High-concentration biologics require coordinated formulation and device development to support practical subcutaneous administration.
Viscosity can affect biologic stability, manufacturability, injection force, device compatibility, and administration experience.
Subcutaneous delivery strategies must balance concentration, injection volume, administration time, and patient comfort.
Device selection for biologics should begin earlier in development, especially for high-dose or large-volume products.
Successful biologic drug delivery depends on aligning formulation design, manufacturing requirements, patient needs, and the intended administration setting.
When Biologic Delivery Becomes a Product Design Challenge
The movement of biologics from intravenous (IV) infusion toward subcutaneous (SC) administration has changed the development problem. For many products, the question is no longer only whether a molecule can be formulated at a clinically useful dose. It is whether that dose can be delivered in a form that is stable, manufacturable, compatible with the intended device, acceptable to patients, and practical within the administration setting.
That challenge becomes especially clear for high-dose biologics. SC delivery has traditionally been limited to fluid volumes of 1–2 mL, with more recent increases to about 3 mL.1 Those limits matter because many biologics require substantial doses. When a required dose cannot be delivered within a small volume at conventional concentrations, developers may need to increase the concentration of the product, increase the delivered volume, or pursue some combination of both strategies. Each path introduces tradeoffs. Higher concentrations can increase viscosity, and high viscosity can affect stability, manufacturability, and delivery or administration.1 Larger volumes can change the administration time, the delivery system, the care setting, and the patient experience.
The result is a broader design problem than the phrase “high-concentration formulation” might suggest. Concentration is one lever, but not the only one. Viscosity, injection force, device format, needle configuration, injection speed, injection volume, formulation composition, and patient training can all influence whether a biologic is suitable for SC use. Some of those factors begin in formulation development, while others become most visible at the point of administration. However, they cannot be treated as fully separate development questions, because the same decision can affect multiple parts of the product profile.
This is why the device challenge is inseparable from the formulation challenge. Technologies used for high-dose or high-volume SC delivery may aim to enable high-concentration injectables greater than 100 mg/mL for antibody products, facilitate delivery of fluid volumes greater than 3 mL, or modify the SC space to make larger-volume delivery feasible.1 Those approaches are not interchangeable. A highly concentrated formulation delivered through a prefilled syringe presents a different problem than a larger-volume product administered through a wearable injector or a healthcare professional–administered delivery system. The best approach depends on dose, viscosity, product stability, intended patient population, administration setting, and the tolerance of the product and device for real-world use.
For developers and contract development and manufacturing organizations (CDMOs), the practical implication is that formulation, device, and patient experience questions need to converge earlier. A formulation that is stable in a vial may still be difficult to inject. A device that can deliver a larger volume may still require administration times or use conditions that are not ideal for the target population. A viscosity-reducing strategy may improve injectability but introduce new stability considerations. A product intended for self-administration may face different constraints than one administered by a healthcare professional. High-concentration biologics therefore require a development model that can evaluate the product as a formulation, a manufacturing process, a delivery system, and a patient-facing therapy at the same time.
Viscosity as a Formulation, Manufacturing, and Delivery Constraint
Viscosity is often discussed as a formulation property, but for high-concentration biologics, it functions as a cross-functional constraint. It can influence how a product behaves during development, how it can be manufactured and filled, how it moves through a device, and how it feels during administration. That makes viscosity both a technical attribute and a practical determinant of product viability.
High-concentration formulation development can involve several liabilities, including protein aggregation, precipitation, opalescence, particle formation, and high viscosity.2 These risks are connected because they emerge from the behavior of proteins in concentrated solution. As concentration rises, protein–protein interactions can become more pronounced, and the formulation may become harder to stabilize, characterize, process, and administer. A product may meet the dose target but still present unacceptable risk if concentration creates instability or viscosity that cannot be managed within the intended product configuration.
