Parenteral Formulation: Deciding When to Go Frozen or Freeze-Dried

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While many parenteral products can be stored and shipped in the liquid state at room temperature, some, including most based on biologic drug substances, must be maintained at low temperatures. When refrigeration is not sufficient, two options remain: keeping the products in a frozen state or freeze-drying (lyophilizing) them into a powdered form. There are advantages and disadvantages to both, with many factors to consider when choosing between the two solutions.

Instability and time drivers

The biggest driver for freezing or freeze-drying parenteral products is instability of the drug substance when in solution. This issue does not often arise for small-molecule APIs, but is common for recombinant proteins and antibody-based molecules. “Developing freeze-dried or frozen parenteral formulations is primarily driven by the inherent instability of biological molecules in solution at or below room temperature, limited shelf life in liquid form, high sensitivity to temperature fluctuations and air-liquid interfaces, and excipient-related limitations,” says Maria Fernanda Zuluaga Estrada, principal scientist and formulation development group leader at Lonza.

Protein molecules, explains Jeremy Guo, senior vice president and head of drug-product development and clinical drug-product manufacturing at WuXi Biologics, are physically and/or chemically unstable during long-term storage, suffering from aggregation and visible particle formation, deamidation, oxidation, and other degradation pathways, even in optimized aqueous formulations after formulation screening.

“Freezing or lyophilizing these formulations is the optimal choice, because physical and/or chemical reactions will be inhibited in the frozen glassy state or freeze-dried state with minimal water content,” Guo says. At Lonza, advanced analytical tools are used for diagnosing vulnerabilities potentially leading to instabilities, including mass spectrometry to detect and foresee post-translational modifications, holistic (i.e., stability-indicating) surfactant analytics, subvisible particle characterization to differentiate potential protein-versus-surfactant instability, in-depth root cause analysis in case of surfactant degradation, in-depth host-cell protein, especially lipase, characterization and quantification, and container-closure integrity testing and qualification.

Beyond instability, time can also be a driver for choosing to freeze or lyophilize a drug candidate. “When the development timeline is very limited for early filing of an investigation new drug (IND) application, the final formulation needs to be locked down without completion of comprehensive formulation screening or generation of sufficient stability data. Freezing or freeze-drying can help ensure long-term stability while still meeting these shorter timelines. Comprehensive screening can then be performed during late-stage development to determine the final, commercial formulation,” Guo observes.

Surfactant degradation also a factor

There is one other significant reason for moving forward frozen or freeze-dried formulations during the development of biologics, according to Zuluaga Estrada. Many liquid biologic formulations have limited expected shelf-lives when stored at or below room temperature due to surfactant degradation, which is why Lonza conducts so many surfactant-related analyses. “For cases where extensive lipolytic activity is demonstrated, Lonza’s proprietary lipase assay can support the removal of lipolytic activity during downstream processing,” she notes. The company also has a proprietary approach to lipase inhibition that involves addition of low concentrations of citrate to mitigate surfactant degradation, which can potentially prevent the need for frozen or lyophilized storage, Zuluaga Estrada adds.

Advantages and disadvantages of frozen formulations

The primary advantage of frozen formulations is their ability to preserve unstable formulations due to the immobilization of molecular components, thereby extending the shelf life, observes Zuluaga Estrada. Development of frozen formulations also generally takes less time and is less expensive than the development of lyophilized products, according to Guo. The lack of the need for a reconstitution step, which is required for freeze-dried formulations, is another benefit noted by Guo.

There are several disadvantages to frozen formulations, however. “The complexity of developing frozen formulations is often not considered in full, and the related challenges present a substantial risk in the development of biologics,” Zuluaga Estrada contends. She highlights lack of molecule or excipient stability in certain frozen formulations (e.g., cold denaturation and aggregation of proteins, crystallization of excipients, phase separation) and compromised integrity of the container-closure system at ultralow temperatures as two examples.

Beyond stability issues, the key challenge with frozen products is the need for extensive infrastructure and shipping capabilities to support the cold chain, says Zuluaga Estrada. “Robust freezing parameters, appropriate storage conditions, and adequate supply chain management need to be considered,” she notes.

Temperature excursions during storage and shipment of frozen products, adds Guo, can lead to ice crystal formation, protein denaturation, and a potential decrease in drug efficacy. In addition, the need for temperature control during storage and shipment at manufacturing sites, depots, and clinical centers adds significant cost and inconvenience, he comments.

