Capsule and Granulation Sourcing: 7 Smart Checks Before Scale-Up

Capsule and Granulation Sourcing Starts with the Dosage Form

Before selecting a capsule supplier or granulation process, the intended dosage form should be clearly defined.

For a capsule project, this may include:

• Hard capsule or another capsule format
• Gelatin or vegetarian capsule shell
• Target capsule size
• Target fill weight
• Powder or granulated fill
• Color and appearance requirements
• Printing or branding requirements
• Market-specific requirements

Hard gelatin capsule shells, for example, consist primarily of gelatin and water and may contain additional components such as colorants, opacifiers and other processing aids. 

For nutraceutical and functional-ingredient products, vegetarian or plant-based capsule options may also be considered depending on the product positioning and target market.

The important point is that capsule selection should not happen independently from the formulation.

A capsule has a defined physical volume, while the formulation has a defined mass, bulk density and flow behavior. These variables have to work together.

1. Match Capsule Size with the Actual Fill Requirement

One of the most common procurement mistakes is choosing a capsule size based only on the amount of active ingredient.

The actual filling requirement depends on the total formulation weight and the physical characteristics of the blend.

Two formulations containing the same amount of active ingredient can require different capsule sizes because their excipient composition, bulk density, particle size and packing behavior are different.

For this reason, the development team should establish at least:

• Total fill weight per capsule
• Approximate bulk density
• Target capsule size
• Expected fill-weight variation
• Powder or granule characteristics
• Filling equipment or filling method

A theoretical calculation may help with initial screening, but actual filling trials are much more informative.

A formulation that fits within a particular capsule volume on paper may behave differently when it reaches the filling machine.

2. Evaluate Powder Flow Before Blaming the Capsule

When capsule filling becomes inconsistent, the capsule shell is not necessarily the problem.

Powder behavior can be the limiting factor.

Poor flowability may contribute to inconsistent feeding, bridging, segregation, variable fill weights and difficulties during automated filling. Published research has found a significant relationship between powder flow properties and capsule fill weight and weight variability. 

Relevant powder characteristics may include:

• Particle size distribution
• Bulk density
• Tapped density
• Compressibility
• Cohesion
• Particle morphology
• Moisture content
• Electrostatic behavior
• Flowability

This is particularly important when a formulation contains several low-dose active ingredients or fine powders.

A formulation can meet its chemical specifications and still perform poorly during manufacturing because its physical properties are unsuitable for the selected process.

That is why a COA alone may not tell the whole manufacturing story.

3. Decide Whether Granulation Is Actually Necessary

Granulation should not automatically be viewed as an additional processing step.

It should be considered when the powder properties create a practical manufacturing problem that cannot be adequately addressed through formulation adjustment or process optimization.

Granulation can modify particle size, density and flow characteristics. Pharmaceutical literature describes granulation as a process used to improve properties such as flowability, compressibility and the handling of powder blends. 

Depending on the formulation, options may include wet granulation, dry granulation or other particle-engineering approaches.

The choice should depend on the material and the intended process.

For example, a moisture-sensitive formulation may require a different approach from a formulation that can tolerate an aqueous granulation step. Similarly, a formulation containing heat-sensitive components may require careful consideration of processing conditions.

The procurement question therefore should not simply be:

“Can this supplier provide granulation?”

A better question is:

“Which granulation process is suitable for this formulation, and what specifications can the supplier consistently achieve?”

4. Define Granule Specifications Before Ordering

Once granulation becomes part of the project, the granulated material should be treated as a defined intermediate rather than simply “processed powder.”

The specification may need to address:

• Particle size distribution
• Moisture content
• Bulk density
• Flowability
• Granule strength
• Fines content
• Appearance
• Active content
• Content uniformity, where applicable
• Storage conditions
• Packaging

Particle size is particularly relevant because excessive fines may negatively affect flow, while excessively large or dense granules may behave differently during filling or downstream processing.

Granulation research also shows that changes in excipient composition and processing conditions can affect granule size, density, compressibility and flow behavior.

This means that a granulation supplier should not be evaluated only by whether it can produce granules. The more important question is whether it can repeatedly produce granules within the required physical and chemical specification.