For monoclonal antibody (mAb) products, the pressure to increase concentration is often tied to the goal of SC administration. The transition from IV infusion to SC delivery can require high-concentration formulations, defined in one review as injectable mAb products with overall concentrations of 100–200 mg/mL.3 That concentration range is clinically attractive because it may allow a therapeutically meaningful dose to be delivered in a smaller volume. At the same time, increasing mAb concentration can introduce biophysical instability and increased viscosity, which are central hurdles for high-concentration mAb products.3
The development challenge is not simply to reduce viscosity as much as possible. A lower-viscosity formulation must still maintain product stability, manufacturability, and quality. Salts and amino acids have been reported as excipients that can reduce viscosity at a given antibody concentration, but viscosity-lowering excipients can also affect protein stability.3 That tension makes formulation selection a balancing exercise. A strategy that improves one attribute can create risk elsewhere, and the best formulation is not necessarily the one that optimizes a single variable.
This is where early developability work becomes important. New experimental, low-mass, high-throughput, and in silico approaches have emerged to help predict high-concentration formulation liabilities.2 These tools are valuable because high-concentration development can be material-intensive, and late-stage discovery of viscosity, aggregation, or other formulation liabilities can force costly reformulation or device reassessment. Earlier screening gives developers a better chance to identify molecules and formulation conditions that are more compatible with the intended route of administration.
The device connection begins with the same property. Viscosity affects the force required to move a formulation through a delivery system, the time required for administration, and the device options available for a given product. A formulation that is acceptable for one route or device may not be practical for another. A viscosity profile that is manageable in a healthcare setting may be less suitable for patient self-administration. A product that can be delivered slowly by a device may still need to meet expectations around convenience, comfort, and confidence.
Because of that, viscosity should not be treated as a late-stage device problem. By the time a formulation is handed off for device selection, the concentration, excipient system, stability profile, and intended dose volume may already limit the realistic delivery options. A more integrated approach begins by asking what concentration and viscosity range can support the target dose, administration route, device format, and patient experience. That does not mean device requirements should dictate formulation choices in isolation. It means that formulation design should account for how the product will actually be administered.
Where the Device Challenge Begins
The device challenge begins when formulation properties meet the physical realities of injection. For high-concentration biologics, this happens earlier than many development programs would prefer. A product may look promising from a dose and stability standpoint but become difficult to administer if viscosity, volume, or flow requirements exceed what is practical for the selected delivery format. Conversely, a device may appear suitable in concept but prove mismatched to the final formulation or the intended use setting.
SC delivery technologies can address high-dose biologic delivery in different ways. Some approaches support high-concentration injectables, some enable larger fluid volumes, and some aim to make the SC space more permissive for larger-volume delivery.1 That range of options is useful, but it also complicates development. Each device or delivery strategy brings its own assumptions about injection time, use setting, user training, fill volume, tolerability, and product-device compatibility.
For small-volume SC products, the device decision may center on familiar formats, such as prefilled syringes or autoinjectors. As dose volume increases, the administration strategy can shift toward longer injections, healthcare professional administration, or devices designed to deliver larger volumes over longer durations. That transition changes the meaning of convenience. A few seconds of manual injection, a brief autoinjector use step, and an extended wearable delivery event are all SC administration, but they are very different experiences for patients, caregivers, and healthcare systems.
Injection force is part of this broader design space. High-viscosity formulations can require more force to move through a needle or device, and force requirements can affect whether a product is suitable for manual injection or whether mechanical assistance is needed. The approved source set supports the importance of evaluating viscosity, injection volume, and injection flow rate as variables that influence SC injection tolerance.4 It does not support a simplistic rule that viscosity alone determines acceptability. That distinction matters because the development question is not whether viscosity is “good” or “bad,” but whether the full product-device configuration can deliver the dose reliably, comfortably, and consistently.
The same caution applies to administration time. Longer delivery may make it possible to administer larger volumes or more viscous formulations, but time is not only a technical parameter. It affects patient preference, clinic workflow, caregiver burden, and the practicality of at-home administration. A product intended for chronic self-administration may face a different threshold for acceptable administration time than a product administered by healthcare professionals during oncology treatment. Those differences should influence device strategy before the product reaches late-stage development.
Device selection therefore requires a more nuanced view of formulation performance. Developers need to know not only whether a product can be formulated at the target concentration but also how it behaves under the conditions of administration. That includes its viscosity at the relevant concentration, its compatibility with the delivery system, the force or flow requirements needed to administer it, and the resulting experience for the intended user. The device is the last interface in the development chain, but it should not be the last consideration.