Other concerns pointed out by Guo include the higher risk of vial breakage and the need for lower filling volumes compared to liquid drug products in the same container to reduce this risk.

To avoid these issues, often redevelopment to a liquid or lyophilized formulation is pursued once a candidate reaches later development stages and looks to be commercialized. However, switching to a liquid or freeze-dried product during late-phase development requires significant additional effort and adds cost and time for programs, according to Zuluaga Estrada.

Lyophilized formulations present opportunities and challenges

Freeze drying also has both positive and negative attributes. In addition to overcoming formulation instability issues, one of the biggest benefits is the ability to store and ship products at refrigerated (2–8 °C) or even room temperatures, Guo says.

Appropriate storage of lyophilized cakes within these temperature conditions (i.e., below their glass-transition temperatures), significantly reduces the logistical and storage constraints compared to frozen products, agrees Zuluaga Estrada. “That translates to greater storage and transport efficiency, particularly for global products and patient-centric delivery,” Guo concludes.

As with frozen formulations, however, it is necessary to use lower filling volumes than those of liquid products in the same container to ensure efficiency of the lyophilization process. In addition, Guo observes that the development of freeze-drying processes requires specialized expertise and capabilities and often adds time. The lyophilization process is also energy-intensive and extends the overall manufacturing time.

The need for reconstitution before administration also poses some concerns. Not only does Guo note the potential risk of product contamination by stopper debris after multiple punctures for reconstitution and sampling, high-concentration formulations can be challenging with respect to the time required and the potential for dosing errors and introduction of contaminants.

Despite the complexity, expense, and extended timelines typically associated with the development of lyophilized products, with the right expertise and robust platform cycles, it is possible to develop freeze-dried formulations in similar timeframes compared to liquid formats, according to Zuluaga Estrada. “We employ specialized characterization techniques including modulated differential scanning calorimetry (mDSC) and freeze-drying microscopy (FDM) to identify key thermal changes and, as required, optimize and develop robust lyophilization cycles in cost-effective timelines and with low material requirements,” she explains.

Primary factors to consider

Given the different advantages and disadvantages of freezing and freeze-drying of parenteral formulations, there are some general factors that often influence the choice of one method over another. First is the ability of the drug substance to withstand the lyophilization process and/or freeze-thaw cycles, according to Zuluaga Estrada. The clinical application and route of administration are also important considerations. For instance, she notes that the acceptance of lyophilized formats is lower for emergency medications that must be administered immediately and medicines given via intravitreal administration. Other aspects that should be taken into account include the development phase, supply chain, timelines, and costs.

In general, says Guo, frozen products are often preferred if the development timeline is severely limited (e.g., six months to IND); the product is unstable and sensitive to the freeze-drying process; and the medicine will only require distribution locally or to clinical centers with sufficient cold-chain infrastructure. In addition, he notes that long-term storage at -20 °C is preferred over storage at ultra-low temperatures due to the greater availability of this capability at clinical centers.

Lyophilization is typically preferred, Guo continues, for unstable products that can withstand the freeze-drying process, there is sufficient time for development of an optimal lyophilization process, a long shelf-life is needed, and/or the product will be distributed to globally, including areas where cold-chain management would pose challenges.

“Overall,” Guo concludes, “when selecting between frozen and freeze-dried formulations, scientific, economic, and practical factors should be considered. Stability of the molecule for long-term storage is the primary concern. Other factors such as timeline, costs, storage availability, and distribution logistics should be evaluated as well.”

The evaluation of lyophilized formats can be a backup option for proteins that are unstable in solution at room temperature or under refrigeration or for cases where considerable surfactant degradation (potentially leading to particle formation) is observed, Zuluaga Estrada says.

When lyophilization does not improve protein stability or a lyophilized format is not suitable, such as when large fill volumes or long reconstitution times are involved, frozen storage of the liquid at sub-zero temperatures should be assessed.

About the author

Cynthia A. Challener, PhD, is a contributing editor to Pharmaceutical Technology®.

Article details

Pharmaceutical Technology®
Vol. 49, No. 4
May 2025
Pages: 16-19

Citation

When referring to this article, please cite it as Challener, C.A. Parenteral Formulation: Deciding When to Go Frozen or Freeze-Dried. Pharmaceutical Technology 2025 49 (4).