Continuous direct compression can provide a simplified alternative pathway for selected spray-dried dispersion formulations when supported by a material-property-driven development strategy.

Amorphous solid dispersions (ASDs) have become a leading formulation approach for oral drug candidates whose absorption is limited by poor aqueous solubility. By dispersing the API in a polymeric matrix, spray drying can generate an amorphous form of the API that improves solubility and dissolution behavior. This has made spray-dried dispersions (SDDs) an important enabling technology for many small-molecule development programs.

While spray drying enables the generation of ASDs that enhance solubility and bioavailability, it can also produce powders that are challenging to convert into tablets. SDD powders often exhibit low bulk density, fine particle size, cohesive behavior, and electrostatic sensitivity. Some of these attributes may influence dissolution performance, but they are primarily relevant due to their impact on downstream manufacturability. These characteristics can challenge downstream feeding, blending, powder transfer, tablet weight control, and content uniformity. As a result, the downstream development path for SDD-based tablets has historically included an intermediate granulation step before final blending and compression.

That choice is understandable: a key driver for selecting granulation is to improve powder density, flow, and handling. Further, it provides a familiar and predictable route for processing challenging powders. Granulation can reduce the impact of variability in certain powder properties and powder-handling challenges; although, it introduces its own sources of variability that must also be controlled and understood. However, reliance on granulation as the default means of compensating for powder-property variability may become less important when spray drying is operated within a robust and well-controlled design space and the resulting particle properties are consistently achieved at the intended manufacturing scale. As continuous manufacturing platforms mature and material characterization becomes more predictive, it is worth asking whether granulation should remain the default pathway for all SDDs or whether selected systems can move directly from spray drying to tableting.

Why Granulation Became the Default Route

Granulation has historically played a practical role in tablet development. When powders flow poorly, segregate, or compress inconsistently, dry or wet granulation can convert them into a more processable intermediate. For SDDs, dry granulation is often attractive because it can improve density and handling while avoiding the intentional liquid exposure and drying steps associated with wet granulation. This can be important for amorphous or moisture-sensitive systems, 2,3 where exposure to water or other liquids may increase the risk of phase behavior changes or chemical instability.

In early development, the decision to granulate may also be influenced by pragmatic constraints. API availability can be limited, powder properties may not yet be fully optimized, and development teams often need a robust pathway that can support rapid progression. Specifically, this can routinely require spray drying at very small scales, where it becomes challenging to fully optimize spray-drying parameters and particle engineering strategies to achieve the powder properties that may be representative of future larger scale batches. Consequently, roller compaction may be selected as a purposeful risk-mitigation strategy to compensate for sub-optimal powder properties, even though subsequent optimization could potentially enable direct compression.

Although direct compression is typically the preferred tablet manufacturing route because it provides the simplest path from blend to final dosage form 7, its practical operating space in batch mode can be constrained by evolving API or intermediate properties during early phase development, as well as by flow, segregation, discharge, or transfer risks that emerge during scale-up or between batch variability. For SDD products, better control of the engineered intermediate can buffer API variability, but it may not always address the batch-specific handling and scale-up risks that often push development teams toward granulation.

The challenge is that early process choices can strongly shape the development path5, and become increasingly difficult to change within a highly regulated framework for pharmaceutical development and manufacturing. Once a granulation-based process is established, substantial process development work, analytical strategy, equipment selection, supply chain planning, and control strategy development accumulate around the granulation route. Even when product or process technology improvements later make a direct compression route technically possible, these opportunities may not be pursued because changing a mature processcan trigger regulatory refiling and disruption across multiple parts of the current manufacturing system for the intended product. A process pathway initially selected to manage uncertainty can easily become the default manufacturing strategy.

The Additional Cost and Complexity of Default Granulation

Granulation remains valuable when technically required but should be adopted based on demonstrated need rather than by default as it can add complexity across development, manufacturing, and lifecycle management. Additional unit operations introduce more process parameters, sampling points, equipment transfers, cleaning considerations, and quality controls. They can also create new sources of variability, including granule particle size distribution, density, lubrication sensitivity, compactability, fines management, and dissolution behavior.

For SDD-based products, this complexity is amplified because the SDD is already an engineered API-containing intermediate, designed to stabilize the amorphous form and enhance bioperformance. Granulating the SDD with excipients creates a second API-containing intermediate before final compression. When needed, this transformation is justified 6; when unnecessary, it adds another layer of material attributes, process variables, and quality considerations that must be developed, controlled, and understood.

Every additional powder transformation can also complicate root-cause analysis. If a tableting in-process control trends unexpectedly beyond its limits, an investigation must consider not only the SDD and final compression step, but also compaction, milling, intermediate blending, lubrication, hold conditions, and transfer between operations. In programs where speed, API conservation, and process understanding are critical, this added complexity can be significant.

The issue, therefore, is not whether granulation is useful. It is whether granulation is necessary for a given SDD product. If an SDD formulation can be fed, blended, lubricated, and compressed directly with adequate robustness, the development team may be able to remove a process step rather than optimize around it. This contrast between a default granulation-based pathway and a simplified CDC pathway is summarized in Figure 1.

Read the full article at PharmTech.com