Injection Volume, Flow Rate, and the Limits of Simple Assumptions
SC injection tolerability is often discussed in terms of volume and viscosity, but the relationship between formulation properties and patient experience is not always intuitive. A study evaluating viscosity, injection volume, and injection flow rate examined how different combinations of those variables affected SC injection tolerance in healthy subjects.4 In that study, high-viscosity injections were shown to be the most tolerated, while injection volume and flow rate did not affect perceived pain. The results also suggested that solutions up to 3 mL and up to 15–20 cP injected into the abdomen within 10 seconds were well tolerated without pain.
That finding is important because it challenges overly simple development assumptions. It would be convenient to conclude that lower viscosity always means better tolerability, or that larger volumes are always less tolerable, or that faster injections always create more pain. The available evidence does not support that kind of universal rule. Instead, viscosity, volume, injection site, flow rate, formulation composition, and patient characteristics all need to be evaluated in context.
For high-concentration biologics, this creates both opportunity and caution. The opportunity is that formulations with higher viscosity may still be feasible under the right conditions. The caution is that tolerability data from one product, injection site, volume range, device, or study population cannot be automatically generalized to every high-concentration biologic. A product administered into the abdomen within a controlled study is not necessarily the same as a chronic therapy used at home, a product administered into another injection site, or a larger-volume biologic delivered over a longer period.
Injection volume also has to be considered through the lens of product category and administration setting. A systematic review of large-volume SC biopharmaceuticals identified 182 large-volume SC products, predominantly monoclonal or bispecific antibodies, corresponding to approximately 15% of all IV and SC biopharmaceuticals reviewed.5 The same review found that anti-cancer large-volume SC products typically require 5.0–20.0 mL doses every three weeks and are administered by healthcare professionals, while non-cancer large-volume SC products are typically self-administered monthly and most often fall below 5.0 mL.
Those differences reinforce the need for product-specific design. In oncology, larger SC volumes may be acceptable in a healthcare professional–administered setting if they reduce infusion burden or fit into an established care workflow. In chronic non-cancer indications, self-administration may place more emphasis on ease of use, patient confidence, storage, device handling, and administration time. A large-volume device might be well suited to one scenario and poorly suited to another, even when the underlying formulation challenges are similar.
The development question is therefore not only “How much volume can be injected?” but “What volume, viscosity, device format, administration time, and training model make sense for this product and this patient population?” That question should be asked early, because late changes to concentration, volume, or device format can have consequences for formulation stability, manufacturing strategy, clinical evaluation, and patient acceptance.
Patient Comfort is a Development Variable
Patient comfort can sometimes be treated as a human-factors concern that becomes most relevant after the formulation and device are largely defined. For high-concentration biologics, that sequence is risky. Comfort is influenced by formulation properties, device design, injection process, and patient-related factors, which means it is shaped by decisions made throughout development.
Injection-site pain is a subjective side effect commonly reported with SC administration of biological agents.6 Multiple factors can contribute to that experience, including formulation attributes such as pH, volume, and excipients, features of the injection process, and patient-related factors such as low body weight, gender, and age. A broader review of SC injection pain similarly identifies needle features, injection site, injected volume, injection speed, osmolality, viscosity, formulation pH, and excipients, including buffers and preservatives, as factors that can influence pain sensation at the injection site.7
This evidence supports a development approach in which comfort is treated as an integrated product attribute. It is not enough to select a device and then ask whether patients can tolerate it. The formulation and device together create the administration experience. A change in excipient selection can affect stability and pain. A change in concentration can alter viscosity and volume. A change in device format can influence injection time, perceived control, and training needs. A change in injection site can alter the patient’s experience of the same product.
The subjective nature of injection-site pain also matters. A product may be well tolerated by many patients but still create meaningful barriers for some users. That is particularly important for therapies intended for repeated use. A single uncomfortable injection in a controlled setting is different from a chronic regimen that requires patients to administer or receive the product repeatedly. Over time, small burdens can become adherence risks, especially if the patient already faces anxiety, dexterity challenges, treatment fatigue, or other barriers to confident use.
