Abstract
The development of biologics, like monoclonal antibodies (mAbs), Antibody-drug conjugates (ADCs) and bispecific antibodies, has provided treatment for diseases once deemed untreatable, such as advanced cancers and autoimmune disorders. As powerful as these biologics are, their development still come with substantial technical challenges.
Behind every biologic drug is a formulation that ensures the molecule’s stability, safety and efficacy. This unassuming yet critical component must handle the inherent complexity of biologics and their sensitivity to environmental factors like pH and temperature, while maintaining efficacy and manufacturability at scale. Increasingly, formulation efforts also address a key patient-centric need: transitioning therapies from intravenous (IV) to subcutaneous (SC) formats. High-concentration formulations are central to SC delivery, but they introduce new technical hurdles that demand a great deal of expertise.
Challenges in biologic drug formulation
Physicochemical complexities
Biologics are inherently sensitive to their environment due to their large, complex molecular structures. Changes in temperature, pH and mechanical agitation can destabilize these molecules, leading to aggregation, degradation or precipitation. These issues can cause irreversible damage to the product with a subsequent loss of therapeutic efficacy or inducing adverse effects in patients.
Aggregation remains one of the most common challenges in biologic formulation. Aggregation not only reduces the potency of the biologic but also poses a significant risk of triggering adverse immune reactions. These aggregates often form due to weak intermolecular forces that become pronounced during storage or under stress conditions such as agitation during transport or freeze-thaw cycles.
Another issue is viscosity. At higher concentrations – often required for SC delivery – viscosity can increase exponentially with protein concentration. This elevated viscosity presents challenges for drug delivery, as it can exceed the capabilities of standard SC injection devices like autoinjectors. In addition, this impact on injectability can be complicated by the non-Newtonian behavior demonstrated by biologics at high concentrations.
High-concentration formulations
The growing need for high-concentration biologics stems from patient-centric demands for SC delivery, which offers greater convenience compared to IV administration – patients can self-administer in the comfort of their own homes, and do not require a hospital bed and medical staff to receive their treatment.High-concentration formulations allow for smaller injection volumes, but this comes with its own technical challenges.
At higher concentrations, biologics often exhibit increased viscosity due to protein-protein interactions. These interactions make injection difficult and can also contribute to instability, leading to aggregation, precipitation or gelation during storage. Such behaviors are particularly pronounced in ADCs and multispecific antibodies, where different structural domains may interact unfavorably under the same formulation conditions. For instance, stabilizing a monoclonal antibody (mAb) could compromise the chemical stability of its linker-payload system if done incorrectly.
High concentrations also exacerbate opalescence and particle formation, which need to be addressed to meet regulatory requirements. The challenge is not only in identifying these issues but also in resolving them without compromising the biologic’s safety, efficacy or manufacturability. Advanced analytics and innovative approaches are essential to overcome these hurdles.
Manufacturing and scalability
Once a biologic formulation is optimized, scaling up to commercial manufacturing presents another set of challenges. High-concentration formulations must retain their stability and consistency across large-scale production batches. Aggregation, viscosity, and phase separation tendencies can intensify during manufacturing processes such as mixing, filtration, and filling.
Moreover, these formulations often require highly specialized equipment and expertise. SC biologics, for example, must be compatible with autoinjector devices, which necessitate tight control over viscosity and injectability. Regulatory demands for stability testing, shelf-life validation and cold chain logistics add further complexity, particularly for global distribution.
Overcoming these challenges
Advanced analytical tools
Advanced analytics underpin successful formulation development. Techniques such as size exclusion chromatography (SEC), differential light scattering (DLS), and imaged capillary isoelectric focusing (icIEF) can be used to help understand and resolve stability issues. These methods allow researchers to monitor aggregation, viscosity and protein behavior under stress conditions, giving them the ability to fine-tune formulations to meet clinical and regulatory requirements.
Delivery systems
New delivery systems, such as lipid nanoparticles (LNPs) and polymer-lipid hybrids, are proving popular for biologics. LNPs protect sensitive biologics from degradation and enhance solubility while offering controlled release profiles. Polymer-lipid hybrids offer a balance of stability and biocompatibility, allowing targeted delivery and improved drug performance.
Overcoming viscosity challenges
Excipient screening plays a major role in reducing viscosity while maintaining protein stability. For example, viscosity-reducing agents must be carefully studied to avoid destabilizing intermolecular interactions critical for maintaining biologic integrity. A systematic approach to excipient selection ensures injectability without compromising long-term stability.
Case studies
Managing high viscosity for subcutaneous injection
A customer had developed a mAb formulation that performed well in Phase I clinical trials but needed to transition from IV to SC administration for subsequent clinical studies and commercialization. The target concentration was 150 mg/mL, which, while being stable, significantly exceeded the viscosity limit for SC injection devices (20 cP). At this concentration, the formulation exhibited a viscosity of 34 cP, making it unsuitable for use with standard SC delivery devices.
