Drug-Layering Core Pellets with Wurster Fluidized Bed Technology

Drug-Layering Core Pellets Overview

Drug-layering core pellets use Wurster fluidized bed technology, also called bottom-spray coating, which remains the most preferred method in pharmaceutical manufacturing. Usually, sugar or microcrystalline cellulose (MCC) starter pellets serve as the base. In this batch process, a liquid containing the active pharmaceutical ingredient (API) coats pellets which as in size 100 μm or larger. However, the API must remain chemically stable in the layering solution.

Advantages of Wurster Technology for Drug-Layering Core Pellets

Efficient for Low- to Medium-Dose APIs

Wurster technology works very well for low drug loads. Therefore, it ensures excellent content uniformity. For low- to medium-dose APIs, the minimum core particle size should be about 200 μm.

Flexible Drug Load Capacity

The API content in drug-layered core pellets ranges from less than 0.1% to 80%. Typically, a single layering step achieves up to 60% drug load. When splitting the batch into multiple steps higher values are accessible.

Consistent Quality and Uniformity

Both bulk uniformity and content uniformity are critical for low-dose drugs. Moreover, Wurster technology ensures even drug distribution, producing highly homogeneous pellets.

Drug Layering Applications

Levocetirizine drug layering liquid
A Levocetirizine solution with a binder coated 70 kg of 200–400 μm starter beads in an 18” high-speed Wurster system. Consequently, yields for three scale-up batches ranged from 98.6% to 100%. Bulk uniformity testing of Levocetirizine immediate release pellets (assay of Levocetirizine: 0.3% w/w) showed a relative standard deviation (RSD) of 0.8–1.3% [1].
Hydrocortisone core pellets
In commercial production, 160 kg of Hydrocortisone core pellets used a 32” Wurster unit. An aqueous Hydrocortisone suspension coated CELLETS® 350 over three hours. As a result, 0.5 mg capsules containing taste-masked, drug-layered pellets (assay of Hydrocortisone: 0.81% w/w) achieved a content uniformity RSD of 0.9% [1].
Commercial production of a blockbuster product
A blockbuster product produced 600 kg of drug-layered pellets with 40% w/w drug load in a 46” Wurster unit. Starting with 275 kg of starter pellets, 1,300 kg of organic solvent-based suspension was sprayed over 3.1 hours using six high-speed nozzles at a spray rate of 7 kg/min. Thus, the process achieved yields over 98% with less than 0.2% agglomeration [1].
Metoprolol Succinate drug-layered pellets
In a 32” Wurster unit, 400 kg of Metoprolol Succinate pellets were produced. A total of 1036 kg of a 31% w/w aqueous Metoprolol solution, combined with silicon dioxide as an anti-tacking agent, coated 77.7 kg of sugar pellets sized 212–300 μm. After 8.3 hours of spraying, drying, and cooling, the batch reached 77.7% w/w drug load. The final yield was 98.4%, with a particle size of 425–710 μm [1].

drug-layering process of pharmaceutical pellets

Summary

Drug-layering core pellets using Wurster technology offer precise, scalable, and uniform drug coating. Furthermore, this method works for low- and high-dose APIs. Therefore, manufacturers achieve consistent quality, high yield, and excellent content uniformity, making Wurster fluidized bed technology the preferred choice for drug-layered pellets.

References

[1] Multiparticulates, Modern Oral Drug Products for our Society – Part 1,1; seminar series by Dr. Norbert Pöllinger.

Expert’s opinion

The Wurster (bottom spray) fluidized bed technology is the most commonly used and preferred method for drug-layering core pellets. Most likely starter beads are sugar or MCC starter pellets. In this batch process, a liquid containing the active pharmaceutical ingredient (API) is applied to starter pellets that are 100 μm or larger.