter of letting it thaw. The conditions during freezing and thawing can influence product homogeneity and stability and therefore need to be considered when developing the overall safe handling of bulk drug substances.
During freezing, components of a formulation may become unevenly distributed as ice forms. This can create local differences in protein, salt and excipient concentrations as well as pH. Depending on the molecule and formulation, these conditions can contribute to protein denaturation, aggregation, oxidation and other changes that may affect product quality.
The impact of freeze-thaw conditions is product-specific. Monoclonal antibodies (mAbs), therapeutic proteins, peptides and vaccines can respond differently to the stresses associated with freezing and thawing. Freeze-thaw parameters should therefore be evaluated during process development, using appropriate stability studies and scale-down models when transferring the process to larger volumes.
Uncontrolled thawing in biopharma processes
Drug substances can be thawed using either uncontrolled or controlled processes. Uncontrolled thawing is the simpler approach and requires little or no dedicated equipment. However, thawing conditions are less standardized because heat transfer and thawing rates depend on factors such as ambient temperature, container format and product volume.
Controlled thawing, by comparison, uses defined process conditions and dedicated equipment to manage heat transfer and temperature changes more reproducibly. The differences between the two approaches become particularly relevant when process consistency, monitoring and product stability are important.
What is an uncontrolled thawing process?
In its simplest form, uncontrolled thawing means moving a frozen drug substance into a warmer environment and allowing it to thaw passively, for example by transferring it from cold storage to an ambient manufacturing area.
The advantage of ambient passive thawing is simplicity: no dedicated thawing equipment is required. The trade-off is limited process control. Thawing conditions can vary with ambient temperature and product volume, while the thawing rate itself is not actively controlled.
During thawing, the product passes through a partially frozen state before liquid homogeneity is restored. In this phase, local differences in concentration and other physicochemical conditions can expose the drug substance to stresses associated with aggregation, degradation, precipitation or conformational changes. The actual impact depends on the molecule, formulation and process conditions. To alleviate these issues chemical cryoprotectants are routinely added to formulations, but optimal results are only achievable with faster, properly controlled thawing rates.[[1]]
Heating devices or a waterbath may accelerate passive thawing, but uncontrolled heat input can create local temperature differences or overheating, i. e. undesirable temperatures, leading to degradation and possible contamination with leachables from sub-par bags.[[1]] This makes simply applying more heat an unsuitable substitute for a defined and controlled thawing process.
Pros and Cons of uncontrolled thawing
Uncontrolled thawing has its merits in bioprocesses but there are several downsides as well:
Pros
- Can be a simple move from the cold room to the plant floor
- Not capital intensive, requires no infrastructure
- Heating devices can improve process times and quality
Cons
- Undefined thawing rate
- Takes a longer time, could become a bottleneck in manufacturing processes
- Exposure to wrong pH values, salt concentrations, excessive drug concentration, leading to aggregation, precipitation, degradation, etc.
- Heating devices may cause local superheating
Controlled thawing of drug substances
Controlled thawing uses defined process conditions to bring frozen drug substance back to a liquid state while managing the rate of heat transfer and product temperature. Depending on the process and equipment, temperature can be monitored and adjusted according to predefined parameters, making the thawing process more reproducible than passive ambient thawing.
Pharmaceutical science studies reveal that most aqueous biomolecular drugs benefit from fast freezing and fast thawing to minimize exposure to the critical temperature range from -160 to -15 °C, where ice crystals show the tendency to grow instead of nucleation of new small crystals.
Thawing conditions can be particularly relevant for protein-based biologics. During freezing, ice formation can create locally concentrated regions of proteins, salts and excipients. The subsequent thawing process influences how long the product remains exposed to these non-uniform conditions before returning to a homogeneous liquid state. The appropriate thawing profile therefore needs to be established for the specific molecule, formulation, container and process scale.
