Key Considerations in Capsule Filling

A variety of industries rely on efficient capsule-filling capabilities to cost-effectively produce products such as vitamins, supplements, and medication. Though it may seem relatively simple in theory, capsule filling is quite delicate, and measurements must be exact to ensure products are safely within prescribed dosage levels. This process must also be easily repeated to ensure that each capsule is filled consistently to standard.
There are numerous factors that must be accounted for in a capsule filling operation. This essay will discuss key considerations involved with filling capsules for pharmaceuticals, nutraceuticals, and other applications.

Formulation

Most formulations may be encapsulated in some form using hard capsules, granules, blends, or coated pellets. Other common oral dosage methods include tablets and micro-tablets, as well as smaller-sized capsules. Many products are available in several of these forms to give a choice to the medical provider or consumer.
There are a few caveats regarding capsule filling, however. For example:
  • Any mixture that contains reactive aldehydes isn’t suitable for use in capsule filling. Reactive aldehydes have a reaction with the gelatin capsule material known as cross-linking which may cause the encapsulated material to release more slowly than intended.
  • In capsule filling, solids with insufficient flow properties will be difficult to control during the filling process. This may result in underfilled or overfilled capsules of the wrong weight, which must then be discarded.
    Low-viscosity liquids tend to leak from a two-part capsule immediately after filling, which can impact the dosage of the capsule.
  • Hygroscopic liquids absorb additional moisture. As such, they will absorb moisture from the capsule material, leaving it brittle and fragile.

Size & Fill Weight

Determining the appropriate capsule size and fill weight ultimately requires an understanding of the expected dosage to be contained within the capsule. This can vary based on the formulation, as products vary widely in density. To determine the appropriate capsule size and fill weight, define the tapped density of granulates and powders. This will facilitate an understanding of the volume that the capsule must contain to reach the proper dosage and the selection of an appropriate capsule size.
Capsule manufacturers typically offer capsules in a broad range of sizes to accommodate the widest range of products.

Clinical vs. Commercial Production

  • Medicinal capsules used in clinical trials often have customized dimensions or geometries, which may require special machines or tooling to produce.
  • Clinical trial batch sizes are relatively small, which allows capsules to be manually filled.
  • Conversely, a drug or product that has gone to market must be produced in volumes vastly exceeding what can be accomplished by hand. This requires automated filling.
  • Automated filling for high-volume production means formulating a powder, granular mixture, or liquid that is suitable for use with automated capsule filling machines.

Automated vs. Manual Capsule Filling

Automated and manual capsule filling each offer their own set of advantages. Manual capsule filling offers benefits such as:
  • Minimal equipment investments
  • Easier mid- and post-process cleaning
  • Mitigates time spent on equipment adjustments
  • No dead space volume in capsules, which is essential for clinical trials
Automated capsule filling offers its own benefits, including:
  • Much faster than manual filling
  • Reliable and repeatable, providing closer-tolerance fills between capsules
  • Easy dose adjustments
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