Pellet Technologies

What does is mean speakting about pellet technologies? First of all: pellets are starter beads. They consist of microcrystalline cellulose, tartaric acid, sugar or other materials. The beads have not only a diameter between 100 and 1,400 µm but also show a comparably small size distribution. Subsequently, this allows defined drug layering of API (active pharmaceutical ingredient). Similarly, drug layering of excipients targets modified release times of your product. Above all, perfect results can be obtained thanks to perfect pellet properties, such as low friability, high degree of sphericity and smooth surfaces.

What is the principle of pellet technologies?

In this paragraph, we shed some light on the principle of pellet technologies. In short, the API is fixed to the outside of a pellet by using a binder or by spray technology. To clarify, API contents of 0.1 % up to 80 % are possible. The pellet is also often coated with excipients (single or multiple coating), which take over technical functions. These functions are for example mechanical protection, or adjustment of the drug delivery system. Along with the selection of excipients, different drug release profiles can be achieved, such as delayed, targeted or pulsed release. Different process technologies can be employed for layering and coating.

In other words: With pellet technologies you are able to create your best choice of oral dosage form for your application.

Pellets: Oral solid dosage forms

Pellets or micropellets are comparably small. In particular, the size range is about 100 µm to 1,400 µm. This allows surely certain characteristics and offers advantages for oral solid dosage forms.

Multiparticulate drug delivery system with pellets:

API is distributed on multiple small discrete units
particle size is approximately between 100 µm and 2000 µm
reduced food effect and variability in systemic absorption
reduced risk of dose dumping
good compliance (taste masking / palatability / easy to swallow)

Advanced drug release technologies:

tailored drug release profiles
good site specific drug delivery (e.g. colon targeting)
improved therapeutic effectiveness and safety
improved compliance (less frequent dosing)

Technologies for tailored drug release profiles

Individual coating layers allow diverse drug release profiles. In particular, these profiles are specifically tailored to the application. Especially immediate or controlled release profile are possible. Furthermore, it is also technically possible to define a lag time and thus initiate a pulsatile or biphasic release. As an illustration: pH dependent releases are adjustable for targeting the API towards defined location of dissolution.

release depends on pH value (e.g. enteric coating)

pulsatile release / lag time
biphasic release
targeting (e.g. colon)

Immediate release
Controlled / modified release

Optimised dosing interval and safety

In the following, the sketches below clearly show the advantages of optimizing the release time. Namely, a modified release time increases firstly the customer’s compliance by longer dosing intervals, secondly increases the dosing safety and finally realizes a desired uptake effect.

immediate release

modified release

Pellets: Most convenient oral solid dosage form for every age

To clarify, multiparticulates – such as micro pellets, granules or mini tablets – serve the best oral dosage form for small children and elderly adults.

paediatric medicines for

premature
newborn
baby
child

adult medicines for

adolescents
adults

geriatric medicines for

seniors (65+ years)
end of life

Basic pellet technologies & composition

A pellet can obviously be a starter bead with or without the presence of an API. Consequently, the API is part of the inner starter pellet or of one of the functional coatings.

Pellet technologies realize drug layered starter pellets. For example, these technologies are:

Wurster (bottom spray)
Rotor dry powder layering

Wurster (bottom spray) for pellet coating

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The Wurster process is a Glatt-specific process developed by Dale E. Wurster in the 1950s.
It describes a coating process used in fluidized bed coating. The bottom spray process can be used as a variation of Wurster’s process.
Likewise, the spray liquid is sprayed from the bottom to the top. The spray nozzles are integrated in the bottom plate and are thus completely surrounded by the particles to be coated.

process mode

batch mode

starting material

starter pellets ≥ approx. 100 µm

processing of the API

from a liquid (chemical stability in liquid!)

API content

less than 0.1% – 80%

smallest pellet size achievable

~ 200 µm for low/medium dosed API

preferred for

chemically stable API

Rotor dry powder layering for pellet layering

Dry powder layering is a process for constructing active substance pellets. For instance, a starter core is coated with an ingredient in powder form. Nonetheless, a binding solution helps fixing the ingredient to the starter core. There is certainly a main advantage of this process compared to layering with liquid active substances: The processing time is significantly reduced which leads to a higher efficiency. With optimal process settings, hourly weight gains of up to 300 percent are possible.

On the other hand, rotor dry powder layering is the method of choice, if the API cannot be mixed up in liquids, but needs dry processing.

The result are dust-free, very round active substance pellets with a narrow particle size distribution. Therefore, rotor dry powder layering is an efficient solution for refining and functionalizing solids.