Factors Influencing Design and Development 1361 API Characteristics

High dose drugs must of necessity comprise a major component in a microparticle. Such high inclusion level may require that a strong binder be used to ensure adequate particle robustness for processing. It may be possible, on occasion to apply the functional coat directly to the drug, no pregranulation being needed.

Functional coat

Functional coat

Fig. 13.5 Particle design depending on dose strength, left: high dose, right: low dose

Drug layer

Fig. 13.5 Particle design depending on dose strength, left: high dose, right: low dose

Low dose drugs can be layered onto an inert core. The active can either be layered as solid, being fixed by a concentrated polymer binder solution (powder layering) or alternatively be applied as solution or suspension. Solution application can provide uniform dense API layers. It may also be possible to embed drug in the functional polymer.

Application from aqueous systems needs to take account of drug stability, viz., potential for hydrolytic degradation. However, propensity for hydrolysis may not mean that degradation is an issue, since contact time with water during coating is limited and only happens until the surface is sealed. Prudent process design and appropriate process controls may obviate hydrolysis enabling aqueous coating. Drug interactions with nonaqueous solvents or residues therein also need to be considered during process design.

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