Bead compacts. I. Effect of compression on maintenance of polymer coat integrity in multilayered bead formulations

Little information is available on the compactability of beads for oral sustained-release dosage forms. It is known that polymer-coated beads may fuse together to produce a non-disintegrating controlled-release matrix tablet when compressed. This study evaluates the effect of compression on beads with multiple layers of polymer and drug coat, and the effect of cushioning excipients and compaction pressure on drug release from compressed bead formulations. The multilayered beads consist of several alternating layers of acetaminophen (APAP) and polymer coats (Aquacoat) with an outer layer of mannitol as a cushioning excipient. Percent drug release versus time profiles showed that the release of drug decreases from noncompacted beads as the amount and number of coatings increases, with only 43% of drug released in 24 hr for coated beads with 10 layers. It was shown that the compacted multilayered beads will disintegrate in gastrointestinal fluids, providing a useful drug release pattern. It was shown that beads of drug prepared by any method can be spray-layered with excipients such as Avicel and mannitol. Spray-layering of the cushioning excipient onto beads can provide an effective way to circumvent segregation issues associated with mixing of the polymer-coated beads and powdered or spherical/nonspherical cushioning excipients. Spray layering of the cushioning excipient can also provide excellent flow properties of the final formulation as visually observed in our experiments. Triple-layered caplets (TLC) were also prepared with outer layers of Avicel PH-101 or polyethylene oxide (PEO), and a center layer of polymer-coated beads. For TLC, the polymer coating on the beads fractured, and nondisintegrating matrix formulations were obtained with both caplet formulations.