There are practical ways to reduce injection-related discomfort, but they depend on the product and setting. Interventions described in the literature include allowing biologics to reach room temperature before injection, choosing the most suitable injection device, selecting an alternative formulation when available, and providing effective training.6 These interventions show that patient comfort is not controlled by formulation alone. It depends on preparation, presentation, device choice, instruction, and user confidence.
For developers, the main lesson is that comfort should be included in the definition of product performance. A formulation that meets concentration, stability, and quality targets may still be incomplete if it creates unnecessary administration burden. A device that delivers the full dose may still be poorly matched to the patient population if it requires too much force, takes too long, or makes users anxious. Comfort is not separate from technical success. It is one way technical success becomes meaningful in practice.
Large-Volume Subcutaneous Delivery Is Expanding the Administration Landscape
Large-volume SC delivery is not a niche formulation question. It reflects a broader shift in how biologics are being designed, administered, and experienced. The systematic review of large-volume SC biopharmaceuticals identified 182 products, predominantly monoclonal or bispecific antibodies, representing approximately 15% of all IV and SC biopharmaceuticals reviewed.5 That landscape shows that higher-volume SC delivery is becoming a meaningful part of biologic product development.
The administration patterns within that landscape are not uniform. Anti-cancer large-volume SC products typically involve 5.0–20.0 mL doses administered every three weeks by healthcare professionals.5 Non-cancer large-volume SC products are typically self-administered monthly and most often fall below 5.0 mL. These differences suggest that the future of SC biologic delivery will not be defined by a single device type or volume threshold but by indication, setting, dose, patient population, and the level of support available during administration.
That distinction is important for development strategy. A healthcare professional–administered oncology product may be designed around clinic workflow, staff time, chair time, dose preparation, and tolerability in a supervised environment. A self-administered chronic therapy may be designed around storage, portability, ease of instruction, patient confidence, reduced handling complexity, and a reasonable administration experience at home. Both products may be high-dose biologics. Both may require formulation and device innovation. But the practical success criteria differ.
Large-volume SC products also change how developers think about administration time. For a small-volume injection, speed may be a convenience factor. For a larger-volume product, delivery time may become a defining feature of the product experience. A device that enables larger-volume administration may reduce the need for IV infusion, but it may also require the patient to remain connected to a delivery system for a period of time. Whether that tradeoff is acceptable depends on the disease area, dosing frequency, care setting, patient expectations, and available alternatives.
The review also concludes that large-volume drug delivery systems and novel formulations are important for reducing injection volumes.5 This point reinforces the connection between formulation and device strategy. Formulation innovation may reduce volume by enabling higher concentrations. Device innovation may make larger volumes or more viscous formulations feasible. Delivery-enhancing approaches may expand what can be administered into the SC space. The most effective strategy may involve more than one of these levers.
As this landscape grows, development teams will need to avoid applying small-volume assumptions to large-volume products. A product that exceeds traditional SC volume limits may still be appropriate for SC administration if the formulation, device, administration setting, and patient experience align. Conversely, a product that fits within a nominal volume target may still fail to meet real-world expectations if it is difficult, painful, slow, or inconvenient to administer. Volume matters, but it is only one part of the administration profile.
Why Formulation and Device Strategy Need to Start Earlier
High-concentration biologics expose the limitations of a sequential development model. If molecule selection, formulation development, device selection, and patient experience evaluation occur in separate phases, programs may discover too late that a clinically attractive dose is difficult to deliver. Earlier integration does not eliminate tradeoffs, but it makes them visible when there is still time to act.
The starting point is developability. High-concentration formulation development can involve risks such as aggregation, precipitation, opalescence, particle formation, and high viscosity.2 Early experimental, low-mass, high-throughput, and in silico methods can help predict those liabilities before formulation options narrow. For high-dose biologics, these tools can help teams understand whether a molecule is likely to support the concentration, stability, and viscosity profile required for the intended route of administration.