To address this, the formulation team undertook a screening process to identify viscosity-reducing excipients. Several buffers were tested to determine their impact on viscosity without compromising stability. This process revealed an excipient that reduced viscosity to within the acceptable range for SC injection while maintaining the biologic’s stability.
Stress testing confirmed that the selected excipient did not introduce instability. In fact, it marginally improved the protein’s resistance to aggregation under accelerated conditions. The reformulated product successfully met all requirements for SC delivery and progressed to clinical studies.
Improving solubility and stability
Another customer presented a novel mAb that had been developed at a different CDMO. The formulation exhibited phase separation and gelation during refrigerated storage, which resolved upon warming to room temperature. While this behavior did not immediately affect the biologic’s quality, it posed significant regulatory challenges and raised concerns about usability in clinical and commercial settings. This problem came from the fact that the fundamental properties of the mAb had not been assessed during pre-formulation.
The formulation team designed a study to investigate the underlying causes of these issues. They evaluated critical factors such as pH, ionic strength and excipient compatibility. Through this analysis, the team identified that the original formulation’s ionic environment was unsuitable for the mAb’s physicochemical properties. Adjustments to the buffer system improved solubility and eliminated the phase separation issue.
The optimized formulation demonstrated long-term stability, remaining clear and free of visible particles after six months of storage at 2–8°C. Additionally, the reformulation allowed the biologic’s concentration to increase from 50 mg/mL to 100 mg/mL, meeting the customer’s clinical requirements.
Trends driving the future of biologic formulation
High-concentration biologics for subcutaneous delivery
The shift toward high-concentration biologics reflects the increasing need for therapies that align with patient convenience and clinical practicality. SC administration reduces the need for prolonged clinical visits, but creating formulations capable of delivering high-dose biologics in low injection volumes requires solving significant technical hurdles.
Newer biologics, such as ADCs and multispecific antibodies, complicate this further . Their structural complexity and functional diversity demand tailored formulations. For ADCs, the payload’s stability must be balanced with the antibody’s integrity, while multispecific antibodies require conditions that stabilize multiple binding domains simultaneously. These developments are reshaping how formulation scientists approach high-concentration challenges, driving new developments in excipients, analytical tools and delivery devices.
AI and machine learning in formulation
AI and machine learning are enabling faster, data-driven decisions. These technologies are especially valuable in predicting complex interactions between biologics and excipients, which are often difficult to determine experimentally. By analyzing historical data and modelling molecular behavior, AI can identify potential aggregation hot spots, viscosity risks or stability concerns before these issues arise in the lab.
Incorporating AI alongside traditional ‘wet lab’ work during pre-formulation can also reduce the number of experimental iterations required, speeding up the development cycle. Beyond early formulation, machine learning algorithms are being applied to refine scale-up processes and predict long-term stability, helping to meet both clinical and regulatory demands with greater efficiency.
Advanced delivery systems
The growing role of personalized medicine in healthcare is pushing biologic formulation toward greater flexibility. Many emerging therapies – such as gene therapies and targeted oncology treatments – require delivery systems that can handle sensitive payloads while providing precise targeting. LNPs are leading this change as they offer protection and controlled delivery for biologics like mRNA and peptides.
Future progress in this area will hinge on optimizing LNP formulations for specific therapeutic needs. This includes fine-tuning particle size, charge and release profiles to match the molecular characteristics of the biologic and the target tissue. Advances in polymer-lipid hybrid systems also suggest opportunities for sustained release formulations, which could improve the efficacy of biologics requiring steady, prolonged exposure.
Sustainability and accessibility
Sustainability is an important consideration in biologic formulation. As cold chain logistics dominate biologic distribution, there is a need to create formulations that are stable across broader temperature ranges. Lyophilization and excipient systems designed to enhance temperature stability are already being explored to mitigate dependence on energy-intensive cold chains.
Additionally, there is an industry-wide push to reduce the environmental footprint of biologic manufacturing. Continuous manufacturing processes, which minimize waste and resource use, are slowly being adopted as a more sustainable alternative to traditional batch production. These advances not only reduce environmental impact but also make biologics more accessible to patients in regions with limited infrastructure.
Why CDMOs are integral to success
Biologic formulation requires deep scientific and technical expertise. CDMOs with integrated capabilities and advanced facilities can meet demands of biologic development. From overcoming viscosity challenges to ensuring manufacturability at scale, these partnerships help ensure therapies reach patients efficiently and effectively.
Formulation is the lynchpin of biologic success that ensures efficacy, safety and accessibility. Addressing the complexities of high-concentration biologics demands innovative strategies and collaboration across disciplines. By partnering with CDMOs, scientists can reach the full potential of their biologics with the goal of moving transformative therapies for patients forward.
