LYOPHILIZATION - Lyo 101: Challenges & Solutions in Lyophilization Cycle Development

INTRODUCTION

Commonly known as freeze-drying, lyophilization is a critical unit operation in the pharmaceutical industry utilized to preserve and stabilize small and large molecule drug products and bio­logics, including monoclonal antibodies, vaccines, and peptides. The process involves first freezing a liquid drug product, then re­moving the frozen solvent via sublimation, providing a stable solid matrix of drug product and other excipients. Lyophilization is particularly suitable for heat-sensitive molecules, as it signifi­cantly mitigates hydrolysis degradation found in liquid product, is more product-sensitive and practical than other drying meth­ods, and avoids the difficulties of multi-component powder fill­ing.

Biopharmaceutical companies have increasingly favored lyophilization for pharmaceutical product formulation, primarily due to its ability to stabilize drug products and excipients in a solid matrix to significantly increase shelf-life. Logistics are another fac­tor as removing solvents from a formulation simplifies storage and distribution.

For instance, many lyophilized drug products benefit from increased thermal stability and no longer require frozen storage. The result is a more cost-effective, lower-risk, and efficient way to optimize storage and distribution. This is particularly beneficial for drug products shipped to countries with less-developed infra­structure or tropical climates, where temperature may affect prod­uct stability and cold chain storage may be unavailable.

As companies continue to pioneer new molecules and treat­ments, molecule stability has emerged as a persistent detriment to every iteration. Increasingly, lyophilization is an attractive path to a sustainable, repeatable solution.

As the number of biologic molecules in the drug develop­ment pipeline increases, more products will stand to benefit from lyophilization; in fact, many may not be commercially viable oth­erwise. Per the LyoHub 2023 Annual Report, in the past decade, submissions for lyophilized drug approvals have increased by an average 15% per year. From 2012 to 2022, a total of 336 lyophilized drugs were approved, a figure constituting 59% of the total fillings since 1954. In 2022, the US FDA approved 32 lyophilized drug products, with oncology and infectious disease medications combining to represent 82% of approvals.¹

Of course, a solution as sophisticated as lyophilization comes with its own unique challenges. Its complexities and intricacies make the process as much an art form as a science, with each drug product presenting unique challenges. Designing consistent, high-quality lyophilization cycles demands an understanding of individual chemistry, characteristics, and interaction. While there are myriad techniques to perfect and tools to utilize, the following is a brief guide toward a successful lyophilization process.

THE LYOPHILIZATION CYCLE

Achieving optimal product stability and quality via lyophiliza­tion encompasses a meticulous series of well-executed steps. But while each step has its own intricacies and idiosyncrasies, the overall process can be broadly categorized into three phases: freezing, primary drying, and secondary drying.

Thermal Treatment (Freezing) Phase
The first step in lyophilization is the initial freezing and sub­sequent thermodynamic arrangement of the product. Called ther­mal treatment, this simple yet crucial step ensures full nucleation of the solvent and generates a uniform frozen matrix to prepare the product for the primary drying phase, known as sublimation. Controlled freezing rates, along with annealing and process knowledge of super cooling effects, are often employed to achieve uniform ice crystal distribution. Newer technologies are also providing the ability to nucleate on demand, further increasing product uniformity across lyophilizer shelves and representing a promising enhancement in next-generation lyophilization technology.

At the beginning of the lyophilization process, products must be formulated in a manner suitable for thermal treatment. To safeguard the product during freezing, this step frequently incorporates cryoprotec­tants, such as saccharides and polyols. Cryoprotectants help maintain the prod­uct’s structural integrity by protecting drug substance molecules against drying stresses; in the case of biologics, they also help maintain conformation and prevent agglomeration. Bulking agents may also be added to the formulation to ensure a stable and elegant post-lyophilization cake.

Primary Drying Phase – Sublimation
Following thermal treatment, the most crucial aspect of the lyophilization process begins: Primary drying is the namesake thermodynamic process in freeze-drying and, in turn, the most critical to under­stand. Initially, a vacuum is applied at a very low temperature (the final freeze tem­perature) and set to control; for most processes, this is typically between 30-300 mTorr.

Once the vacuum is controlled, shelf temperature is gradually increased, incre­mentally introducing heat to the frozen product. When the frozen solvent’s vapor pressure surpasses the lyophilizer’s set pressure, sublimation begins.

The temperature and pressure set points during primary drying, along with the times required, are critical to achieving efficient sublimation without compromis­ing product quality. Process analytical tech­nology (PAT) tools, such as Pirani gauge and product temperature monitoring, ther­mal characterization analytics (mDSC, FDM), and technical prowess of analysis (eg, fully comprehending product resistiv­ity, evaporative cooling, and thermal treat­ment impact) are just a few processes that the most capable manufacturers use to strike the delicate balance between drying time and subsequent product quality. The process is strictly monitored while solvent undergoes sublimation and, upon com­pletion, now resembles a successfully lyophilized product.

Secondary Drying Phase – Desorption
Once primary drying is proficiently performed, the process has typically re­moved between 90%-95% of the solvent and produced a physically stable lyophilized matrix. However, one hurdle remains: frequently, manufacturers now confront leftover solvent bound between crystals that cannot be fully removed by sublimation alone.

