Challenges and opportunities in the encapsulation of liquid and semi-solid formulations into capsules for oral administration

The encapsulation of liquids and semi-solids provides solutions for convenient delivery through improved oral absorption of poorly water-soluble drugs. In addition, low dose (content uniformity), highly potent (containment), low melting point drugs, those with a critical stability profile and those for which a delayed release is required are candidates for liquid or semi-solid formulations. Both hard and soft capsules can be considered and in each case the capsule wall may comprise gelatin or some other suitable polymer such as hypromellose. The choice of a hard or soft capsule will depend primarily on the components of the formulation which provides the best absorption characteristics as well as on the physical characteristics, such as the viscosity of the formulation and the temperature at which the product needs to be filled. Numerous excipients are available for formulation of lipid-based systems and their compatibilities with hard gelatin capsules have been tested. The availability of new enhanced manufacturing equipment has brought new opportunities for liquid-filled hard capsules. Filling and sealing technologies for hard capsules, provides the formulator with the flexibility of developing formulations in-house from small scale, as required for Phase I studies, up to production.