Ian Smales
Drug Product Design
Pfizer, Sandwich, Kent

Although capsule formulations generally contain fewer excipients than tablet blends, successful capsule production also involves precise manipulation of the shells as they are aligned and filled.  The capsule shell needs to be considered as both primary packaging and an additional excipient, especially where the capsule shells are gelatine.

The majority of high speed capsule filling machines employ either the Dosator or the Dosing Disc filling mechanism. Both of these processes involve a degree of compaction and there have been a number of attempts to mimic and thereby understand this crucial stage of the filling process.   In recent years the instrumentation of the tablet compaction process has become widespread but the lower forces involved in capsule filling and the geometry of capsule filling machines have hindered the development of capsule filling simulators.

In the Dosator mechanism, the required dose is captured within a tube as it descends into the powder bed.   The dose is lightly compressed by a descending piston and then ejected into the waiting capsule body, prior to being capped and ejected.  The 3P Innovation Laboratory Dosator can be fitted with any size of dosator and reproduces the action of a Dosator type capsule filling machine.   Two miniature load cells and a laser displacement sensor are used to record the force, position & velocity of the dosator piston at key points throughout the powder plug formation & ejection process.   The data thus obtained can be used to screen and compare capsule blends, inform the choice of excipients and assess the effect of API on capsule filling performance.