The next layer is formulation optimization. Excipients, such as salts and amino acids, may reduce viscosity at a given antibody concentration, but excipients that lower viscosity can also affect protein stability.3 This creates a familiar development tension: the formulation must support both administration and product quality. The device cannot compensate for every formulation limitation, and the formulation cannot be optimized without considering how the product will be delivered.
The third layer is device feasibility. A product intended for SC administration must be evaluated in relation to injection force, dose volume, flow rate, administration time, and user interaction. Those factors can shape whether a product is better suited to a prefilled syringe, an autoinjector, a larger-volume delivery system, a healthcare professional–administered device, or another configuration. Because the delivery system can affect the product experience, device considerations should inform the target product profile early rather than being added after formulation decisions are locked.
The fourth layer is patient use. Injection-site pain and discomfort can be influenced by formulation factors, injection process factors, and patient-related factors.6 Pain sensation after SC injection can also be influenced by needle features, injection site, volume injected, injection speed, osmolality, viscosity, formulation pH, and excipients.7 These variables span multiple functions, which means no single team owns the entire comfort profile. Formulation scientists, device engineers, clinicians, human-factors specialists, and manufacturing teams all contribute to the eventual patient experience.
This is where CDMOs and development partners can play a valuable role, provided they are engaged early enough. High-concentration biologics require coordination across formulation screening, analytical characterization, manufacturability assessment, fill–finish considerations, device compatibility, and administration strategy. A partner that sees only one slice of the problem may optimize locally while creating issues elsewhere. A partner that can connect concentration, viscosity, stability, device feasibility, and patient experience can help reduce the risk of late-stage redesign.
That integrated perspective is especially important as more biologics are designed for SC delivery from the outset. If SC delivery is a core part of the product’s value proposition, it should be reflected in early development choices. The target concentration should be considered alongside likely dose, viscosity, device format, and administration setting. The formulation screen should account for stability and injectability. Device options should be evaluated before the program becomes locked into a volume or viscosity range that narrows the design space. Patient comfort should be treated as a performance requirement, not an afterthought.
Designing for the Product, the Device, and the Patient
High-concentration biologics require developers to think beyond the molecule and beyond the container. The product is ultimately experienced as an administration event. That event may be brief or extended, self-administered or healthcare professional–administered, small-volume or large-volume, manual or device-assisted. Its success depends on whether the formulation, device, and patient-facing workflow can function together.
The core development challenge is balancing competing constraints without reducing the problem to any single one of them. Concentration can help reduce volume, but it may increase viscosity. Viscosity reduction can support administration, but the excipient strategy must protect stability. Larger-volume delivery can make high-dose SC administration possible, but it may change device requirements, administration time, and patient expectations. Device innovation can expand what is feasible, but it must still fit the product and user. Patient comfort can be improved through formulation, device, and training choices, but those choices need to be built into development rather than added at the end.
For some programs, the right solution may be a very high-concentration formulation that can be administered in a small volume. For others, the right answer may be a larger-volume device that reduces the need to push concentration to the edge of formulation feasibility. For still others, a combination of formulation optimization, delivery-device innovation, and administration-setting strategy may be required.
This is also why the high-concentration biologics conversation should not be framed only around technical difficulty. The challenge is real, but so is the opportunity. SC administration can support new models of care when the product is designed appropriately. High-concentration and large-volume strategies may help move biologics into more convenient administration formats, reduce reliance on IV infusion in some contexts, and better align therapy with patient and healthcare-system needs. Those benefits depend on rigorous development work that connects formulation science with device engineering and patient use.
The strongest programs will define success in practical terms. Can the product be formulated at the required concentration without unacceptable instability or viscosity? Can it be manufactured and filled reliably? Can it be delivered through the selected device with acceptable force, flow, and administration time? Can patients or healthcare professionals use the product confidently? Can the formulation and device support the intended dosing frequency, setting, and patient population? These questions should be addressed together, because the answer to one can change the answer to another.
High-concentration biologics make that interdependence impossible to ignore. Viscosity, injection force, comfort, and administration time are not separate development boxes to check. They are connected expressions of the same underlying product design. The earlier developers recognize that connection, the better positioned they are to build biologics that are not only potent and stable but also deliverable, usable, and aligned with how patients actually receive care.