To address this challenge, this final phase of secondary drying involves further removal of the lyophilized product’s resid­ual moisture. This is accomplished by in­creasing the temperature and removing bound solvent via desorption. Here, tem­perature and drying rates are primarily dictated by stability parameters of the ac­tive pharmaceutical ingredient (API) or bulk drug substance (BDS), meaning care must be taken to prevent degradation of the product. Monitoring residual moisture content is crucial during this phase, and critical to map and understand.

While there are a plethora of other characteristics and intermediary phases that must be analyzed and gauged throughout the process, successful design of the three phases mentioned earlier should yield an acceptably lyophilized product capable of withstanding the stresses, pathways, and timelines to reach the process’ most critical players: health­care personnel and patients.

CRITICAL SUCCESS FACTORS IN LYOPHILIZATION

A well-executed lyophilization cycle can maintain the product’s Critical Quality Attributes (CQAs) throughout its lifecycle, with minimum time and energy consump­tion. The following are some critical ele­ments.

Product Formulation
A product’s composition, including excipients and the selection of cryoprotec­tants and bulking agents, significantly in­fluences lyophilization cycle development and overall efficiency. To ensure quality is maintained, the product formulary must be designed with the lyophilization process in mind, with any formulary changes thor­oughly scrutinized to consider each phase of the lyophilization process.

Drying Chamber Design
The design of the lyophilization cham­ber affects the efficiency of the process. Factors such as internal versus external condensing, shelf temperature uniformity, chamber pressure control, and condenser capacity are critical in achieving consistent, reliable lyophilization cycles. Ideally, chambers are rigorously modeled so that vial-to-vial variability is minimized.

Vacuum Level and Pressure Control
Proper vacuum levels and pressure control during the primary drying phase are essential for efficient sublimation. Careful monitoring and astute, timely ad­justments to these parameters best ensure the removal of water vapor without com­promising the product’s structural integrity.

Temperature Control
Precise temperature control through­out the lyophilization cycle is vital. Both freezing and drying temperatures must be carefully monitored and controlled to pre­vent product collapse, degradation, or for­mation of analogous products.

Monitoring & Control Systems
Two other integral aspects of lyophilization cycle development are ad­vanced monitoring and control systems. Real-time monitoring of critical parame­ters, such as shelf temperature and pres­sure, as well as PATs, such as Pirani gauges, mass spectrophotometers, and state-of-the-art monitoring software, en­sure process consistency and product quality.

LYOPHILIZATION CYCLE DEVELOPMENT PROCESS

Lyophilization cycle development is a meticulous and multifaceted task that re­quires careful consideration of various pa­rameters to ensure product quality, efficacy, and stability. Developing an opti­mal lyophilization cycle involves several steps.

Formulation Design
The product’s formulation must be carefully designed to ensure suitability for lyophilization because its composition – in­cluding buffers, excipients, and selected cryoprotectants – will significantly influence cycle development. The drug product for­mulation therefore must be optimized to ensure product stability and maintain the desired characteristics throughout the freezing and drying process.

Thermal Characterization
Cycle development begins with un­derstanding the Critical Process Parame­ters (CPPs) typically seen in lyophilization, and leveraging that knowledge to ensure a formulation is physically suited to un­dergo lyophilization at the designed CPPs. Thermal characterization utilizes tech­niques, such as Modulated Differential Scanning Calorimetry (mDSC) and Freeze Drug Microscopy (FDM), to establish the product’s critical temperature bench­marks, including the temperatures at which the product undergoes a thermody­namic change in state via glass transition, recrystallization, and eutectic melt. Even a qualitative change of state observed via FDM (collapse onset) is crucial to product characterization. Once established, the focus reverts to the lyophilization cycle pa­rameters, and temperature and vacuum levels are recommended to ensure product quality and prevent failure.

Cycle Design & Optimization
The cycle’s parameters – including freezing rate, shelf temperature, and vac­uum pressure – are determined based on the product’s characteristics and stability requirements. Guided by Quality by De­sign (QbD) principles, cycle design is fine-tuned through a series of experiments to achieve an overall successful design space and range in which the lyophilizer param­eters can operate. Lyophilization cycle pa­rameters are optimized for multiple factors, including a low residual moisture, cake appearance, reconstitution, low degradation and total run time. Optimiz­ing the cycle for total run time can lead to cost efficiencies over the product’s lifecy­cle.

Cycle Validation
The optimum lyophilization cycle is then validated to ensure reproducibility, consistency and robustness. This step is es­sential for scalability and meeting regula­tory standards.

REFERENCE

1. Pharmahub – Resources: LyoHUB 2023 Annual Report: About

Matt Bourassa is a Process Development Group Manager for PCI Pharma Services, a leading global CDMO providing clients with integrated end-to-end drug development, manufacturing and packaging capabilities that increase products’ speed to market and opportunities for commercial success. During his 14 years in the CDMO space, he has developed more than 30 robust and scalable lyophilization cycles across a wide array of parenteral drug products, medical devices, and diagnostics. As an inaugural member of the Process Development team, he now manages highly skilled scientists in the same group, leveraging his process knowledge and technical prowess to inform scientists and clients alike, from small scale preclinical tests to late-stage characterization and aseptic fill-finish. He earned his BS in Chemical Engineering from the University of Massachusetts.