Why Scale-Up Surprises Happen
The development laboratory is a controlled, forgiving environment. The scientist is present at every step, making small adjustments and observations that never make it into the batch record. The equipment is flexible. The batch size is small enough that a failed experiment costs almost nothing.
GMP manufacturing is the opposite. The process must be executed by operators following a fixed procedure, using equipment that may differ substantially from the development kit, in a regulated environment where every deviation generates a quality event. The tacit knowledge the development scientist held in their head is not available at the manufacturing scale.
Scale-up failures are not usually caused by poor science. They are caused by the gap between what was understood about the process and what was written down.
The Most Common Scale-Up Failure Modes
| Failure Mode | What Causes It | How to Prevent It |
| Blend uniformity loss | Mixing dynamics differ between lab and GMP blenders; segregation occurs at larger scale | Characterise blend uniformity at intermediate scale; define blend time and speed as critical process parameters |
| Granule size distribution shift | High-shear granulators at GMP scale apply different shear profiles; impeller geometry differs | Run granulation at intermediate scale; define wet mass endpoint by torque or power consumption rather than time |
| Tablet hardness and friability out of range | Compression force requirements differ at GMP scale; punch tooling geometry may differ | Run a compaction simulation on the GMP press before the GMP batch; define compaction force range with in-process controls |
| Dissolution failure | Particle size distribution of API or granules shifts at scale; compression force affects tablet porosity and dissolution | Confirm dissolution at each scale; link dissolution to particle size and compaction parameters |
| Coating defects | Pan geometry and air volume differ at scale; spray rate and atomisation pressure need re-optimisation | Develop coating parameters using scale-up relationships; run scale-up trial before GMP batch if possible |
| Yield loss | Process losses at each step accumulate; GMP equipment dead volumes are larger | Map equipment dead volumes; adjust batch size to account for losses; define acceptable yield range |
Scale-Up Is a Scientific Activity, Not Just an Operational One
The most common mistake in scale-up is treating it as a task for the manufacturing team rather than for the formulation scientists. The manufacturing team knows how to run the equipment. The formulation scientists know why each parameter matters and what the process is sensitive to. Both are needed.
The practical outcome of good scale-up science is a set of documented critical process parameters (CPPs) with defined acceptable ranges, and a clear link between those parameters and the critical quality attributes of the product. That link, the process understanding that connects what you do to what you get, is what process validation is built on.
The Role of Design of Experiments in Scale-Up
Design of experiments (DoE) is the systematic approach to understanding how process parameters interact to affect product quality. Rather than changing one variable at a time, DoE changes multiple variables in a structured pattern that allows their individual effects and interactions to be quantified efficiently.
For scale-up, DoE at the development or intermediate scale builds the process understanding that makes GMP-scale manufacturing predictable. A team that has run a DoE mapping the effects of granulation endpoint, drying temperature, and blending time on granule properties arrives at the GMP scale with a model of the process, not just a set of fixed instructions.
Process Validation: What Regulators Expect
The FDA’s process validation guidance describes a lifecycle approach with three stages: process design (where development knowledge is captured), process qualification (where the commercial-scale process is confirmed to perform consistently), and continued process verification (where ongoing monitoring confirms that the validated state is maintained). For clinical supply, the same thinking applies, though the formal process validation is typically deferred to the commercial stage.
At the GMP clinical batch stage, the expectation is that the process is sufficiently understood that the batch is manufactured according to a defined process with identified critical steps and controls, and that any deviations are investigated meaningfully. The process understanding accumulated during scale-up is what makes that possible.
How Ardena Manages Scale-Up at Ghent
Ardena’s oral solid development and manufacturing team at Ghent conducts development, intermediate-scale, and GMP manufacturing at the same site. Formulation scientists remain involved in the GMP manufacturing phase, providing the scientific context that operators need when unexpected results arise. The team documents process understanding progressively through development, building the CPP and CQA linkages that support both the manufacturing process and the CMC regulatory filing.
